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 body has three types of muscles: smooth, skeletal and cardiac. The muscular system controls smiling. Skeletal muscles are linked to the bones in the skeleton with the help of tendons. Most of a person's internal organs are lined with smooth muscle. An illustration of the human muscular system.