Neuromuscular Junction

Question 1

What makes up the neuromuscular junction?

Answer 1

Presynaptic knob = motor neurone
Post synaptic membrane = sarcolemma

Question 2

Describe how synaptic transmission across the neuromuscular junction results in muscle contraction.

Answer 2

1. Action potential arrives at the pre synaptic knob which stimulates calcium ion channels to open and calcium ions diffuse into the knob
2. This causes vesicles containing acetylcholine to fuse with the presynaptic membrane and release the acetylcholine into the synaptic cleft
3. Acetylcholine diffuses across the synaptic cleft and binds to complementary receptor proteins on the post synaptic membrane (sarcolemma)
4. This stimulates Na+ channels to open and Na+ diffuses into the post synaptic knob causing depolarisation
5. If the threshold is passed, action potentials will occur in the sarcolemma and will move along the muscle membrane folds deep within the muscle
6. This stimulates calcium ions to diffuse out of the sarcoplasmic reticulum which cause muscle contraction