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What do neuromuscular junctions deal with?
skeletal muscle action potientials
Where is the neuromuscular junction/
at the distal end of the motor neuron, where lower motor neuron innervates a skeletal muscle cell
Can one motor unit innervate many muscle cells?
What does a lower ratio of lower motor neurons to skeletal muscles mean?
increased dexterity, fine movements
What does a higher ratio of lower motor neurons to skeletal muscles mean?
decreased dexterity, larger movements
What is the process of activation at the neuromuscular junction?
- AP arrives at distal end of LMN
- Depolarization process of AP allows influx of Ca (opens voltage-gated Ca channels), initiating exocytosis
- NT (ACh) released into synaptic cleft
- ACh diffuses across synaptic cleft and activates receptors on motor end plate
- When ACh is released, partial depolarization continues to depolarize the length of the sarcolemma, using voltage gated channels to continue AP (starts w/ ligand gated, continues w/ voltage-gated)
- AP continues to propagate, the change in voltage opens other channels to let Ca into sarcoplasmic reticulum
- presence of excess Ca causes skeletal muscle proteins to slide (contract)
- AChase breaks down ACh in cleft and brings it into the presynaptic neuron to be reused
- muscle relaxes
Each vesicle leaving the presynaptic membrane at the neuromuscular junction contains how many molecules of ACh?
ACh in the synaptic clefts increases 100,000 times after:
release (always a constant leakage of Ach into synaptic cleft)
What is happening during exocytosis at the neuromuscular junction?
vesicle fusion to presynaptic membrane and NT release)
Where is the motor end plate located at the neuromuscular junction?
on postsynaptic membrane of sarcolemma (cell membrane of skeletal mm)
speacialized area that contains ligand-gated channels, containing receptors for ACh
What two types of receptors for ACh are in the sarcolemma of the motor end plate?
- nicotinic receptors
- muscarinic receptors
- almost always respond to ACh
- ligand gated Na channel in MEP
Binding to a nicotinic receptor causes:
influx of Na, causing a partial depolarization of postsynaptic membrane
End plate potential (EPP):
partial depolarization of postsynaptic membrane
Does EPP generate an AP or graded potential?
graded (partial depolarization)
What does the end plate potential equal?
Can EPP illicit AP of skeletal mm?
Can EPSP illicit AP of skeletal mm?
Muscarinic receptors are located on:
parasympathetic postganglionic neurons (ex. cardiac tissue)
Muscarinic receptors are found in which part of the nervous system?
Do AP at the neuomuscular junction have spatial or temporal summation?
Once the muscle is contracted, how does the nervous system avoid rigidity or continuous depolarization at one site?
- AChase enzyme present in synaptic cleft breaks down ACh
- ACh broken down into inactive forms (A and Ch separately) and cannot facilitate depolarization
- Using endocytosis process, A and Ch taken back up into presynaptic membrane of neuron
- it is repackaged and becomes biologically active again to be used in the future
- muscle relaxes