7.1: Molecular Orbitals and Band Structure
- Explain the physical basis of the Hubbard and Mott models of metal-insulator transitions.
- Understand why good superconductors derive from bad metals.
- Know the structures and the periodic trends in band gaps and colors of semiconductors.
- Obtain the band gap of an intrinsic semiconductor from the temperature dependence of the conductivity.
- Predict the doping type when impurities or defects are introduced into a semiconductor.
- Correlate the band picture and Fermi level with n- or p-type doping.
- Understand the physical principles of operation of diodes, LEDs, solar cells, and FETs.
- Explain the differences in structures and electronic properties of crystalline and amorphous semiconductors.
The band model (like MO theory) is based on a one-electron model. This was an approximation we made at the very beginning of our discussion of MO theory: we used hydrogen-like (one-electron) solutions to the Schrödinger equation to give us the shapes of s, p, d, and f atomic orbitals. In a one-electron atom, these orbitals are degenerate within a given shell, and the energy differences between, e.g., 2s and 2p orbitals arise only when we consider the energy of an electron in the field of other electrons in the atom. Moving from atoms to molecules, we made linear combinations to generate one-electron molecular orbitals (and, in solids, one-electron energy bands). But as in multi-electron atoms, life is not so simple for real molecules and solids that contain many electrons. Electrons repel each other, and so their movement in molecules and in solids is correlated .
-
- 7.1.1: Prelude to Electronic Properties of Materials - Superconductors and Semiconductors
- Correlated electron effects give rise to metal-insulator transitions that are driven by small changes in temperature, pressure, or composition, as well as to superconductivity - the passage of current with zero resistance at low temperatures. In this chapter we will develop some simple models to understand these interesting and important electronic properties of solids.
-
- 7.1.2: Metal-Insulator Transitions
- Under experimentally accessible temperatures and pressures, Si and Ge are always semiconducting (i.e., insulating), and Pb is always metallic. Why is Sn different? The reason has to do with orbital overlap. Theory tells us in fact that any (and all) insulators should become metallic at high enough pressure, or more to the point, at high enough density. For most insulators, however, the pressures required are far beyond those that we can achieve in the laboratory.
-
- 7.1.6: Diodes, LEDs and Solar Cells
- Diodes are semiconductor devices that allow current to flow in only one direction. Diodes act as rectifiers in electronic circuits, and also as efficient light emitters (in LEDs) and solar cells (in photovoltaics). The basic structure of a diode is a junction between a p-type and an n-type semiconductor, called a p-n junction. Typically, diodes are made from a single semiconductor crystal into which p- and n-dopants are introduced.
-
- 7.1.7: Amorphous Semiconductors
- Amorphous semiconductors are disordered or glassy forms of crystalline semiconductor materials with network structures involving primarily covalent bonding. Crystalline silicon, which has the diamond structure, is an ordered arrangement of fused six-membered silicon rings and the local bonding environment of the silicon atoms is tetrahedral. The silicon atoms in amorphous silicon (a-Si) are also predominantly tetrahedrally coordinated, but there is no long-range order in the structure.


35.6: Chapter Summary
Urinary and bladder disorder drugs play a crucial role in the treatment of various conditions that affect the urinary system and bladder. These medications are designed to address specific symptoms or underlying conditions of these disorders, aiming to alleviate the individual’s discomfort and enhance the overall function of their urinary system.
In this chapter, a comprehensive analysis of commonly used urinary and bladder disorder drugs was presented. The chapter delved into the various classes of medications, such as urinary anti-infectives; antispasmodic, antimuscarinic, and anticholinergic drugs; urinary analgesics; urinary stimulants; and phosphodiesterase 5 inhibitors.
The chapter also highlighted the importance of a tailored treatment approach, considering individual client factors and the specific characteristics of each condition. Safety considerations, potential adverse effects, and efficacy profiles of these medications were also addressed, providing a comprehensive explanation of their therapeutic potential to improve urinary function and alleviate symptoms.
By understanding the different classes of drugs available and the particular aspects of urinary and bladder disorders, such as infections, muscle spasms, and abnormal contractions, nurses can tailor care plans to meet the specific needs of clients with urinary and bladder disorders.


8.1.E: The Chemical Foundation of Life (Exercises)
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- University of California, Davis
2.1: Atoms, Isotopes, Ions, and Molecules - The Building Blocks
Review Questions
If xenon has an atomic number of 54 and a mass number of 108, how many neutrons does it have?
- 54
- 27
- 100
- 108
- Answer
-
A
Atoms that vary in the number of neutrons found in their nuclei are called ________.
- ions
- neutrons
- neutral atoms
- isotopes
- Answer
-
D
Potassium has an atomic number of 19. What is its electron configuration?
- shells 1 and 2 are full, and shell 3 has nine electrons
- shells 1, 2 and 3 are full and shell 4 has three electrons
- shells 1, 2 and 3 are full and shell 4 has one electron
- shells 1, 2 and 3 are full and no other electrons are present
- Answer
-
C
Which type of bond represents a weak chemical bond?
- hydrogen bond
- atomic bond
- covalent bond
- nonpolar covalent bond
- Answer
-
A
Free Response
What makes ionic bonds different from covalent bonds?
- Answer
-
Ionic bonds are created between ions. The electrons are not shared between the atoms, but rather are associated more with one ion than the other. Ionic bonds are strong bonds, but are weaker than covalent bonds, meaning it takes less energy to break an ionic bond compared with a covalent one.
Why are hydrogen bonds and van der Waals interactions necessary for cells?
- Answer
-
Hydrogen bonds and van der Waals interactions form weak associations between different molecules or within different regions of the same molecule. They provide the structure and shape necessary for proteins and DNA within cells so that they function properly.
2.2: Water
Review Questions
Which of the following statements is not true?
- Water is polar.
- Water stabilizes temperature.
- Water is essential for life.
- Water is the most abundant molecule in the Earth’s atmosphere.
- Answer
-
D
When acids are added to a solution, the pH should ________.
- decrease
- increase
- stay the same
- cannot tell without testing
- Answer
-
A
A molecule that binds up excess hydrogen ions in a solution is called a(n) ________.
- acid
- isotope
- base
- donator
- Answer
-
C
Which of the following statements is true?
- Acids and bases cannot mix together.
- Acids and bases will neutralize each other.
- Acids, but not bases, can change the pH of a solution.
- Acids donate hydroxide ions (OH – ); bases donate hydrogen ions (H + ).
- Answer
-
B
Free Response
Discuss how buffers help prevent drastic swings in pH.
- Answer
-
Buffers absorb the free hydrogen ions and hydroxide ions that result from chemical reactions. Because they can bond these ions, they prevent increases or decreases in pH. An example of a buffer system is the bicarbonate system in the human body. This system is able to absorb hydrogen and hydroxide ions to prevent changes in pH and keep cells functioning properly.
Why can some insects walk on water?
- Answer
-
Some insects can walk on water, although they are heavier (denser) than water, because of the surface tension of water. Surface tension results from cohesion, or the attraction between water molecules at the surface of the body of water (the liquid-air/gas interface).
2.3: Carbon
Review Questions
Each carbon molecule can bond with as many as________ other atom(s) or molecule(s).
- one
- two
- six
- four
- Answer
-
D
Which of the following is not a functional group that can bond with carbon?
- sodium
- hydroxyl
- phosphate
- carbonyl
- Answer
-
A
Free Response
What property of carbon makes it essential for organic life?
- Answer
-
Carbon is unique and found in all living things because it can form up to four covalent bonds between atoms or molecules. These can be nonpolar or polar covalent bonds, and they allow for the formation of long chains of carbon molecules that combine to form proteins and DNA.
Compare and contrast saturated and unsaturated triglycerides.
- Answer
-
Saturated triglycerides contain no double bonds between carbon atoms; they are usually solid at room temperature. Unsaturated triglycerides contain at least one double bond between carbon atoms and are usually liquid at room temperature.


2.2: Matching Principle
The matching principle relates to income statement accounts. It states that expenses incurred during a period should relate to (or match up with) the revenues earned during the same period. This lets you know how much it cost you to produce the revenue you generated in a given period of time, such as a month.
You have probably heard that “It takes money to make money.” A business person contributes financial resources and hopefully uses them effectively to generate even more value. The matching principle looks at a window of time in terms of how much income came in and how much it cost to generate that income. The key here is the “window of time,” such as a month. It compares how much came in in sales in a month vs. how much was spent. Any revenue or expenses before that month or after that month are not considered.
Below is Timeline #1, which includes three months. The red bars represent revenue—three different jobs for $100 each. Job 1 was started in May and completed in June. Job 2 was started in June and completed in June. Job 3 was started in June and was completed in July. There was a total of $300 in revenue from these three jobs, but not all of it is earned in June. As you can see, only half of the revenue from Jobs 1 and 3 was earned in June.
The blue bars represent expenses. Expense 4 began in May and was incurred partially in May and partially in June. Expense 5 began in June and all of this expense was incurred in June. Expense 6 also began in June; some of it was incurred in June and some in July. There was a total of $180 of expenses, but not all of it was incurred in June. As you can see, only half of the expenses from Jobs 1 and 3 was incurred in June.
Let’s say we want to produce an income statement for June, our window of time. We want to include all the revenue and expenses that occurred in June, but none that occurred in May or July. We have to “chop off” the pieces of these transactions that did not occur in June to be left with only the parts that belong in June.
The result appears in the Timeline #2 below. In June, $200 of revenue ($50 + $100 + $50) was earned and is matched with $120 ($30 + $60 +$30) of expenses that were incurred in the same month. The net income for June, therefore, was $80 ($200 - $120).
Adjusting entries, discussed next, help do the job of matching the June revenue with the June expenses by “chopping” off amounts of transactions that do not belong in a given month.
2.2.1 Adjusting Entries
Adjusting entries are special entries made just before financial statements are prepared—at the end of the month and/or year. They bring the balances of certain accounts up to date if they are not already current to properly match revenues and expenses. So far we have dealt with companies that did not need adjusting entries under the cash basis of accounting. Now we will see situations where they are necessary and will be using the accrual basis of accounting.
Many ledger account balances are already correct at the end of the accounting period; however, some account balances may have changed during the period and but have not yet been updated. This is what you will do by making adjustingentries, and this will ensure that your financial statement numbers are current and correct. Adjusting entries are typically necessary for transactions that extend over more than one accounting period—you want to include the part of the transaction that belongs in the one accounting period you are preparing financial statements for and exclude that part that belongs in a previous or future accounting period. This relates to the matching process.
IMPORTANT: Each adjusting entry will always affect at least one income statement account (revenue or expense) and one balance sheet account (asset or liability).
2.2.2 Complete Accounting Cycle
Accounting is a cyclical process. It involves a series of steps that take place in a particular order during a period of time. Once this period of time is over, these same steps are repeated in the next period of time of equal length.
The complete accounting cycle involves these nine steps, done in this order:
| ACTION | WHEN | YOUR JOB | |
| 1. | Journalize transactions | Daily | THINK |
| 2. | Post to ledgers | Daily | COPY from journal; CALCULATE |
| 3. | Journalize the adjusting entries | End of month | THINK |
| 4. | Post the adjusting entries | End of month | COPY from journal; CALCULATE |
| 5. | Income statement | End of month | COPY from ledgers; CALCULATE |
| 6. | Retained earnings statement | End of month | COPY net income from income statement |
| 7. | Balance sheet | End of month | COPY from ledgers; ADD |
| 8. | Journalize the closing entries | End of month | THINK (same three entries) |
| 9. | Post the closing entries | End of month | COPY from journal; CALCULATE |
You have already learned how to complete seven of the steps. The remaining two steps, #3 and #4, are new and involve adjusting entries that update account balances that are not current just before preparing the financial statements.
IMPORTANT : Notice that adjusting entries are recorded BEFORE the financial statements are prepared and closing entries are recorded AFTER financial statements are prepared.
2.2.3 Adjusting Entry Accounts
The following list includes accounts whose balances may need to be brought up to date in the 10 adjusting entry transactions we will cover.
| ACCOUNT TYPE | ACCOUNTS | TO INCREASE | TO DECREASE | NORMAL BALANCE | FINANCIAL STATEMENT | CLOSE OUT? |
| Asset |
Accounts Receivable
Supplies Prepaid Rent Prepaid Insurance Prepaid Taxes Prepaid ANYTHING |
debit | credit | debit | Balance Sheet | NO |
| Contra Asset | Accumulated Depreciation | credit | debit | credit | Balance Sheet | NO |
| Liability |
Wages Payable
Taxes Payable Interest Payable ANY Payable Unearned Fees Unearned Rent Unearned ANYTHING |
credit | debit | credit | Balance Sheet | NO |
| Revenue |
Fees Earned
Rent Revenue |
credit | debit | credit | Income Statement | YES |
| Expense |
Wages Expense
Rent Expense Supplies Expense Insurance Expense Depreciation Expense Taxes Expense Interest Expense |
debit | credit | debit | Income Statement | YES |
Here are the 10 adjusting entries we will cover.
| Date | Account | Debit | Credit | ||
| 6/30 | Supplies Expense | 100 | ▲ Supplies Expense is an expense account that is increasing . | ||
| Supplies | 100 | ▼ Supplies is an asset account that is decreasing . | |||
| 6/30 | Insurance Expense | 100 | ▲ Insurance Expense is an expense account that is increasing . | ||
| Prepaid Insurance | 100 | ▼ Prepaid Insurance is an asset account that is decreasing . | |||
| 6/30 | Rent Expense | 100 | ▲ Rent Expense is an expense account that is increasing . | ||
| Prepaid Rent | 100 | ▼ Prepaid Rent is an asset account that is decreasing . | |||
| 6/30 | Taxes Expense | 100 | ▲ Taxes Expense is an expense account that is increasing . | ||
| Prepaid Taxes | 100 | ▼ Prepaid Taxes is an asset account that is decreasing . | |||
| 6/30 | Depreciation Expense | 100 | ▲ Depreciation Expense is an expense account that is increasing . | ||
| Accumulated Depreciation | 100 | ▲ Accumulated Depreciation is a contra asset account that is increasing . | |||
| 6/30 | Unearned Fees | 100 | ▼ Unearned Fees is a liability account that is decreasing . | ||
| Fees Earned | 100 | ▲ Fees Earned is a revenue account that is increasing . | |||
| 6/30 | Wages Expense | 100 | ▲ Wages Expense is an expense account that is increasing . | ||
| Wages Payable | 100 | ▲ Wages Payable is a liability account that is increasing . | |||
| 6/30 | Taxes Expense | 100 | ▲ Taxes Expense is an expense account that is increasing . | ||
| Taxes Payable | 100 | ▲ Taxes Payable is a liability account that is increasing . | |||
| 6/30 | Interest Expense | 100 | ▲ Interest Expense is an expense account that is increasing . | ||
| Interest Payable | 100 | ▲ Interest Payable is a liability account that is increasing . | |||
| 6/30 | Accounts Receivable | 100 | ▲ Accounts Receivable is an asset account that is increasing . | ||
| Fees Earned | 100 | ▲ Fees Earned is a revenue account that is increasing . | |||
From this point we will go into a more detailed discussion of each of these adjusting entries above.


11.7: Chapter Glossary and References
Chapter Glossary of Key Terms
Ascribed Status - a social status that is assignment to a person at birth or assumed in the course of their life
Social Network - social structure made of nodes and their relationships
Node - The people who are in your social network
Nationalities/Nationalism - sense of belonging to a particular nation that comes with birth (loyalty and devotion)
Marxism - the political and economic theories of Karl Marx and Friedrich Engels, later developed by their followers to form the basis for the theory and practice of materialism and communism.
Racialization - the social, economic, and political processes of transforming the population into races, creating the social construct of race.
Sociologist - The study of development, organization, and functioning of human society.
Counterculture - a subculture whose values and norms differ substantially from mainstream society
Rite of Passage - A life cycle ritual that marks a person's transition from one social state to another.
References
- http://community-wealth.org/strategies/panel/coops/index.html
- Omi, Michael & Howard Winant (1986). Racial formation in the United States: from the 1960s to the 1980s. Routledge & Kegan Paul. ISBN 0-7102-0970-3 .
- scholarworks.gvsu.edu/cgi/viewcontent.cgi?article=1009&context=gvjh
- Welsch, Robert Louis, and Luis Antonio Vivanco. Cultural Anthropology: Asking Questions about Humanity. New York: Oxford UP, 2015. Print.
- S. Dale Mclemore. Race and Ethnic Relations in America
- Joe R. Feagin. Systemic racism. http://books.google.com/books?id=z-v8_BkQ2n8C&pg=PA193&lpg=PA193&dq=systematic+racism+began+with+segregation&source=bl&ots=hcC8JhRupZ&sig=Fktl3IP7gpQTZVsolPv9MUhzDGI&hl=en&ei=6Qr5SZbkOKWEtAO67onGCg&sa=X&oi=book_result&ct=result&resnum=1
- S. Dale Mclemore. Racial and Ethnic Relations in America.
- http://journals.sagepub.com/doi/pdf/10.1177/002085238004700205
- http://www.history.com/topics/persian-gulf-war
Lee, Richard Borshay. Christmas in the Kalahari 1969, Natural History
CIA, CIA World Factbook. Feb. 17, 2009. 2 Mar 2009 < https://www.cia.gov/library/publications/the-world-factbook/index.html >.
Callaham, Terence. "Indian Caste System." 2 Mar 2009 < http://www.csuchico.edu/~cheinz/syllabi/asst001/spring98/india.htm >.
"Current Religious Based Conflicts." Center for Reduction of Religious Based Conflicts. 2009. Center For Reduction of Religious-Based Conflicts. 7 Mar 2009 < http://www.center2000.org/ >.
Dictionary.com. "Nationalism." March 5, 2009. http://dictionary.reference.com/browse/nationality?qsrc=2888
Dictionary.com. "Nation-State." March 5, 2009. http://dictionary.reference.com/browse/nation-state?qsrc=2888
Fassihi, Farnaz. Waiting for an Ordinary Day . New York: Public Affairs, 2008.
"The First Printed Currency: Massachusetts Bay - December 10, 1690." 2 Mar 2009 < http://www.coins.nd.edu/ColCurrency/CurrencyIntros/IntroEarliest.html >.
[4] Holsti, K. J. Resolving international conflicts : a taxonomy of behavior and some figures on procedures. Journal of Conflict Resolution, 10, 272-296.
[5] Hirshleifer, Jack. The Dark Side of the Force: Economic Foundations of Conflict Theory. Cambridge University Press, 2001.pg.2-9
[6] Schultz, Emily A., and Robert H. Lavenda. Cultural Anthropology : A Perspective on the Human Condition. New York: Oxford UP, Incorporated, 2009.pg.377-381.
Schultz, Emily A., and Robert H. Lavenda. Cultural Anthropology : A Perspective on the Human Condition. New York: Oxford UP, Incorporated, 2009.pg.244-245.
Callaham, Terence, and Roxanna Pavich. "India's Caste System." California State University, Chico—Chico State. 07 Mar. 2009 < http://www.csuchico.edu/~cheinz/syllabi/asst001/spring98/india.htm >.
[9] Tink. "A Glance At Recent Celebrity Treatment." Associated Content - associatedcontent.com. 5 Sept. 2007. 09 Mar. 2009 < https://archive.is/20130628113655/www.associatedcontent.com/article/364087/a_glance_at_recent_celebrity_treatment_pg3.html?cat=9 >.
[10] Krantz, Matt, and Chris Woodyard. "USATODAY.com - Stars live in a cushy world of special treatment." News, Travel, Weather, Entertainment, Sports, Technology, U.S. & World - USATODAY.com. 7 June 2004. USAToday. 09 Mar. 2009 < http://www.usatoday.com/money/advertising/2004-06-07-celebrity-treatment_x.htm >.
[14] The Free Online Dictionary. Farlex. 8 Mar. 2009 < http://www.thefreedictionary.com/ >.
[15] James, Paul. "Social Groups and Conflict." Blackboard. 2009. Western Washington University. 8 Mar. 2009 < http://www.wwu.edu >.
[16] Schultz, Emily A., and Robert H. Lavenda. Cultural Anthropology: A perspective on the Human Condition. Seventh Edition ed. New York: Oxford UP Inc., 2009. Pgs.291-292
[17] James, Paul. "Social Groups and Conflict." Blackboard. 2009. Western Washington University. 8 Mar. 2009 < http://www.wwu.edu >.
[18] Korry, Elaine. "A Fraternity Hazing Gone Wrong." 14 Nov. 2005. NPR. 8 Mar. 2009 < http://www.npr.org/templates/story/story.php?storyId=5012154 >.
[19] Dukcevich, Davide. "Best Fraternities For Future CEOs." Forbes. 13 Jan. 2003. 8 Mar. 2009 < http://www.forbes.com/2003/01/31/cx_dd_0131frat.html >.
[20] "Ku Klux Klan." The Columbia Encyclopedia. Sixth ed. Encyclopedia.com. 2008. 8 Mar. 2009 < http://www.encyclopedia.com/doc/1E1-KuKluxKl.html >.
[21] Business Dictionary. 8 Mar. 2009 < http://www.businessdictionary.com/definition/autonomous-work-group.html >.


10.4.15: Uncle Tom’s Cabin- The Good, The Bad, and the Ugly
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- Robin DeRosa, Abby Goode et al.
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After reading both “Benito Cereno” as well as The Heroic Slave , Harriet Beecher Stowe’s Uncle Tom’s Cabin provided a much deeper glance at the relationship held between slaves and their masters than the other two texts have thus far provided. The text features the complexity of the relationship held between the kindly Mr. Shelby and some of his most beloved slaves (Tom, Eliza, and her son Harry), while still showcasing more villainous slave owners, such as George’s (Eliza’s husband) master and Haley, the slave trader.
While “Benito Cereno” acted as more of a pro-slavery text, demonstrating through the plot’s uprising of the slaves that slaves are dangerous, unpredictable, and savage creatures, Uncle Tom’s Cabin definitely acts as an anti-slavery text by featuring the complex human emotions experienced by the slaves. Stowe instills sympathy within the reader by providing the background stories of each of the slaves, such as Tom’s good-natured and Christian tendencies, Eliza’s upbringing within the Shelby’s home as well as the loss of two children, and the manner in which her husband is essentially ripped away from her and their child’s lives simply because he is seen as another man’s property rather than an actual person. It truly makes you feel for this characters- similar to The Heroic Slave , except no slave revolts have actually occurred (yet) in which anyone is dying, which is a pro in my book.
Uncle Tom’s Cabin features slaves that are both painted as, and depending on the master, treated as a human being, as well as demonstrating the complexity of the slave owners themselves. For example, although Mr. Shelby has been forced into a financial position in which he must sell some of his most beloved slaves, he feels true sympathy towards these same slaves, worrying very much at what will become of them, as well as feeling as though he is betraying them- in Tom’s case, betraying the promise that he had once made of someday granting him his freedom, as well as betraying Eliza’s trust by ripping away her young and only child.
However, the text still features the much more usual and villainous slave owners, such as the trader, Haley, who at one point remarks to Mr. Shelby, “…you Kentucky folks spile your niggers. You mean well by ‘em, but ‘tan’t no real kindness, arter all. Now, a nigger, you see, what’s got to be hacked and tumbled round the world, and sold to Tom, and Dick, and the Lord knows who, ‘tan’t no kindness to be givin’ on him notions and expectations, and bringin’ on him up too well, for the rough and tumble comes all the harder on him after” (Chapter 1). Haley obviously sees slaves as pieces of property, and does not think that they should be brought up in the manner that Mr. Shelby has brought up his own slaves, seeing it as “spoiling” them for the exact same reason as the situation which is currently unfolding- at some point, these slaves will either be sold off for one reason or another, or their kind master will eventually die, leaving them to an unknown fate.
So while Uncle Tom’s Cabin exhibits many differences from the much more “pro-slavery” “Benito Cereno”, such as its anti-slavery message, it features multiple similarities with The Heroic Slave in the depiction of how both white and black characters are treated throughout the entirety of the text.


15.1: Why It Matters- The Research Process—Using and Citing Sources
Do you know how to use and cite sources?
In this module, you will learn how to use the words and ideas of others in your own writing.
Your authority as a thinker and writer is enhanced when you demonstrate your ability to engage in a conversation with the words and ideas of others. By using and integrating outside sources in a fair and attentive manner, you demonstrate that you have carefully researched and considered your topic. Your reader sees not only your ideas alone but also your points contextualized by the conversations of others. In this way, you establish yourself as one member of an intellectual community. A key component of properly integrating outside sources is also citing them appropriately. In this module, we’ll also examine documentation styles and learn about how to use both in-text and end-of-paper citations.
Contributors and Attributions
- Why It Matters: Using Sources. Provided by : University of Mississippi. License : CC BY: Attribution
- Drafting and Integrating. Provided by : Excelsior College. Located at : http://owl.excelsior.edu/research-and-citations/drafting-and-integrating/ . Project : Online Writing Lab. License : CC BY: Attribution
- Layers. Authored by : John Fowler. Located at : https://www.flickr.com/photos/snowpeak/12547422744/ . License : CC BY: Attribution


10.7: Appendicular Muscles of the Pelvic Girdle and Lower Limbs
By the end of this section, you will be able to:
- Identify the appendicular muscles of the pelvic girdle and lower limb
- Identify the movement and function of the pelvic girdle and lower limb
The appendicular muscles of the lower body position and stabilize the pelvic girdle , which serves as a foundation for the lower limbs. Comparatively, there is much more movement at the pectoral girdle than at the pelvic girdle. There is very little movement of the pelvic girdle because of its connection with the sacrum at the base of the axial skeleton. The pelvic girdle is less range of motion because it was designed to stabilize and support the body.
Muscles of the Thigh
What would happen if the pelvic girdle, which attaches the lower limbs to the torso, were capable of the same range of motion as the pectoral girdle? For one thing, walking would expend more energy if the heads of the femurs were not secured in the acetabula of the pelvis. The body’s center of gravity is in the area of the pelvis. If the center of gravity were not to remain fixed, standing up would be difficult as well. Therefore, what the leg muscles lack in range of motion and versatility, they make up for in size and power, facilitating the body’s stabilization, posture, and movement.
Gluteal Region Muscles That Move the Femur
Most muscles that insert on the femur (the thigh bone) and move it, originate on the pelvic girdle. The psoas major and iliacus make up the iliopsoas group . Some of the largest and most powerful muscles in the body are the gluteal muscles or gluteal group . The gluteus maximus is the largest; deep to the gluteus maximus is the gluteus medius , and deep to the gluteus medius is the gluteus minimus , the smallest of the trio (Figure \(\PageIndex{1}\) and Table \(\PageIndex{1}\)).
| Prime Mover | Origin | Insertion | Movement | Target | Target Motion Direction |
|---|---|---|---|---|---|
| Iliopsoas group | |||||
| Iliacus | Iliac fossa; iliac crest; lateral sacrum | Lesser trochanter of femur | Raises knee at hip, as if performing knee attack; assists lateral rotators in twisting thigh (and lower leg) outward; assists with bending over, maintaining posture | Femur |
Thigh: flexion; lateral rotation Torso: flexion |
| Psoas major | Lumbar vertebrae (L1 - L5); thoracic vertebrae (T12) | Lesser trochanter of femur | Raises knee at hip, as if performing knee attack; assists lateral rotators in twisting thigh (and lower leg) outward; assists with bending over, maintaining posture | Femur |
Thigh: flexion; lateral rotation Torso: flexion |
| Gluteal Group | |||||
| Gluteus maximus | Dorsal ilium; sacrum; coccyx | Gluteal tuberosity of femur; iliotibial tract | Lower knee and moves thigh back, as when getting ready to kick a ball | Femur | Extension |
| Gluteus medius | Lateral surface of ilium | Greater trochanter of femur | Opens thighs, as when doing a split | Femur | Abduction |
| Gluteus minimus | External surface of ilium | Greater trochanter of femur | Brings thighs back together | Femur | Abduction |
| Tensor fascia lata | Anterior aspect of iliac crest; anterior superior iliac spine | Iliotibial tract | Assists with raising the knee at hip and opening thighs; maintains posture by stabilizing the iliotibial tract, which connects to the knee | Femur | Flexion; abduction |
| Lateral Rotators | |||||
| Inferior gemellus | Ischial tuberosity | Greater trochanter of femur | Twists thigh (and lower leg) outward; maintains posture by stabilizing hip joint | Femur | Lateral rotation |
| Obturator externus | Outer surfaces of obturator membrane, pubis, and ischium; margins of obturator foramen | Trochanteric fossa of posterior femur | Twists thigh (and lower leg) outward; maintains posture by stabilizing hip joint | Femur | Lateral rotation |
| Obturator internus | Inner surface of obturator membrane; greater sciatic notch; margins of obturator foramen | Greater trochanter in front of piriformis | Twists thigh (and lower leg) outward; maintains posture by stabilizing hip joint | Femur | Lateral rotation |
| Piriformis | Anterolateral surface of sacrum | Greater trochanter of femur | Twists thigh (and lower leg) outward; maintains posture by stabilizing hip joint | Femur | Lateral rotation |
| Quadratus femoris | Ischial tuberosity | Trochanteric crest of femur | Twists thigh (and lower leg) outward; maintains posture by stabilizing hip joint | Femur | Lateral rotation |
| Superior gemellus | Ischial spine | Greater trochanter of femur | Twists thigh (and lower leg) outward; maintains posture by stabilizing hip joint | Femur | Lateral rotation |
| Adductors | |||||
| Adductor brevis | Body of pubis; inferior ramus of pubis | Linea aspera above adductor longus | Brings thighs back together; assists with raising knee | Femur | Adduction; flexion |
| Adductor longus | Pubis near pubic symphysis | Linea aspera | Brings thighs back together; assists with raising knee | Femur | Adduction; flexion |
| Adductor magnus | Ischial rami; pubic rami; ischial tuberosity | Linea aspera; adductor tubercle of femur | Brings thighs back together; assists with raising knee and moving thigh back | Femur | Adduction; flexion; extension |
| Pectineus | Pectineal line of pubis | Lesser trochanter to linea aspera of posterior aspect of femur | Opens thighs; assists with raising the knee and turning the thigh (and lower leg) inward | Femur | Adduction; flexion; medial rotation |
The tensor fascia latae is a thick, squarish muscle in the superior aspect of the lateral thigh. It acts as a synergist of the gluteus medius and iliopsoas in flexing and abducting the thigh. It also helps stabilize the lateral aspect of the knee by pulling on the iliotibial tract (band), making it taut. Deep to the gluteus maximus, the piriformis , obturator internus , obturator externus , superior gemellus , inferior gemellus , and quadratus femoris laterally rotate the femur at the hip.
The adductor longus , adductor brevis , and adductor magnus can both medially and laterally rotate the thigh depending on the placement of the foot. The adductor longus flexes the thigh, whereas the adductor magnus extends it. The pectineus adducts and flexes the femur at the hip as well. The pectineus is located in the femoral triangle , which is formed at the junction between the hip and the leg and also includes the femoral nerve, the femoral artery, the femoral vein, and the deep inguinal lymph nodes.
Thigh Muscles That Move the Femur, Tibia, and Fibula
Deep fascia in the thigh separates it into medial, anterior, and posterior compartments (Figure \(\PageIndex{1}\) and Table \(\PageIndex{2}\)). The muscles in the medial compartment of the thigh are responsible for adducting the femur at the hip. Along with the adductor longus, adductor brevis, adductor magnus, and pectineus, the strap-like gracilis adducts the thigh in addition to flexing the leg at the knee.
| Prime Mover | Origin | Insertion | Movement | Target | Target Motion Direction |
|---|---|---|---|---|---|
| Medial Compartment of Thigh | |||||
| Gracilis | Inferior ramus; body of pubis; ischial ramus | Medial surface of tibia | Moves back of lower legs up toward buttocks, as when kneeling; assists in opening thighs | Femur; tibia/fibula |
Thigh: adduction Lower leg: flexion |
| Anterior Compartment of Thigh: Quadricepts Femoris Group | |||||
| Rectus femoris | Anterior inferior iliac spine; superior margin of acetabulum | Patella; tibial tuberosity | Moves lower leg out in front of body, as when kicking; assists in raising knee | Femur; tibia/fibula |
Thigh: flexion Lower leg: extension |
| Sartorius | Anterior superior iliac spine | Medial aspect of proximal tibia | Moves back of lower legs up and back toward the buttocks, as when kneeling; assists in moving thigh diagonally upward and outward as when mounting a bike | Femur; tibia/fibula |
Thigh: flexion; abduction; lateral rotation Lower leg: flexion |
| Vastus intermedius | Proximal femur shaft | Patella; tibial tuberosity | Moves lower leg out in front of body, as when kicking | Tibia/fibula | Extension |
| Vastus lateralis | Greater trochanter; intertrochanteric line; linea apera | Patella; tibial tuberosity | Moves lower leg out in front of body, as when kicking | Tibia/fibula | Extension |
| Vastus medialis | Linea aspera; intertrochanteric line | Patella; tibial tuberosity | Moves lower leg out in front of body, as when kicking | Tibia/fibula | Extension |
| Posterior Compartment of Thigh: Hamstring Group | |||||
| Biceps femoris | Ischial tuberosity; linea aspera; distal femur | Head of fibula; lateral condyle of tibia | Moves back of lower legs up and back toward the buttocks, as when kneeling; moves thigh down and back; twists the thigh (and lower leg) outward | Femur; tibia/fibula |
Thigh: extension; lateral rotation Lower leg: flexion |
| Semimembranosus | Ischial tuberosity | Medial condyle of tibia; lateral condyle of femur | Moves back of lower legs up and back toward the buttocks, as when kneeling; moves thigh down and back; twists the thigh (and lower leg) outward | Femur; tibia/fibula |
Thigh: extension; medial rotation Lower leg: flexion |
| Semitendinosus | Ischial tuberosity | Upper tibial shaft | Moves back of lower legs up and back toward the buttocks, as when kneeling; moves thigh down and back; twists the thigh (and lower leg) outward | Femur; tibia/fibula |
Thigh: extension; medial rotation Lower leg: flexion |
The muscles of the anterior compartment of the thigh flex the thigh and extend the leg. This compartment contains the quadriceps femoris group , which actually comprises four muscles that extend and stabilize the knee. The rectus femoris is on the anterior aspect of the thigh, the vastus lateralis is on the lateral aspect of the thigh, the vastus medialis is on the medial aspect of the thigh, and the vastus intermedius is between the vastus lateralis and vastus medialis and deep to the rectus femoris. The tendon common to all four is the quadriceps tendon (patellar tendon), which inserts into the patella and continues below it as the patellar ligament . The patellar ligament attaches to the tibial tuberosity. In addition to the quadriceps femoris, the sartorius is a band-like muscle that extends from the anterior superior iliac spine to the medial side of the proximal tibia. This versatile muscle flexes the leg at the knee and flexes, abducts, and laterally rotates the leg at the hip. This muscle allows us to sit cross-legged.
The posterior compartment of the thigh includes muscles that flex the leg and extend the thigh. The three long muscles on the back of the knee are the hamstring group , which flexes the knee. These are the biceps femoris , semitendinosus , and semimembranosus . The tendons of these muscles form the popliteal fossa , the diamond-shaped space at the back of the knee.
Muscles That Move the Feet and Toes
Similar to the thigh muscles, the muscles of the leg are divided by deep fascia into compartments, although the leg has three: anterior, lateral, and posterior (Figure \(\PageIndex{2}\) and Table \(\PageIndex{3}\)).
| Prime Mover | Origin | Insertion | Movement | Target | Target Motion Direction |
|---|---|---|---|---|---|
| Anterior Compartment of Leg | |||||
| Extensor digitorum longus | Lateral condyle of tibia; proximal portion of fibula; interosseous membrane | Middle and distal phalanges of toes 2 - 5 | Raises the sole of the foot off the ground, as when preparing to foot-tap; extends toes | Foot; toes 2 - 5 |
Foot: dorsiflexion Toes: extension |
| Extensor hallucis longus | Anteromedial fibula shaft; interosseous membrane | Distal phalanx hallux (big toe) | Raises the sole of the foot off the ground, as when preparing to foot-tap; extends the big toe | Foot; big toe |
Foot: dorsiflexion Big toe: extension |
| Tibialis anterior | Lateral condyle and upper tibial shaft; interosseous membrane | Interior surface of medial cuneiform; first metatarsal bone | Raises the sole of the foot off the ground as when preparing to foot-tap; bends the inside of the foot upwards, as when catching your balance while falling laterally toward the opposite side as the balancing foot | Foot | Dorsiflexion; inversion |
| Lateral Compartment of Leg | |||||
| Fibularis (peroneus) brevis | Distal fibula shaft | Proximal end of fifth metatarsal | Lowers the sole of the foot to the ground as when foot-tapping or jumping; bends the inside of the foot downward, as when catching your balance while falling laterally toward the same side as the balancing foot | Foot | Plantar flexion; eversion |
| Fibularis longus | Upper portion of lateral fibula | First metatarsal; medial cuneiform | Lowers the sole of the foot to the ground as when foot-tapping or jumping; bends the inside of the foot downward, as when catching your balance while falling laterally toward the same side as the balancing foot | Foot | Plantar flexion; eversion |
| Posterior Compartment of Leg: Superficial Muscles | |||||
| Gastrocnemius | Medial and lateral condyles of femur | Posterior calcaneus | Lowers the sole of the foot to the ground, as when foot-tapping or jumping; assists in moving the back of the lower legs up and back toward the buttocks | Foot; tibia/fibula |
Foot: plantar flexion Tibia/fibula: flexion |
| Plantaris | Posterior femur above lateral condyle | Calcaneus or calcaneus tendon | Lowers the sole of the foot to the ground, as when foot-tapping or jumping; assists in moving the back of the lower legs up and back toward the buttocks | Foot; tibia/fibula |
Foot: plantar flexion Tibia/fibula: flexion |
| Soleus | Superior tibia; fibula; interosseous membrane | Posterior calcaneus | Lowers the sole of the foot to the ground, as when foot-tapping or jumping; maintains posture while walking | Foot | Plantar flexion |
| Tibialis posterior | Superior tibia; fibula; interosseous membrane | Several tarsals and metatarsals 2 - 4 | Lowers the sole of the foot to the ground, as when foot-tapping or jumping | Foot | Plantar flexion |
| Posterior Compartment of Leg: Deep Muscles | |||||
| Flexor digitorum longus | Posterior tibia | Distal phalanges of toes 2 - 5 | Lowers the sole of the foot to the ground, as when foot-tapping or jumping; bends the inside of the foot upward and flexes toes | Foot; toes 2 - 5 |
Foot: plantar flexion; inversion Toes: flexion |
| Flexor hallucis longus | Midshaft of fibula; interosseous membrane | Distal phalanx of hallux (big toe) | Flexes big toe | Foot; big toe |
Foot: plantar flexion Big toe: flexion |
| Popliteus | Lateral condyle of femur; lateral meniscus | Proximal tibia | Moves the back of the lower legs up and back toward buttocks; assists in rotation of the leg at the knee and thigh | Tibia/fibula |
Tibia/fibula: flexion Thigh and lower leg: medial and lateral rotation |
The muscles in the anterior compartment of the leg : the tibialis anterior , a long and thick muscle on the lateral surface of the tibia, the extensor hallucis longus , deep under it, and the extensor digitorum longus , lateral to it, all contribute to raising the front of the foot when they contract. The fibularis tertius , a small muscle that originates on the anterior surface of the fibula, is associated with the extensor digitorum longus and sometimes fused to it, but is not present in all people. Thick bands of connective tissue called the superior extensor retinaculum (transverse ligament of the ankle) and the inferior extensor retinaculum , hold the tendons of these muscles in place during dorsiflexion.
The lateral compartment of the leg includes two muscles: the fibularis longus (peroneus longus) and the fibularis brevis (peroneus brevis). The superficial muscles in the posterior compartment of the leg all insert onto the calcaneal tendon (Achilles tendon), a strong tendon that inserts into the calcaneal bone of the ankle. The muscles in this compartment are large and strong and keep humans upright. The most superficial and visible muscle of the calf is the gastrocnemius . Deep to the gastrocnemius is the wide, flat soleus . The plantaris runs obliquely between the two; some people may have two of these muscles, whereas no plantaris is observed in about seven percent of other cadaver dissections. The plantaris tendon is a desirable substitute for the fascia lata in hernia repair, tendon transplants, and repair of ligaments. There are four deep muscles in the posterior compartment of the leg as well: the popliteus , flexor digitorum longus , flexor hallucis longus , and tibialis posterior .
The foot also has intrinsic muscles, which originate and insert within it (similar to the intrinsic muscles of the hand). These muscles primarily provide support for the foot and its arch, and contribute to movements of the toes (Figure \(\PageIndex{3}\) and Table \(\PageIndex{4}\)). The principal support for the longitudinal arch of the foot is a deep fascia called plantar aponeurosis , which runs from the calcaneus bone to the toes (inflammation of this tissue is the cause of “plantar fasciitis,” which can affect runners. The intrinsic muscles of the foot consist of two groups. The dorsal group includes only one muscle, the extensor digitorum brevis . The second group is the plantar group , which consists of four layers, starting with the most superficial.
| Prime Mover | Origin | Insertion | Movement | Target | Target Motion Direction |
|---|---|---|---|---|---|
| Dorsal Group | |||||
| Extensor digitorum brevis | Calcaneus; extensor retinaculum | Base of proximal phalanx of big toe; extensor expansions on toes 2 - 5 | Extends toes 2 - 5 | Toes 2 - 5 | Extension |
| Plantar Group: Layer 1 | |||||
| Abductor digiti minimi | Calcaneal tuberosity | Proximal phalanx of toe 5 (pinky toe) | Abducts and flexes toe 5 | Toe 5 | Abduction; flexion |
| Abductor hallucis | Calcaneal tuberosity; flexor retinaculum | Proximal phalanx of hallux (big toe) | Abducts and flexes big toe | Big toe | Abduction; flexion |
| Flexor digitorum brevis | Calcaneal tuberosity | Middle phalanx of toes 2 - 4 | Flexes toes 2 - 4 | Middle toes | Flexion |
| Plantar Group: Layer 2 | |||||
| Lumbricals | tendons of flexor digitorum longus | Medial side of proximal phalanx of toes 2 - 5 | Extends toes 2 - 5 at the interphalangeal joints; flexes the small toes at the metatarsophalangeal joints | Toes 2 - 5 | Extension; flexion |
| Quadratus plantae | Medial and lateral sides of calcaneus | Tendon of flexor digitorum longus | Assists in flexing toes 2 - 5 | Toes 2 - 5 | Flexion |
| Plantar Group: Layer 3 | |||||
| Adductor hallucis | Bases of metatarsals 2 - 4; fibularis longus tendon sheath; ligament across metatarsophalangeal joints | Base of proximal phalanx of hallux (big toe) | Adducts and flexes big toe | Big toe | Adduction; flexion |
| Flexor digiti minimi brevis | Base of metatarsal 5; tendon sheath of fibularis longus | Base of proximal phalanx of toe 5 (pinky toe) | Flexes pinky toe | Pinky toe | Flexion |
| Flexor hallicus brevis | Lateral cuneiform; cuboid bones | Base of proximal phalanx of hallux (big toe) | Flexes big toe | Big toe | Flexion |
| Plantar Group: Layer 4 | |||||
| Dorsal interossei | Sides of metatarsals | Both sides of toe 2; for each other toe, extensor expansion over first phalanx on side opposite toe 2 | Abducts and flexes middle toes at metatarsophalangeal joints; extends middle toes at interphalangeal joints | Middle toes | Abduction; flexion; extension |
| Plantar interossei | Side of each metatarsal that faces metatarsal 2 (absent from metatarsal 2) | Extensor expansion on first phalanx of each tow ( except on 2) on side facing toe 2 | Abducts toes 3 - 5; flexes proximal phalanges and extends distal phalanges | Small toes | Abduction; flexion; extension |
Concept Review
The pelvic girdle attaches the legs to the axial skeleton. The hip joint is where the pelvic girdle and the leg come together. The hip is joined to the pelvic girdle by many muscles. In the gluteal region, the psoas major and iliacus form the iliopsoas. The large and strong gluteus maximus, gluteus medius, and gluteus minimus extend and abduct the femur. Along with the gluteus maximus, the tensor fascia lata muscle forms the iliotibial tract. The lateral rotators of the femur at the hip are the piriformis, obturator internus, obturator externus, superior gemellus, inferior gemellus, and quadratus femoris. On the medial part of the thigh, the adductor longus, adductor brevis, and adductor magnus adduct the thigh and medially rotate it. The pectineus muscle adducts and flexes the femur at the hip.
The thigh muscles that move the femur, tibia, and fibula are divided into medial, anterior, and posterior compartments. The medial compartment includes the adductors, pectineus, and the gracilis. The anterior compartment comprises the quadriceps femoris, quadriceps tendon, patellar ligament, and the sartorius. The quadriceps femoris is made of four muscles: the rectus femoris, the vastus lateralis, the vastus medius, and the vastus intermedius, which together extend the knee. The posterior compartment of the thigh includes the hamstrings: the biceps femoris, semitendinosus, and the semimembranosus, which all flex the knee.
The muscles of the leg that move the foot and toes are divided into anterior, lateral, superficial- and deep-posterior compartments. The anterior compartment includes the tibialis anterior, the extensor hallucis longus, the extensor digitorum longus, and the fibularis (peroneus) tertius. The lateral compartment houses the fibularis (peroneus) longus and the fibularis (peroneus) brevis. The superficial posterior compartment has the gastrocnemius, soleus, and plantaris; and the deep posterior compartment has the popliteus, tibialis posterior, flexor digitorum longus, and flexor hallucis longus.
Review Questions
Q. The large muscle group that attaches the leg to the pelvic girdle and produces extension of the hip joint is the ________ group.
A. gluteal
B. obturator
C. adductor
D. abductor
- Answer
-
Answer: A
Q. Which muscle produces movement that allows you to cross your legs?
A. the gluteus maximus
B. the piriformis
C. the gracilis
D. the sartorius
- Answer
-
Answer: D
Q. What is the largest muscle in the lower leg?
A. soleus
B. gastrocnemius
C. tibialis anterior
D. tibialis posterior
- Answer
-
Answer: B
Q. The vastus intermedius muscle is deep to which of the following muscles?
A. biceps femoris
B. rectus femoris
C. vastus medialis
D. vastus lateralis
- Answer
-
Answer: B
Critical Thinking Questions
Q. Which muscles form the hamstrings? How do they function together?
- Answer
-
A. The biceps femoris, semimembranosus, and semitendinosus form the hamstrings. The hamstrings flex the leg at the knee joint.
Q. Which muscles form the quadriceps? How do they function together?
- Answer
-
A. The rectus femoris, vastus medialis, vastus lateralis, and vastus intermedius form the quadriceps. The quadriceps muscles extend the leg at the knee joint.
Glossary
- adductor brevis
- muscle that adducts and medially rotates the thigh
- adductor longus
- muscle that adducts, medially rotates, and flexes the thigh
- adductor magnus
- muscle with an anterior fascicle that adducts, medially rotates and flexes the thigh, and a posterior fascicle that assists in thigh extension
- anterior compartment of the leg
- region that includes muscles that dorsiflex the foot
- anterior compartment of the thigh
- region that includes muscles that flex the thigh and extend the leg
- biceps femoris
- hamstring muscle
- calcaneal tendon
- (also, Achilles tendon) strong tendon that inserts into the calcaneal bone of the ankle
- dorsal group
- region that includes the extensor digitorum brevis
- extensor digitorum brevis
- muscle that extends the toes
- extensor digitorum longus
- muscle that is lateral to the tibialis anterior
- extensor hallucis longus
- muscle that is partly deep to the tibialis anterior and extensor digitorum longus
- femoral triangle
- region formed at the junction between the hip and the leg and includes the pectineus, femoral nerve, femoral artery, femoral vein, and deep inguinal lymph nodes
- fibularis brevis
- (also, peroneus brevis) muscle that plantar flexes the foot at the ankle and everts it at the intertarsal joints
- fibularis longus
- (also, peroneus longus) muscle that plantar flexes the foot at the ankle and everts it at the intertarsal joints
- fibularis tertius
- small muscle that is associated with the extensor digitorum longus
- flexor digitorum longus
- muscle that flexes the four small toes
- flexor hallucis longus
- muscle that flexes the big toe
- gastrocnemius
- most superficial muscle of the calf
- gluteal group
- muscle group that extends, flexes, rotates, adducts, and abducts the femur
- gluteus maximus
- largest of the gluteus muscles that extends the femur
- gluteus medius
- muscle deep to the gluteus maximus that abducts the femur at the hip
- gluteus minimus
- smallest of the gluteal muscles and deep to the gluteus medius
- gracilis
- muscle that adducts the thigh and flexes the leg at the knee
- hamstring group
- three long muscles on the back of the leg
- iliacus
- muscle that, along with the psoas major, makes up the iliopsoas
- iliopsoas group
- muscle group consisting of iliacus and psoas major muscles, that flexes the thigh at the hip, rotates it laterally, and flexes the trunk of the body onto the hip
- iliotibial tract
- muscle that inserts onto the tibia; made up of the gluteus maximus and connective tissues of the tensor fasciae latae
- inferior extensor retinaculum
- cruciate ligament of the ankle
- inferior gemellus
- muscle deep to the gluteus maximus on the lateral surface of the thigh that laterally rotates the femur at the hip
- lateral compartment of the leg
- region that includes the fibularis (peroneus) longus and the fibularis (peroneus) brevis and their associated blood vessels and nerves
- medial compartment of the thigh
- a region that includes the adductor longus, adductor brevis, adductor magnus, pectineus, gracilis, and their associated blood vessels and nerves
- obturator externus
- muscle deep to the gluteus maximus on the lateral surface of the thigh that laterally rotates the femur at the hip
- obturator internus
- muscle deep to the gluteus maximus on the lateral surface of the thigh that laterally rotates the femur at the hip
- patellar ligament
- extension of the quadriceps tendon below the patella
- pectineus
- muscle that abducts and flexes the femur at the hip
- pelvic girdle
- hips, a foundation for the lower limb
- piriformis
- muscle deep to the gluteus maximus on the lateral surface of the thigh that laterally rotates the femur at the hip
- plantar aponeurosis
- muscle that supports the longitudinal arch of the foot
- plantar group
- four-layered group of intrinsic foot muscles
- plantaris
- muscle that runs obliquely between the gastrocnemius and the soleus
- popliteal fossa
- diamond-shaped space at the back of the knee
- popliteus
- muscle that flexes the leg at the knee and creates the floor of the popliteal fossa
- posterior compartment of the leg
- region that includes the superficial gastrocnemius, soleus, and plantaris, and the deep popliteus, flexor digitorum longus, flexor hallucis longus, and tibialis posterior
- posterior compartment of the thigh
- region that includes muscles that flex the leg and extend the thigh
- psoas major
- muscle that, along with the iliacus, makes up the iliopsoas
- quadratus femoris
- muscle deep to the gluteus maximus on the lateral surface of the thigh that laterally rotates the femur at the hip
- quadriceps femoris group
- four muscles, that extend and stabilize the knee
- quadriceps tendon
- (also, patellar tendon) tendon common to all four quadriceps muscles, inserts into the patella
- rectus femoris
- quadricep muscle on the anterior aspect of the thigh
- sartorius
- band-like muscle that flexes, abducts, and laterally rotates the leg at the hip
- semimembranosus
- hamstring muscle
- semitendinosus
- hamstring muscle
- soleus
- wide, flat muscle deep to the gastrocnemius
- superior extensor retinaculum
- transverse ligament of the ankle
- superior gemellus
- muscle deep to the gluteus maximus on the lateral surface of the thigh that laterally rotates the femur at the hip
- tensor fascia lata
- muscle that flexes and abducts the thigh
- tibialis anterior
- muscle located on the lateral surface of the tibia
- tibialis posterior
- muscle that plantar flexes and inverts the foot
- vastus intermedius
- quadricep muscle that is between the vastus lateralis and vastus medialis and is deep to the rectus femoris
- vastus lateralis
- quadricep muscle on the lateral aspect of the thigh
- vastus medialis
- quadricep muscle on the medial aspect of the thigh
Contributors and Attributions
-
OpenStax Anatomy & Physiology (CC BY 4.0). Access for free at https://openstax.org/books/anatomy-and-physiology


14.1: Introduction
Chapter Objectives
After studying this chapter, you will be able to:
- Describe the components of the somatic nervous system
- Name the modalities and submodalities of the sensory systems
- Distinguish between general and special senses
- Describe regions of the central nervous system that contribute to somatic functions
- Explain the stimulus-response motor pathway
The somatic nervous system is traditionally considered a division within the peripheral nervous system. However, this misses an important point: somatic refers to a functional division, whereas peripheral refers to an anatomic division. The somatic nervous system is responsible for our conscious perception of the environment and for our voluntary responses to that perception by means of skeletal muscles. Peripheral sensory neurons receive input from environmental stimuli, but the neurons that produce motor responses originate in the central nervous system. The distinction between the structures (i.e., anatomy) of the peripheral and central nervous systems and functions (i.e., physiology) of the somatic and autonomic systems can most easily be demonstrated through a simple reflex action.  Sensory receptors in the skin sense extreme temperature and the early signs of tissue damage. This triggers an action potential, which travels along the sensory fiber from the skin, through the dorsal spinal root to the spinal cord, and directly activates a ventral horn motor neuron. That neuron sends a signal along its axon to excite the biceps brachii, causing contraction of the muscle and flexion of the forearm at the elbow to withdraw the hand from the hot stove. The withdrawal reflex has more components, such as inhibiting the opposing muscle and balancing posture while the arm is forcefully withdrawn, which will be further explored at the end of this chapter.
The basic withdrawal reflex explained above includes sensory input (the painful stimulus), central processing (the synapse in the spinal cord), and motor output (activation of a ventral motor neuron that causes contraction of the biceps brachii). Expanding the explanation of the withdrawal reflex can include inhibition of the opposing muscle, or cross extension, either of which increase the complexity of the example by involving more central neurons. A collateral branch of the sensory axon would inhibit another ventral horn motor neuron so that the triceps brachii do not contract and slow the withdrawal down. The cross extensor reflex provides a counterbalancing movement on the other side of the body, which requires another collateral of the sensory axon to activate contraction of the extensor muscles in the contralateral limb.
A more complex example of somatic function is conscious muscle movement. For example, reading of this text starts with visual sensory input to the retina, which then projects to the thalamus, and on to the cerebral cortex. A sequence of regions of the cerebral cortex process the visual information, starting in the primary visual cortex of the occipital lobe, and resulting in the conscious perception of these letters. Subsequent cognitive processing results in understanding of the content. As you continue reading, regions of the cerebral cortex in the frontal lobe plan how to move the eyes to follow the lines of text. The output from the cortex causes activity in motor neurons in the brain stem that cause movement of the extraocular muscles through the third, fourth, and sixth cranial nerves. This example also includes sensory input (the retinal projection to the thalamus), central processing (the thalamus and subsequent cortical activity), and motor output (activation of neurons in the brain stem that lead to coordinated contraction of extraocular muscles).


9: Hypothesis Testing with One Sample
One job of a statistician is to make statistical inferences about populations based on samples taken from the population. Confidence intervals are one way to estimate a population parameter. Another way to make a statistical inference is to make a decision about a parameter. For instance, a car dealer advertises that its new small truck gets 35 miles per gallon, on average. A tutoring service claims that its method of tutoring helps 90% of its students get an A or a B. A company says that women managers in their company earn an average of $60,000 per year.
-
- 9.1: Prelude to Hypothesis Testing
- A statistician will make a decision about claims via a process called "hypothesis testing." A hypothesis test involves collecting data from a sample and evaluating the data. Then, the statistician makes a decision as to whether or not there is sufficient evidence, based upon analysis of the data, to reject the null hypothesis.
-
- 9.2: Null and Alternative Hypotheses
- The actual test begins by considering two hypotheses. They are called the null hypothesis and the alternative hypothesis. These hypotheses contain opposing viewpoints. Since the null and alternative hypotheses are contradictory, you must examine evidence to decide if you have enough evidence to reject the null hypothesis or not.
-
- 9.3: Outcomes and the Type I and Type II Errors
- In every hypothesis test, the outcomes are dependent on a correct interpretation of the data. Incorrect calculations or misunderstood summary statistics can yield errors that affect the results. A Type I error occurs when a true null hypothesis is rejected. A Type II error occurs when a false null hypothesis is not rejected.
-
- 9.4: Distribution Needed for Hypothesis Testing
- When testing for a single population mean: A Student's t-test should be used if the data come from a simple, random sample and the population is approximately normally distributed, or the sample size is large, with an unknown standard deviation. The normal test will work if the data come from a simple, random sample and the population is approximately normally distributed, or the sample size is large, with a known standard deviation.
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- 9.5: Rare Events, the Sample, Decision and Conclusion
- When the probability of an event occurring is low, and it happens, it is called a rare event. Rare events are important to consider in hypothesis testing because they can inform your willingness not to reject or to reject a null hypothesis. To test a null hypothesis, find the p-value for the sample data and graph the results.
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- 9.6: Additional Information and Full Hypothesis Test Examples
- The hypothesis test itself has an established process. This can be summarized as follows: Determine H0 and Ha. Remember, they are contradictory. Determine the random variable. Determine the distribution for the test. Draw a graph, calculate the test statistic, and use the test statistic to calculate the p-value. (A z-score and a t-score are examples of test statistics.) Compare the preconceived α with the p-value, make a decision (reject or do not reject H0), and write a clear conclusion.
Contributors and Attributions
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Barbara Illowsky and Susan Dean (De Anza College) with many other contributing authors. Content produced by OpenStax College is licensed under a Creative Commons Attribution License 4.0 license. Download for free at<EMAIL_ADDRESS>.


14.3: Staining Microscopic Specimens and Descriptions
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Learning Objectives
- Differentiate between simple and differential stains
- Describe the unique features of commonly used stains
- Explain the procedures and name clinical applications for Gram, endospore, acid-fast, negative capsule, and flagella staining
- What to describe about cells under the microscope
Clinical Focus: part 2
Wound infections like Cindy’s can be caused by many different types of bacteria, some of which can spread rapidly with serious complications. Identifying the specific cause is very important to select a medication that can kill or stop the growth of the bacteria.
After calling a local doctor about Cindy’s case, the camp nurse sends the sample from the wound to the closest medical laboratory. Unfortunately, since the camp is in a remote area, the nearest lab is small and poorly equipped. A more modern lab would likely use other methods to culture, grow, and identify the bacteria, but in this case, the technician decides to make a wet mount from the specimen and view it under a brightfield microscope. In a wet mount, a small drop of water is added to the slide, and a cover slip is placed over the specimen to keep it in place before it is positioned under the objective lens.
Under the brightfield microscope, the technician can barely see the bacteria cells because they are nearly transparent against the bright background. To increase contrast, the technician inserts an opaque light stop above the illuminator. The resulting darkfield image clearly shows that the bacteria cells are spherical and grouped in clusters, like grapes.
Exercise \(\PageIndex{1}\)
- Why is it important to identify the shape and growth patterns of cells in a specimen?
- What other types of microscopy could be used effectively to view this specimen?
In their natural state, most of the cells and microorganisms that we observe under the microscope lack color and contrast. This makes it difficult, if not impossible, to detect important cellular structures and their distinguishing characteristics without artificially treating specimens. We have already alluded to certain techniques involving stains and fluorescent dyes, and in this section we will discuss specific techniques for sample preparation in greater detail. Indeed, numerous methods have been developed to identify specific microbes, cellular structures, DNA sequences, or indicators of infection in tissue samples, under the microscope. Here, we will focus on the most clinically relevant techniques.
Preparing Specimens for Light Microscopy
In clinical settings, light microscopes are the most commonly used microscopes. There are two basic types of preparation used to view specimens with a light microscope: wet mounts and fixed specimens.
The simplest type of preparation is the wet mount, in which the specimen is placed on the slide in a drop of liquid. Some specimens, such as a drop of urine, are already in a liquid form and can be deposited on the slide using a dropper. Solid specimens, such as a skin scraping, can be placed on the slide before adding a drop of liquid to prepare the wet mount. Sometimes the liquid used is simply water, but often stains are added to enhance contrast. Once the liquid has been added to the slide, a coverslip is placed on top and the specimen is ready for examination under the microscope.
The second method of preparing specimens for light microscopy is fixation. The “fixing” of a sample refers to the process of attaching cells to a slide. Fixation is often achieved either by heating (heat fixing) or chemically treating the specimen. In addition to attaching the specimen to the slide, fixation also kills microorganisms in the specimen, stopping their movement and metabolism while preserving the integrity of their cellular components for observation.
To heat-fix a sample, a thin layer of the specimen is spread on the slide (called a smear), and the slide is then briefly heated over a heat source (Figure \(\PageIndex{1}\)). Chemical fixatives are often preferable to heat for tissue specimens. Chemical agents such as acetic acid, ethanol, methanol, formaldehyde (formalin), and glutaraldehyde can denature proteins, stop biochemical reactions, and stabilize cell structures in tissue samples (Figure \(\PageIndex{1}\)).
In addition to fixation, staining is almost always applied to color certain features of a specimen before examining it under a light microscope. Stains, or dyes, contain salts made up of a positive ion and a negative ion. Depending on the type of dye, the positive or the negative ion may be the chromophore (the colored ion); the other, uncolored ion is called the counterion. If the chromophore is the positively charged ion, the stain is classified as a basic dye; if the negative ion is the chromophore, the stain is considered an acidic dye.
Dyes are selected for staining based on the chemical properties of the dye and the specimen being observed, which determine how the dye will interact with the specimen. In most cases, it is preferable to use a positive stain, a dye that will be absorbed by the cells or organisms being observed, adding color to objects of interest to make them stand out against the background. However, there are scenarios in which it is advantageous to use a negative stain, which is absorbed by the background but not by the cells or organisms in the specimen. Negative staining produces an outline or silhouette of the organisms against a colorful background (Figure \(\PageIndex{2}\)).
Because cells typically have negatively charged cell walls, the positive chromophores in basic dyes tend to stick to the cell walls, making them positive stains. Thus, commonly used basic dyes such as basic fuchsin, crystal violet, malachite green, methylene blue, and safranin typically serve as positive stains. On the other hand, the negatively charged chromophores in acidic dyes are repelled by negatively charged cell walls, making them negative stains. Commonly used acidic dyes include acid fuchsin, eosin, and rose bengal.
Some staining techniques involve the application of only one dye to the sample; others require more than one dye. In simple staining, a single dye is used to emphasize particular structures in the specimen. A simple stain will generally make all of the organisms in a sample appear to be the same color, even if the sample contains more than one type of organism. In contrast, differential staining distinguishes organisms based on their interactions with multiple stains. In other words, two organisms in a differentially stained sample may appear to be different colors. Differential staining techniques commonly used in clinical settings include Gram staining, acid-fast staining, endospore staining, flagella staining, and capsule staining.
Exercise \(\PageIndex{2}\)
- Explain why it is important to fix a specimen before viewing it under a light microscope.
- What types of specimens should be chemically fixed as opposed to heat-fixed?
- Why might an acidic dye react differently with a given specimen than a basic dye?
- Explain the difference between a positive stain and a negative stain.
- Explain the difference between simple and differential staining.
Gram Staining
The Gram stain procedure is a differential staining procedure that involves multiple steps. It was developed by Danish microbiologist Hans Christian Gram in 1884 as an effective method to distinguish between bacteria with different types of cell walls, and even today it remains one of the most frequently used staining techniques. The steps of the Gram stain procedure are illustrated in Figure \(\PageIndex{3}\) and listed below.
- First, crystal violet, a primary stain, is applied to a heat-fixed smear, giving all of the cells a purple color.
- Next, Gram’s iodine, a mordant, is added. A mordant is a substance used to set or stabilize stains or dyes; in this case, Gram’s iodine acts like a trapping agent that complexes with the crystal violet, making the crystal violet–iodine complex clump and stay contained in thick layers of peptidoglycan in the cell walls.
- Next, a decolorizing agent is added, usually ethanol or an acetone/ethanol solution. Cells that have thick peptidoglycan layers in their cell walls are much less affected by the decolorizing agent; they generally retain the crystal violet dye and remain purple. However, the decolorizing agent more easily washes the dye out of cells with thinner peptidoglycan layers, making them again colorless.
- Finally, a secondary counterstain, usually safranin, is added. This stains the decolorized cells pink and is less noticeable in the cells that still contain the crystal violet dye.
The purple, crystal-violet stained cells are referred to as gram-positive cells, while the red, safranin-dyed cells are gram-negative (Figure \(\PageIndex{4}\)). However, there are several important considerations in interpreting the results of a Gram stain. First, older bacterial cells may have damage to their cell walls that causes them to appear gram-negative even if the species is gram-positive. Thus, it is best to use fresh bacterial cultures for Gram staining. Second, errors such as leaving on decolorizer too long can affect the results. In some cases, most cells will appear gram-positive while a few appear gram-negative (as in Figure \(\PageIndex{4}\)). This suggests damage to the individual cells or that decolorizer was left on for too long; the cells should still be classified as gram-positive if they are all the same species rather than a mixed culture.
Besides their differing interactions with dyes and decolorizing agents, the chemical differences between gram-positive and gram-negative cells have other implications with clinical relevance. For example, Gram staining can help clinicians classify bacterial pathogens in a sample into categories associated with specific properties. Gram-negative bacteria tend to be more resistant to certain antibiotics than gram-positive bacteria. We will discuss this and other applications of Gram staining in more detail in later chapters.
Exercise \(\PageIndex{3}\)
- Explain the role of Gram’s iodine in the Gram stain procedure.
- Explain the role of alcohol in the Gram stain procedure.
- What color are gram-positive and gram-negative cells, respectively, after the Gram stain procedure?
Clinical Focus: Part 3
Viewing Cindy’s specimen under the darkfield microscope has provided the technician with some important clues about the identity of the microbe causing her infection. However, more information is needed to make a conclusive diagnosis. The technician decides to make a Gram stain of the specimen. This technique is commonly used as an early step in identifying pathogenic bacteria. After completing the Gram stain procedure, the technician views the slide under the brightfield microscope and sees purple, grape-like clusters of spherical cells (Figure \(\PageIndex{5}\)).
Figure \(\PageIndex{5}\): Cindy's specimen (credit: modification of work by American Society for Microbiology)
Exercise \(\PageIndex{4}\)
- Are these bacteria gram-positive or gram-negative?
- What does this reveal about their cell walls?
Acid-Fast Stains
Acid-fast staining is another commonly used, differential staining technique that can be an important diagnostic tool. An acid-fast stain is able to differentiate two types of gram-positive cells: those that have waxy mycolic acids in their cell walls, and those that do not. Two different methods for acid-fast staining are the Ziehl-Neelsen technique and the Kinyoun technique. Both use carbol-fuchsin as the primary stain. The waxy, acid-fast cells retain the carbol-fuchsin even after a decolorizing agent (an acid-alcohol solution) is applied. A secondary counterstain, methylene blue, is then applied, which renders non–acid-fast cells blue.
The fundamental difference between the two carbol-fuchsin-based methods is whether heat is used during the primary staining process. The Ziehl-Neelsen method uses heat to infuse the carbol-fuchsin into the acid-fast cells, whereas the Kinyoun method does not use heat. Both techniques are important diagnostic tools because a number of specific diseases are caused by acid-fast bacteria (AFB). If AFB are present in a tissue sample, their red or pink color can be seen clearly against the blue background of the surrounding tissue cells (Figure \(\PageIndex{6}\)).
Exercise \(\PageIndex{5}\)
Why are acid-fast stains useful?
Using Microscopy to Diagnose Tuberculosis
Mycobacterium tuberculosis , the bacterium that causes tuberculosis, can be detected in specimens based on the presence of acid-fast bacilli. Often, a smear is prepared from a sample of the patient’s sputum and then stained using the Ziehl-Neelsen technique (Figure \(\PageIndex{6}\)). If acid-fast bacteria are confirmed, they are generally cultured to make a positive identification. Variations of this approach can be used as a first step in determining whether M. tuberculosis or other acid-fast bacteria are present, though samples from elsewhere in the body (such as urine) may contain other Mycobacterium species.
An alternative approach for determining the presence of M. tuberculosis is immunofluorescence. In this technique, fluorochrome-labeled antibodies bind to M. tuberculosis , if present. Antibody-specific fluorescent dyes can be used to view the mycobacteria with a fluorescence microscope.
Capsule Staining
Certain bacteria and yeasts have a protective outer structure called a capsule. Since the presence of a capsule is directly related to a microbe’s virulence (its ability to cause disease), the ability to determine whether cells in a sample have capsules is an important diagnostic tool. Capsules do not absorb most basic dyes; therefore, a negative staining technique (staining around the cells) is typically used for capsule staining. The dye stains the background but does not penetrate the capsules, which appear like halos around the borders of the cell. The specimen does not need to be heat-fixed prior to negative staining.
One common negative staining technique for identifying encapsulated yeast and bacteria is to add a few drops of India ink or nigrosin to a specimen. Other capsular stains can also be used to negatively stain encapsulated cells (Figure \(\PageIndex{7}\)). Alternatively, positive and negative staining techniques can be combined to visualize capsules: The positive stain colors the body of the cell, and the negative stain colors the background but not the capsule, leaving halo around each cell.
Exercise \(\PageIndex{6}\)
How does negative staining help us visualize capsules?
Endospore Staining
Endospores are structures produced within certain bacterial cells that allow them to survive harsh conditions. Gram staining alone cannot be used to visualize endospores, which appear clear when Gram-stained cells are viewed. Endospore staining uses two stains to differentiate endospores from the rest of the cell. The Schaeffer-Fulton method (the most commonly used endospore-staining technique) uses heat to push the primary stain (malachite green) into the endospore. Washing with water decolorizes the cell, but the endospore retains the green stain. The cell is then counterstained pink with safranin. The resulting image reveals the shape and location of endospores, if they are present. The green endospores will appear either within the pink vegetative cells or as separate from the pink cells altogether. If no endospores are present, then only the pink vegetative cells will be visible (Figure \(\PageIndex{8}\)).
Endospore-staining techniques are important for identifying Bacillus and Clostridium , two genera of endospore-producing bacteria that contain clinically significant species. Among others, B. anthracis (which causes anthrax) has been of particular interest because of concern that its spores could be used as a bioterrorism agent. C. difficile is a particularly important species responsible for the typically hospital-acquired infection known as “C. diff.”
Exercise \(\PageIndex{7}\)
Is endospore staining an example of positive, negative, or differential staining?
Flagella Staining
Flagella (singular: flagellum) are tail-like cellular structures used for locomotion by some bacteria, archaea, and eukaryotes. Because they are so thin, prokaryote flagella typically cannot be seen under a light microscope without a specialized flagella staining technique. Flagella staining thickens the flagella by first applying mordant (generally tannic acid, but sometimes potassium alum), which coats the flagella; then the specimen is stained with pararosaniline (most commonly) or basic fuchsin (Figure \(\PageIndex{9}\)).
Though flagella staining is uncommon in clinical settings, the technique is commonly used by microbiologists, since the location and number of flagella can be useful in classifying and identifying bacteria in a sample. When using this technique, it is important to handle the specimen with great care; flagella are delicate structures that can easily be damaged or pulled off, compromising attempts to accurately locate and count the number of flagella.
Exercise \(\PageIndex{8}\)
Is the flagella stain showing the true size of the flagella?
Preparing Specimens for Electron Microscopy
Samples to be analyzed using a TEM must have very thin sections. But cells are too soft to cut thinly, even with diamond knives. To cut cells without damage, the cells must be embedded in plastic resin and then dehydrated through a series of soaks in ethanol solutions (50%, 60%, 70%, and so on). The ethanol replaces the water in the cells, and the resin dissolves in ethanol and enters the cell, where it solidifies. Next, thin sections are cut using a specialized device called an ultramicrotome (Figure \(\PageIndex{12}\)). Finally, samples are fixed to fine copper wire or carbon-fiber grids and stained—not with colored dyes, but with substances like uranyl acetate or osmium tetroxide, which contain electron-dense heavy metal atoms.
When samples are prepared for viewing using an SEM, they must also be dehydrated using an ethanol series. However, they must be even drier than is necessary for a TEM. Critical point drying with inert liquid carbon dioxide under pressure is used to displace the water from the specimen. After drying, the specimens are sputter-coated with metal by knocking atoms off of a palladium target, with energetic particles. Sputter-coating prevents specimens from becoming charged by the SEM’s electron beam.
Exercise \(\PageIndex{9}\)
- Why is it important to dehydrate cells before examining them under an electron microscope?
- Name the device that is used to create thin sections of specimens for electron microscopy.
Using Microscopy to Diagnose Syphilis
The causative agent of syphilis is Treponema pallidum , a flexible, spiral cell (spirochete) that can be very thin (<0.15 μm) and match the refractive index of the medium, making it difficult to view using brightfield microscopy. Additionally, this species has not been successfully cultured in the laboratory on an artificial medium; therefore, diagnosis depends upon successful identification using microscopic techniques and serology (analysis of body fluids, often looking for antibodies to a pathogen).  However, other approaches can also be used. For example, the cells can be thickened with silver particles (in tissue sections) and observed using a light microscope. It is also possible to use fluorescence or electron microscopy to view Treponema (Figure \(\PageIndex{13}\)).
In clinical settings, indirect immunofluorescence is often used to identify Treponema. A primary, unstained antibody attaches directly to the pathogen surface, and secondary antibodies “tagged” with a fluorescent stain attach to the primary antibody. Multiple secondary antibodies can attach to each primary antibody, amplifying the amount of stain attached to each Treponema cell, making them easier to spot (Figure \(\PageIndex{14}\)).
Preparation and Staining for Other Microscopes
Samples for fluorescence and confocal microscopy are prepared similarly to samples for light microscopy, except that the dyes are fluorochromes. Stains are often diluted in liquid before applying to the slide. Some dyes attach to an antibody to stain specific proteins on specific types of cells (immunofluorescence); others may attach to DNA molecules in a process called fluorescence in situ hybridization (FISH), causing cells to be stained based on whether they have a specific DNA sequence. Sample preparation for two-photon microscopy is similar to fluorescence microscopy, except for the use of infrared dyes.
Exercise \(\PageIndex{10}\)
What is the main difference between preparing a sample for fluorescence microscopy versus light microscopy?
Cornell University’s Case Studies in Microscopy offers a series of clinical problems based on real-life events. Each case study walks you through a clinical problem using appropriate techniques in microscopy at each step.
Microscopy and Antibiotic Resistance
As the use of antibiotics has proliferated in medicine, as well as agriculture, microbes have evolved to become more resistant. Strains of bacteria such as methicillin-resistant S. aureus (MRSA), which has developed a high level of resistance to many antibiotics, are an increasingly worrying problem, so much so that research is underway to develop new and more diversified antibiotics.
Fluorescence microscopy can be useful in testing the effectiveness of new antibiotics against resistant strains like MRSA. In a test of one new antibiotic derived from a marine bacterium, MC21-A (bromophene), researchers used the fluorescent dye SYTOX Green to stain samples of MRSA. SYTOX Green is often used to distinguish dead cells from living cells, with fluorescence microscopy. Live cells will not absorb the dye, but cells killed by an antibiotic will absorb the dye, since the antibiotic has damaged the bacterial cell membrane. In this particular case, MRSA bacteria that had been exposed to MC21-A did, indeed, appear green under the fluorescence microscope, leading researchers to conclude that it is an effective antibiotic against MRSA.
Of course, some argue that developing new antibiotics will only lead to even more antibiotic-resistant microbes, so-called superbugs that could spawn epidemics before new treatments can be developed. For this reason, many health professionals are beginning to exercise more discretion in prescribing antibiotics. Whereas antibiotics were once routinely prescribed for common illnesses without a definite diagnosis, doctors and hospitals are much more likely to conduct additional testing to determine whether an antibiotic is necessary and appropriate before prescribing.
A sick patient might reasonably object to this stingy approach to prescribing antibiotics. To the patient who simply wants to feel better as quickly as possible, the potential benefits of taking an antibiotic may seem to outweigh any immediate health risks that might occur if the antibiotic is ineffective. But at what point do the risks of widespread antibiotic use supersede the desire to use them in individual cases?
Description of Cells Under the Microscope
Once you have stained the cells, the next step is to use the microscope to describe them. You will always look for cell shape, the grouping and the color(s) that appear. These descriptions of cell morphology (shape and structure) are your microscopic observations. This is most commonly done with prokaryotes and the following tables contain proper names for shapes and groupings you should use.
Figure \(\PageIndex{15}\): (credit “Coccus” micrograph: modification of work by Janice Haney Carr, Centers for Disease Control and Prevention; credit “Coccobacillus” micrograph: modification of work by Janice Carr, Centers for Disease Control and Prevention; credit “Spirochete” micrograph: modification of work by Centers for Disease Control and Prevention)
Eukaryotic cells display a wide variety of different cell morphologies. Possible shapes include spheroid, ovoid, cuboidal, cylindrical, flat, lenticular, fusiform, discoidal, crescent, ring stellate, and polygonal (Figure \(\PageIndex{17}\)). Some eukaryotic cells are irregular in shape, and some are capable of changing shape. The shape of a particular type of eukaryotic cell may be influenced by factors such as its primary function, the organization of its cytoskeleton, the viscosity of its cytoplasm, the rigidity of its cell membrane or cell wall (if it has one), and the physical pressure exerted on it by the surrounding environment and/or adjoining cells.
Exercise \(\PageIndex{11}\)
- What are the proper names for the common shapes of bacterial cells?
- What are the proper names for the common groupings of bacterial cells?
- Why do eukaryote cells not always follow the same shapes and groupings as bacterial cells?
Key Concepts and Summary
- Samples must be properly prepared for microscopy. This may involve staining , fixation , and/or cutting thin sections .
- A variety of staining techniques can be used with light microscopy, including Gram staining, acid-fast staining , capsule staining , endospore staining, and flagella staining .
- Samples for TEM require very thin sections, whereas samples for SEM require sputter-coating.
- Preparation for fluorescence microscopy is similar to that for light microscopy, except that fluorochromes are used.
- Cells have several things unique about them when being viewed under the microscope. When recording observations, make sure to describe cell shape, grouping and color(s).
Contributor
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Nina Parker, (Shenandoah University), Mark Schneegurt (Wichita State University), Anh-Hue Thi Tu (Georgia Southwestern State University), Philip Lister (Central New Mexico Community College), and Brian M. Forster (Saint Joseph’s University) with many contributing authors. Original content via Openstax (CC BY 4.0; Access for free at https://openstax.org/books/microbiology/pages/1-introduction )


7.3: Selective Enforcement
Law enforcement officers are given enormous discretion to choose which laws to enforce and when. While discretion enables them to decide when and what to investigate, issues arise when an officer’s decision may be questionable. Officers often refer to the “ways and means act” to explain selective enforcement that results in “legally” punishing poor behaviour in a way that may not be justified. An example is best used to illustrate this line of thinking.
A police officer who is accosted by a rude and obnoxious citizen may find an obsolete charge with which to charge the person to teach him or her a lesson. The charge is usually something minor, such as riding a bicycle without a bell. While technically the bylaw may require riders to have a bicycle bell, it may very rarely be used. In addition, the police officer may not have enforced this bylaw in the past and is aware that numerous people ride bicycles without bells.
While the officer has a legal right to charge the citizen, he or she should reflect on how this case will look if it is taken to court. The officer’s credibility will be questioned after the circumstances of the case are read in court. Typically, the citizen’s obnoxious behaviour, when recalled later on, will pale in comparison to what the court could rule as an abuse of authority by the police officer. Officers must be objective and treat everyone equally, regardless of the behaviour exhibited. When confronted with obnoxious citizens, officers must strive to remain unmoved, unnerved, and calm. Using discretion as a tool to charge a citizen with obsolete laws and bylaws should be avoided for the good of the officer, the agency, and society.


4.0: Introduction
Sara, an 18-year-old mother, brings her infant, Jasper, to the rural health clinic for his 2-month checkup. Nurse Mateo notes that Jasper is due to receive several vaccinations. He begins explaining their purpose to Sara and gives her an immunization schedule for a child’s first year. Sara frowns and seems reluctant to take the schedule; she says, “Jasper has already had lots of shots,” and she wonders about how well vaccinations even work since her father “still got COVID-19 even though he was boosted.” Mateo, understanding this is an opportunity to educate the new parent on illness prevention, begins describing the different childhood diseases that are now preventable by immunizations. Using parent-friendly handouts from the Centers for Disease Control and Prevention (CDC), he discusses issues that may occur when an unimmunized child attends day care or school or socializes with other children, along with the possible consequences of not receiving the recommended vaccinations. No longer frowning, Sara nods and follows along as Mateo points out the different vaccinations on the handout.
Clinic visits like this one are opportunities for clients to obtain information on keeping themselves and their families healthy and free from illness. Providing education on preventive care is one example of how nurses work in the community. Nurses like Mateo must understand the health needs of their communities to enhance health. This chapter explores the health needs of a population by defining health, describing the current health status of the U.S. population, and discussing methods used to measure it. The chapter also explores the nurse’s role in creating a culture of health by promoting actions through which good health and well-being can be achieved across geographic, demographic, and social sectors.