One way to look at the human body is to imagine it is a robot. If you were designing a robot, you would probably fit it with a central computer, and have electrical signals sent along wires from the computer to little motors. The little motors would then operate rods, pistons and claws, which could then perform tasks such as lift objects or make movements.
In the human body the central computer is your brain, and those electrical signals are sent along nerves to the muscles…. your motors!
The muscles operate bones, such as those in the arms and hands, to make movements, lift objects and so on. Muscle tissue has five principal characteristics that enable it to carry out its functions:
Excitability: muscle cells are able to respond to stimulus
Contractility: the ability to contract, thus generating force to do work
Extensibility: muscle fibres can be stretched beyond their normal length
Elasticity: after being stretched, muscles will return to their normal length
Conductivity: the ability of a muscle cell to conduct electrical impulses