Neuromuscular Junction Questions

What is an action potential? What charge is it?

When the charge of the membrane rapid raises, then falls. Positive charged.

What is a resting potential? What charge is it?

Typically state of a cell. Negative charge.

What is the neuron’s main function?

Action potential travels down it to muscle. Tells muscle to contract.

How does the Ca2+ channel open and close?

Normally closed. Activated when depolarized (charge becomes positive because of action potential)

What are the synaptic vesicles? What do they have to do with Ca2+?

Like a bubble that can store neurotransmitters and release the into the synapse.

What is acetylcholine?

Neurotransmitter. Found at neuromuscular (nerve to skeletal muscle) junctions.

What role does Na+ play in the Neuromuscular Junction?

Depolarize the muscle membrane and create an action potential in the muscle cell.

How does the ligand-gated Na+ channel open and close?

It opens when ACh binds to it. It closes when ACh unbinds.

What does acetylcholinesterase do?

An enzyme that removes ACh from synaptic cleft by splitting it into acetic acid and choline.

1. An action potential arrives at the presynaptic terminal and

causes voltage gated Ca2+ channels to open

2. Calcium ions enter the presynaptic terminal and

initiate the release of the neurotransmitter acetylcholine (ACh) from synaptic vesicles.

3. ACh is released into the synaptic cleft and

binds to the ligand-gated Na+ channels on the postsynaptic membrane

4. Ligand-gated Na+ channels open and Na+ enters the postsynaptic cell, causing

the membrane to depolarize

4. 4.5 If depolarization passes the threshold (if enough Na+ comes in),

an action potential is generated along the postsynaptic membrane.

5. ACh unbinds from the ligand-gated Na+ channel and

the channels close

6. The enzyme acetylcholinesterase removes acetylcholine from the synaptic cleft by

breaking it down into acetic acid and choline

7. Choline is symported into the presynaptic terminal to be

recycled into ACh.

7. 7.5 Acetic acid diffuses away from

the synaptic cleft

8. ACh is reformed within the presynaptic terminal using

acetic acid (generated from metabolism) and from choline recycled from the synaptic cleft.

8. 8.5 ACh is then taken up by

synaptic vesicles