Characteristics of whole muscle contraction
Several hundreds to several thousands nerve fibers enter most muscles. On an average, a single motor nerve fiber can innervate about 180 muscle fibers. Thus, stimulating one nerve fiber, can cause contraction of 180 muscle fibers all at the same time. All the muscle fibers innervated by the same nerve fiber is called a motor unit because they are always excited simultaneously and contract together.
In the human body, muscle contraction is of both isometric and isotonic types.
When a person is simply standing, he tenses his leg muscles to maintain a fixed position of the joints. This is isometric contraction.Isometric means 'same length'. Here the muscle tightens but does not shorten. When a person is walking and moving his legs, or when he is lifting his arms, the contraction is isotonic contraction. Isotonic means 'same force'. Here the muscle shortens in length.
A single muscle is made up of thousands of individual muscle fibers. Every fiber extends the entire length of the muscle and is attached at each end to muscle tendons. When stimulated, muscle fibers contract, and the force of contraction is transmitted to the bones through the tendons.