Discuss excitation-contraction coupling.
- - sequence of events whereby an action potential (electrical signal) in the sarcolemma causes contraction
- - dependent on *neural input* from motor neuron
- - requires *calcium release* from the sarcoplasmic reticulum
(1) Acetylcholine is released from a motor neuron and binds to receptors, triggering an action potential that is propagated along the sarcolemma and down the T-tubulues
(2) Voltage-sensitive tubule proteins respond to AP and change shape, opening Ca2+ release channels in the sarcoplasmic reticulum. Massive amounts of Ca2+ flow into the cytosol within a millisecond.
(3) Calcium binds to troponin, causing it to change shape, remove blocking action of tropomyosin, and expose myosin binding sites.
(4) Myosin binds to actin, forming cross bridges and crossbridge cycling begins.
Ca2+ levels drop immediately afterwards.