1 Voltage can be thought of as the driving force (although it is not really a force.) behind current. 2  Things like batteries are voltage sources. 3  The voltage across the terminals of a battery tends to stay pretty constant. 4  When you connect a device across the battery terminals a current flows through the device.
Three types of muscles. The muscular system can be broken down into three types of muscles: skeletal, smooth and cardiac, according to the NIH. Skeletal muscles are the only voluntary muscle tissue in the human body and control every action that a person consciously performs. Most skeletal muscles are attached to two bones across a joint, so the muscle serves to move parts of those bones closer to each other, according to The Merck Manual.
The muscular system. The muscular system is composed of specialized cells called muscle fibers. Their predominant function is contractibility. Muscles, attached to bones or internal organs and blood vessels, are responsible for movement. Nearly all movement in the body is the result of muscle contraction. Exceptions to this are the action of cilia, the flagellum on sperm cells, and amoeboid movement of some white blood cells. The muscular system in vertebrates consists of three different types of muscles: cardiac, skeletal and smooth.