10 Steps of Muscle Contraction
This flashcard set outlines the step-by-step process of how a nerve impulse initiates muscle contraction at the neuromuscular junction. It explains how signals travel from neurons to muscle fibers, triggering the physiological events that lead to muscle activation.
Step 1 - Nerve Impulse reaches Neuromuscular Junction
Nerve signal from brain arrives at neuromuscular junction & axon terminal of motor neuron

Key Terms
Step 1 - Nerve Impulse reaches Neuromuscular Junction
Nerve signal from brain arrives at neuromuscular junction & axon terminal of motor neuron
Step 2 - Acetylcholine (ACH) Released by Motor Neuron
Motor neuron releases neurotransmitter Acetylcholine (Ach) into synaptic gap between nerve & muscle cells
Step 3 - ACH binds to Muscle Receptor Sites
ACH (key) binds to receptors on the muscle cell
Step 4 - Sodium Channels in muscle OPEN
Receptors stimulated by ACH allow sodium (Na+) channels in muscle cell to open
Step 5 - Na+ Ion rush causes change in cell charge
Na+ influx into muscle cell causes polarity change, creates electrical current called an Action Potential
Step 6 - Action Potential charge travels down muscle cell
Action Potential impulse travels down the sarcolemma membrane and all over the muscle cell
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| Term | Definition |
|---|---|
Step 1 - Nerve Impulse reaches Neuromuscular Junction | Nerve signal from brain arrives at neuromuscular junction & axon terminal of motor neuron |
Step 2 - Acetylcholine (ACH) Released by Motor Neuron | Motor neuron releases neurotransmitter Acetylcholine (Ach) into synaptic gap between nerve & muscle cells |
Step 3 - ACH binds to Muscle Receptor Sites | ACH (key) binds to receptors on the muscle cell |
Step 4 - Sodium Channels in muscle OPEN | Receptors stimulated by ACH allow sodium (Na+) channels in muscle cell to open |
Step 5 - Na+ Ion rush causes change in cell charge | Na+ influx into muscle cell causes polarity change, creates electrical current called an Action Potential |
Step 6 - Action Potential charge travels down muscle cell | Action Potential impulse travels down the sarcolemma membrane and all over the muscle cell |
Step 7 - Release of Ca+ into cell | Action potenial impulse causes the sarcoplasmic reticulum web to release stored Ca++ into the cell and around sarcomere contraction units |
Step 8 - Ca+ influx causes Myosin & Actin to bind | Inside sarcomeres, Ca++ ions allow myosin heads to fit onto actin filaments |
Step 9- CONTRACTION | Myosin heads "pull" Actin filaments toward center, allowing filaments to slide past each other in opposite directions, shortens sacromere |
Step 10 - RELAXATION | When action potential ends, Ca++ is reabsorbed by sacroplasmic reticulum, myosin & actin return to orginal position, and muscle relaxes |