head and neck anatomy head and neck anatomy this article describes the anatomy of the head and neck of the human body, including the brain, bones, muscles, blood vessels, nerves, glands, nose, mouth, teeth, tongue, and throat. an mri scan of a human head. structure bones the head rests on the top part of the vertebral column, with the skull joining at c1 (the first cervical vertebra known as the atlas). the skeletal section of the head and neck forms the top part of the axial skeleton and is made up of the skull, hyoid bone, auditory ossicles, and cervical spine. the skull can be further subdivided into: the cranium (8 bones: frontal, 2-parietal, occipital, 2-temporal, sphenoid, ethmoid), and the facial bones (14 bones: 2-zygomatic, 2-maxillary, 2-palatine, 2-nasal, 2-lacrimal, vomer, 2-inferior conchae, mandible). the occipital bone joins with the atlas near the foramen magnum, a large hole (foramen) at the base of the skull. the atlas joins with the occipital condyle above and the axis below. the spinal cord passes through the foramen magnum. muscles groupnamenervefunction facial expressionepicranius: frontalis and occipitalisfacial nerveeyebrows and scalp facial expressionorbicularis orisfacial nervecloses lips facial expressionzygomaticus majorfacial nervesmiling facial expressionzygomaticus minorfacial nervesmiling facial expressionlevator labii superiorisfacial nerveupper lip facial expressionlevator labii superioris alaeque nasifacial nerveupper lip facial expressiondepressor labii inferiorisfacial nervelower lip facial expressiondepressor anguli orisfacial nervefrowning facial expressionplatysmafacial nervefrowning (during fear or shock) facial expressionbuccinatorfacial nervecheeks facial expressionmentalisfacial nervechin facial expressionplatysmafacial nervefrowning facial expressionrisoriusfacial nervemouth angle facial expressionorbicularis oculifacial nervecloses eye facial expressionnasalisfacial nerveflare nostrils facial expressioncorrugator supercillifacial nerveeyebrow facial expressionlevator palpebrae superiorisoculomotor nerveupper eyelid chewing – lower mandiblemassetertrigeminal nerveclosing and protruding mandible, chewing – lower mandibletemporalistrigeminal nerveelevates and controls side to side movement of mandible chewing – lower mandiblemedial pterygoidtrigeminal nerveelevates mandible, chewing – lower mandiblelateral pterygoidtrigeminal nerveprotracts mandible, opens mouth. tongue – extrinsicgenioglossushypoglossal nerveprotraction, tongue – extrinsicstyloglossushypoglossal nerveelevation and retraction, tongue – extrinsichyoglossushypoglossal nervedepresses tongue tongue – extrinsicpalatoglossuspharyngeal plexus, pharyngeal branch of vagus nerveelevates tongue while swallowing oral cavity floordigastrictrigeminal nerve and facial nervehyoid and mandible movement oral cavity floorstylohyoidfacial nerveelevates hyoid oral cavity floormylohyoidtrigeminal nervehyoid and mandible movement oral cavity floorgeniohyoidcervical nerve c-1hyoid, tongue, and mandible movement move headsternocleidomastoidaccessory nervenodding and turning move headsemispinalisdorsal rami of cervical nervesextends head, supports turning move headsplenius capitisdorsal rami of middle and lower cervical nervesextend head, supports turning move headlongissimus capitisdorsal rami of middle and lower cervical nervesextends head, supports turning move headrectus capitis posterior majorsuboccipital nerve c-1extends head move headrectus capitis posterior minorsuboccipital nerve c-1extends head skin the head and neck is covered in skin and its appendages, termed the integumentary system. these include hair, sweat glands, sebaceous glands, and sensory nerves. the skin is made up of three microscopic layers: epidermis, dermis, and hypodermis. the epidermis is composed of stratified squamous epithelium and is divided into the following five sublayers or strata, listed in order from outer to inner: stratum corneum, stratum lucidum, stratum granulosum, stratum spinosum, stratum germinativum also called stratum basale. the deepest layer is the miotic layer, stratum basale producing daughter cells by mitosis. mouth main article: human mouth the mouth, also called the oral cavity, is the entranceway into the digestive system containing both primary and accessory organs of digestion. teeth main article: human tooth two rows of teeth are supported by facial bones of the skull, the maxilla above and the mandible below. adults have 32 permanent teeth, and children have 20 deciduous teeth. there are various tooth shapes for different jobs. for example, when chewing, the upper teeth work together with the lower teeth of the same shape to bite, chew, and tear food. the names of these teeth are: (1) incisors, there are eight incisors located in the front of the mouth (four on the top and four on the bottom). they have sharp, chisel-shaped crowns that cut food. (2) cuspids (or canine tooth), the four cuspids are next to each incisor. cuspids have a pointed edge to tear food. (3) premolars (or bicuspids), the four pairs of molars are located next to the cuspids. they crush and tear food. (4) molars, there are twelve molars, in sets of three, at the back of the mouth. they have wide surfaces that help to grind food. the white visible part of a tooth is called the crown. the rounded upper projections of the back teeth are cusps. the hard white exterior covering of the tooth is the enamel. as the tooth tapers below the gumline, the neck is formed. below the neck, holding the tooth into the bone, is the root of the tooth. the inner portions of the tooth consist of the dentin, a bonelike tissue, and the pulp. the pulp is a soft tissue area containing the nerve and blood vessels to nourish and protect the tooth, located within the pulp cavity. a tooth sits in a specialized socket called the alveolus. the tooth is held in location by a periodontal ligament, with the assistance of cementum. teeth are surrounded by gingiva, or gums, part of the periodontium, support tissue of oral cavity protection. the periodontium includes all of the support membranes of the dental structures surround and support the teeth such as the gums and the attachment surfaces and membranes. these include epithelial tissues (epithelium), connective tissues, (ligaments and bone), muscle tissue and nervous tissue. salivary glands main article: salivary glands there are three sets of salivary glands: the parotid, the submandibular and the sublingual glands. the (exocrine) glands secrete saliva for proper mixing of food and provides enzymes to start chemical digestion. saliva helps to hold together the formed bolus which is swallowed after chewing. saliva is composed primarily of water, ions, salivary amylase, lysozymes, and trace amounts of urea. tongue the tongue is a specialized skeletal muscle that is specially adapted for the activities of speech, chewing, developing gustatory sense (taste) and swallowing. the tongue contains two sets of muscles, the intrinsic- involved with shape of tongue, and the extrinsic- involved with tongue movement. it is attached to the hyoid bone. terms meaning tongue include "glosso" (from greek) and "lingual" ((from latin). microanatomy the outer surfaces of the head and neck are lined by epithelium. the protective tissues of the oral cavity are continuous with the digestive tract are called mucosa or mucous membranes. the cells of the inner oral cavity are called the buccal mucosa. the oral cavity is lined by a stratified squamous epithelium containing about three layers of cells. they line the oral, nasal, and external auditory meatus, (ear), providing lubrication and protection against pathogens. the lips are also protected by specialized sensory cells called meissner's corpuscles. blood, lymph and nerve supply blood supply blood circulates from the upper systemic loop originating at the aortic arch, and includes: the brachiocephalic artery, left common carotid artery and left subclavian artery. the head and neck are emptied of blood by the subclavian vein and jugular vein. right side of neck dissection showing the brachiocephalic, right common carotid artery and its branches the brachiocephalic artery or trunk is the first and largest artery that branches to form the right common carotid artery and the right subclavian artery. this artery provides blood to the right upper chest, right arm, neck, and head, through a branch called right vertebral artery. the right and left vertebral artery feed into the basilar artery and upward to the posterior cerebral artery, which provides most of the brain with oxygenated blood. the posterior cerebral artery and the posterior communicating artery are within the circle of willis. the left common carotid artery divides to form the: internal carotid artery (ica) and an external carotid artery (eca). the ica supplies the brain. the eca supplies the neck and face. the left subclavian artery and the right subclavian artery, one on each side of the body form the internal thoracic artery, the vertebral artery, the thyrocervical trunk, and the costocervical trunk. the subclavian becomes the axillary artery at the lateral border of the first rib. the left subclavian artery also provides blood to the left upper chest and left arm. blood–brain barrier the blood–brain barrier (bbb) is semi-permeable membrane that controls the capillary leak potential of the circulatory system. in most parts of the body, the smallest blood vessels, called capillaries, are lined with endothelial cells, which have small spaces between each individual cell so substances can move readily between the inside and the outside of the capillary. this is not in the case of brain. in the brain, the endothelial cells fit tightly together to create a tight junction and substances cannot pass out of the bloodstream. specialized glial cells called astrocytes form a tight junction or protective barrier around brain blood vessels and may be important in the development of the bbb. astrocytes may also be responsible for transporting ions (electrolytes) from the brain to the blood. venous drainage blood from the brain and neck flows from: (1) within the cranium via the internal jugular veins, a continuation of the sigmoid sinuses. the right and left external jugular veins drain from the parotid glands, facial muscles, scalp into the subclavian veins. the right and left vertebral veins drain the vertebrae and muscles into the right subclavian vein and into the superior vena cava, into the right atrium of the heart. lymphatic system the lymphatic system drains the head and neck of excess interstitial fluid via lymph vessels or capillaries, equally into the right lymphatic duct and the thoracic duct. lymph nodes line the cervical spine and neck regions as well as along the face and jaw. the tonsils also are lymphatic tissue and help mediate the ingestion of pathogens. tonsils in humans include, from superior to inferior: nasopharyngeal tonsils (also known as adenoids), palatine tonsils, and lingual tonsils. together this set of lymphatic tissue is called the tonsillar ring or waldeyer's ring. nerve supply the spinal nerves arise from the spinal column. the top section of the spine is the cervical section, which contains nerves that innervate muscles of the head, neck and thoracic cavity, as well as transmit sensory information to the cns. the cervical spine section contains seven vertebrae, c-1 through c-7, and eight nerve pairs, c-1 through c-8. there is the formation of an extensive network of nerve groups or tracts attaching to the spinal cord in arrangements called rami or plexus. the sensory branches of spinal nerves include: lesser occipital, c-2, great auricular, (c-2 and c-3); transverse cervical, c-2 and c-3; and supraclavicular, c-3 and c-4. these nerve groups transmit afferent (sensory) information from the scalp, neck, and shoulders to the brain. the motor branches of spinal nerves include: ansa cervicalis, dividing into a superior root, c-1, and an inferior root, c-2 and c-3, and the phrenic nerve, c-3 to c-5, the segmental nerve branches, c-1 to c-5. these nerve groups transmit efferent nerve (motor) information from the brain to muscle groups of the scalp, neck, diaphragm (anatomy), and shoulders. additionally there are: (c5-c8, and t1) brachial plexus, providing the entire nerve supply of the shoulder and upper limb; and includes supraclavicular branches (dorsal scapular, suprascapular, long thoracic) lateral cord (musculocutaneous, lateral antibrachial cutaneous, lateral head of median nerve), medial cord (ulnar, medial head of median nerve, medial antibrachial cutaneous, medial brachial cutaneous), posterior cord (axillary, radial), controlling the arm. damage to a person's spinal cord above c-5 may result in respiratory arrest and death if medicinal aid does not intervene. cranial nerves twelve pairs of cranial nerves emerge from the brain; these affect movements and sensation, and some special organs such as hearing of parts of the head and neck. function movements of the neck includes: flexion, extension, (nodding yes), and rotation (shaking head no). the mouth has evolved to support chewing, (mastication) and swallowing (deglutition), and speech (phonation). in addition to the teeth, other structures that aid chewing are the lips, cheeks, tongue, hard palate, soft palate, and floor of the mouth. endocrine glands several glands of the endocrine system are found within the head and neck. endocrine means that the secretion is used within the body. endocrine glands are termed as ductless and release their secretions directly into the blood. the endocrine system is under the direct supervision of the nervous system, using the negative feedback principal of homeostasis, to create hormones which act as chemical instant messengers. the hypothalamus