Question

which of the following steps of exciting a muscle occurs immediately before the electrochemical signal spreads along the sarcolemma to the transverse tubules? a.) acetylcholine (ach) release from the axon terminal b.) acetylcholine (ach) diffusion across the synaptic cleft c.) calcium release from the sarcoplasmic reticulum d.) depolarization of the muscle fiber

Explanation:

When a nerve impulse reaches the axon terminal, acetylcholine (ACh) is released (a). Then ACh diffuses across the synaptic cleft (b). After binding to receptors on the muscle fiber membrane, it causes depolarization of the muscle fiber (d). Depolarization is the step that immediately precedes the spread of the electrochemical signal along the sarcolemma to the transverse tubules. Calcium release from the sarcoplasmic reticulum (c) occurs later in the muscle - contraction process, after the signal has reached the transverse tubules and triggered calcium release.

Answer:

d. Depolarization of the muscle fiber