The Muscular System

The muscular system is the anatomical system of a species that allows it to move. The muscular system in vertebrates is controlled through the nervous system, although some muscles can be completely autonomous (Wikipedia, 2010). There are three different types of muscles: skeletal, cardiac, and smooth muscles. Skeletal muscles are connected at either or both ends to a bone so move parts of the skeleton. They are also called striated muscles because they have a series of striped or striated, thread-like myofibrils. They can also be controlled voluntarily.

Cardiac muscles include the muscles of the heart. They move involuntarily, meaning that they are incapable of being moved by conscious thought. They are controlled by the sinus node influenced by the autonomic nervous system. Smooth muscles are controlled directly also by the autonomic nervous system and are involuntary. They include muscles of the viscera, like the walls of blood vessels, intestines, and other hollow structures and organs in the body. As stated above, skeletal muscles move voluntarily. They need to be stimulated by the nervous system.

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They are excitable and are subject to depolarization by the neurotransmitter acetylcholine (ACH), released at the neuromuscular junction by motor neurons, then binds to the receptor sites. Stimulation of the receptor sites causes an electrical impulse to form in the muscle membrane. The electrical impulse travels along the muscle membrane and penetrates deep into the muscle and stimulates the sarcoplasmic reticulum to release calcium into the sarcomere (a contractile unit of a mofibril) area. Calcium allows the actin, myosin, and ATP to interact, causing cross-bridge formation and muscle contraction.

This process continues as long as calcium is available to the actin and myosin. Muscle relaxation occurs when calcium is pumped back into the sarcoplasmic reticulum, away from the actin and myosin. When calcium moves in this way, the actin and myosin cannot interact, and the muscle relaxes. (Contraction and Relaxation, 2005). References: Contraction and Relaxation (2005). Retrieved May 7, 2010, from http://www. innvista. com/ health/anatomy/contract. htm Muscle contraction (2010). Retrieved May 7, 2010 from http://en. wikipedia. org/wiki/ Muscular_system

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