Name: Muscular System  
Definition: The muscular system is comprised mostly of skeletal muscles attached to bones, but also includes cardiac and smooth muscles.
Structure: The skeletal muscles are attached to the bones at places called orgins, in locations that provide movements of the bones upon voluntary muscular contraction. Cardiac muscle makes up the heart, and smooth muscle is in many places, especially in the digestive and the circulatory systems. Muscles are stimulated by nerve impulses that travel by creating action potentials that reach the end of a nerve fiber.


Function: The skeletal muscles respond to the will, and are the engines that maintain posture and produce motion. Cardiac and smooth muscles are controlled by the autonomic nervous system. As action potentials either reach the end of a nerve, the either stimulate another action potential in another fiber, or the reach an effector cell, where they stimulate the release of neurotransmitters. If for example, the effector cell is at a myo-neural endplate, a muscle contraction will result, if the signal is strong enough, or reaches a certain threshold.


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