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.
Muscular system. The muscular system is an organ system consisting of skeletal, smooth and cardiac muscles. It permits movement of the body, maintains posture, and circulates blood throughout the body. The muscular system in vertebrates is controlled through the nervous system, although some muscles (such as the cardiac muscle) can be completely autonomous.