AP - Neuromuscular Junctions & Action Potentials

Question 1

what is the neuromuscular junction?

Answer 1

a synaptic connection between the terminal end of a motor nerve and a muscle (motor end plate)

Question 2

what neurotransmitter is important for the neuromusclar junction?

Answer 2

Acetylcholine

Question 3

explain the physiology of the neuromuscular junction

Answer 3

1. nerve impulse coming down to teh terminal motor nerve
2. triggers the influx of Ca2+ from voltage gated channels
3. results in vesicle migration to the nerve terminal membrane (vesicles contain acetylcholine) and release of acetylcholine into the synaptic cleft
4. acetylcholine binds to nicotinic ACh receptors on postsynaptic cell (muscle cell)
5. results in the opening of ligand-gated channels ➔ influx of Na2+
6. action potential gets propagated through the muscle cell
7. acetylcholine gets degraded by acetylcholinesterase in the synaptic cleft

Question 4

components of the neuron

Answer 4

dendrites: receive information from neighbouring axons/neurons

cell body: maintains neuron heath/function

axons: carry out electrical impulses to communicate with neighbouring cells

Schwann cells of myelin sheaths: to help with axon insulation and promote quicker AP propagation

nodes of Ranvier: the spaces inbetween the myelin sheaths where there are gates and depolarization

Question 5

explain the charge changes and depolarization of an action potential

Answer 5

1. stimulus resulting in local charge change from the resting membrane potential (~ -65 mV)
2. if the local charge meets the threshold potential ➔ all or nothing, the cell depolarizes
3. voltage gated Na channels open ➔ charge in the cell becomes positive
4. triggers the opening of nearby voltage gated Na channels ➔ influx of Na
5. repolarization: Na gates are inactivated and K voltage gated channels open allowing some of the + change to leave the cell + Na/K pump is working to restore the resting membrane potential
6. absolute refractory period - Na channels are inactivated and cannot receive a new stimuli
7. slight hyperpolairzation because of the K channels taking too much + out of the cell

• can also be stimulated via Na+ influx from ligand gated channels w/ neurotransmitters - acetylcholine

Question 6

how is an action potential propagated?

Answer 6

the depoalrization opens the Na gates in proximity and the inactivation of the Na gates results in the charges (+) only moving in one direction

the myelin sheaths allow for quicker conduction as there are no channels and so + can be bumped forward into areas where there are channels ➔ saltatory conduction