Hole's Human Anatomy & Physiology (Shier), 12th Edition

Chapter 9: Muscular System

Action Potentials and Muscle Contraction

How do nerve impulses cause muscle contraction? Skeletal muscle is under voluntary control. Nerve impulses that originate in the central nervous system cause muscles to contract. Both neurons and muscle tissue conduct electrical current by moving ions across cellular membranes. A motor neuron ends in a synapse with a muscle fiber. The neuron releases acetylcholine and transfers the action potential to the muscle tissue. The signal will travel through the tissue and trigger the contraction of individual sarcomeres. One synapse generally controls an entire muscle fiber. One motor neuron usually controls several adjacent muscle fibers. A group of fibers under the control of a single motor neuron is known as a motor unit.

View the animation below, then complete the quiz to test your knowledge of the concept.


An action potential spreads or is propagated through a muscle fiber...
A)by the myosin myofilament.
B)by the T-tubules.
C)by the crossbridge
D)by the sarcoplasmic reticulum.
E)by the actin myofilament.

What structures do the calcium ions bind to when muscle contraction is initiated?
A)the actin myofilament.
B)the troponin molecule.
C)the tropomyosin molecule.
D)the sarcoplasmic reticulum.
E)the sarcolemma.

Cross bridges form between...
A)troponin and tropomyosin.
B)calcium and sodium.
C)the sarcolemma and the sarcoplasmic reticulum.
D)the T-tubules and the sarcolemma.
E)the actin filaments and the myosin heads.

An action potential introduced at the neuromuscular junction is propagated along the sarcoplasmic reticulum.

In response to an action potential depolarizing the muscle fiber, calcium ions diffuse from the sarcolemma into the sarcoplasm.
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