Question

choose the answer that places the following key steps of skeletal muscle contraction into their appropriate order:

1. acetylcholine binds receptor.
2. acetylcholine is released from neuron.
3. calcium ions released by sarcoplasmic reticulum.
4. sarcolemma action potential is propagated.
5. sodium enters the muscle cell.

a 2; 1; 5; 4; 3
b 1; 2; 3; 4; 5
c 2; 1; 3; 4; 5
d 1; 2; 5; 4; 3

Explanation:

• First, acetylcholine is released from the neuron (step 2).
• Then, it binds to the receptor (step 1).
• After that, sodium enters the muscle cell (step 5).
• Next, the sarcolemma action potential is propagated (step 4).
• Finally, calcium ions are released by the sarcoplasmic reticulum (step 3).

Answer:

A. 2; 1; 5; 4; 3