Skeletal Muscle Contraction
Steps – Excitation
1. An action potential at the axon terminal of a motor neuron triggers the release of the
neurotransmitter acetylcholine.
2. Acetylcholine diffuses across the synaptic cleft and binds to receptors on the motor end
plate of a skeletal muscle fiber.
3. Na+ channels open, causing Na+ to enter the sarcolemma and depolarize it.
4. Depolarization triggers an action potential which travels through the sarcolemma, down
the T-tubules, and finally reaches the sarcoplasmic reticulum.
5. Depolarization of the sarcoplasmic reticulum results in the release of calcium ions
into the sarcomere.
Steps – Contraction
1. Calcium ions combine with troponin, causing a conformational change.
2. Troponin now moves pulling tropomyosin away from the binding sites on actin.
3. ATP attaches to myosin heads, which can then bind to actin forming a cross-bridge.
