Unit 16 Muscle physiology

Question 1

Explain Neuromuscular Junction

Answer 1

• an action potential arrives at the axon terminal of a motor neuron
• this triggers voltage gated Ca2+ channels in the membrane of the somatic and bulb of the axon terminal to open, allowing Ca2+ to diffuse into the cytosol of the synaptic end bulb
• influx of Ca2+ causes synaptic vesicles in the neuron to fuse with its plasma membrane, releasing a contents by exocytosis into the space between a neuron and the muscle fibre – the synaptic cleft
• ACh diffuses across from the synaptic cleft and binds to receptors located on proteins and embedded in the sarcolemma
• ACh binding causes a ligand – gated ion channel in the proteins to open
• positively charged ions diffuse into the sarcoplasm causing depolarization
• voltage-gated Na+ channels opens, Na+ now diffuse into the sarcoplasm
• this causes a rapid spread of action potential along the entire sarcolemma

Question 2

How does calcium ions get into the sarcoplasm?

Answer 2

1. Muscle action potential travels along sarcolemma
2. Muscle action potential travels across T-tubules
3. Muscle action potential causes voltage-sensitive proteins in the T – tubule membranes to change shape
4. The shape change of these proteins pull on calcium ion channels proteins in the SR, opening them
5. Calcium ions then diffuse out of the SR into the sarcoplasm