Muscle contraction: Excitation-Contraction Coupling

Author: Scott A. Sheffield MS

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In skeletal muscle fibers, electrochemical activity triggers myofilament movement. These linked events are referred to as excitation-contraction coupling.

An illustration showing the spinal cord, a spinal nerve, an axon of a motor neuron connecting to skeletal muscle fibers through a neuromuscular junction

The excitation process begins when the image descriptionacetylcholine (ACh) is released by a motor neuron at the neuromuscular junction.

A nerve coming from the spinal cord innervates a muscle fiber via its motor neuron axon. The neuromuscular junction is magnified.
A nerve coming from the spinal cord innervates a muscle fiber via its motor neuron axon. The neuromuscular junction is magnified.
A nerve coming from the spinal cord innervates a muscle fiber via its motor neuron axon. The neuromuscular junction is magnified.
A nerve coming from the spinal cord innervates a muscle fiber via its motor neuron axon. The neuromuscular junction is magnified.
A nerve coming from the spinal cord innervates a muscle fiber via its motor neuron axon. The neuromuscular junction is magnified.
A nerve coming from the spinal cord innervates a muscle fiber via its motor neuron axon. The neuromuscular junction is magnified.
A nerve coming from the spinal cord innervates a muscle fiber via its motor neuron axon. The neuromuscular junction is magnified.
A nerve coming from the spinal cord innervates a muscle fiber via its motor neuron axon. The neuromuscular junction is magnified.
A nerve coming from the spinal cord innervates a muscle fiber via its motor neuron axon.
Acetylcholine (ACh) release

Stimulation of the muscle fiber by the ACh neurotransmitter generates waves of  image descriptionaction potentials (impulses) that spread out across the sarcolemma.

The action potentials enter the muscle fiber from the sarcolemma and cause calcium ions (= Ca2+) to be released from the sarcoplasmic reticulum. A rise in cytoplasmic calcium initiates the image descriptioncontraction process.

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Contraction Physiology