Muscle Physiology: Contraction

Question 1

What is another name for the neuromuscular junction?

Answer 1

Motor end plate

Question 2

Each muscle fiber has how many motor end plates?

Answer 2

1, approximately midway along its length

Question 3

What is the sequence of events that happen at the neuromuscular junction?

Answer 3

1. Action potential arrives at the axon terminal of the somatic motor neuron
2. This triggers the opening of Ca2+ channels and Ca2+ is released into the axon terminal, moving down its electrochemical gradient
3. Ca2+ entry causes ACh to be released by exocytosis
4. ACh diffuses across the synaptic cleft and binds to receptors on the sarcolemma
5. ACh binding opens ion channels in the receptors that allow simultaneous passage of Na+ into the muscle fiber and K+ out. More enter than exit, which produces a change in membrane potential called the end plate potential
6. ACh effects are terminated by its breakdown in the synaptic cleft by acetylecholinesterase. It diffuses away from the junction.

Question 4

What are the nerve cells that activate skeletal muscle fibers called?

Answer 4

Somatic motor neurons