Neuromuscular Junction

What happens at the Neuromuscular Junction (NMJ)?

1. action potential in motor neuron – induces release of acetylcholine into neuromuscular junction.
2. muscle cell is depolarized, creating an end plate potential (EPP)
3. opening of Na+ voltage gated channels causes a muscular action potential.
4. this causes voltage-gated $Ca^{ 2+}$ channels in sarcoplasmic reticulum to release $Ca^{ 2+}$ into cytosol which bind troponin and pull off tropomyosin
5. $Ca^ {2+}$ pumped back into sarcoplasmic reticulum after muscle contraction

1 Motor neuron AP will ALWAYS cause at least 1 AP on the muscle cell

Excitation Coupling

• This is the relationship between excitation of a muscle and the actual contraction itself.
• The connection between the two is done using Ca+ ions
• Important terms to know:
• Sarcoplasmic Reticulum: an organ that covers the myofibril like a sock. It reacts to voltage changes in the T-tubules.
• T-tubule: a ring that goes around the myofibril. This is where the AP can propagate.