The Neuromuscular Junction Flashcards
What are the Neurons that cause skeletal muscle to contract?
These are known as “Somatic Motor neurons”.
Where do Muscle action potentials arise from?
They arise from the Neuromuscular Junction (NMJ).
What is a Synapse?
It is a Region where communication occurs between 2 neurons or a Neuron and a Target cell.
What is a Synaptic cleft?
This is a gap between Synapses.
Why do communicating cells need to use Neurotransmitters?
This is because of the Synaptic cleft & how Action potentials cannot jump the gap between the 2 cells.
What is the Molecule (AHC)?
Acetycholine is the molecule inside each Synaptic Vesicle.
They are released by nerve endings and bind to ACHRS causing calcium channels to open.
What are the Steps to a Nerve impulse (nerve action potential) electing a muscle action potential?
1: Release of (ACH)
2: Activation of (ACH) receptors
3: Production of muscle action potential
4: Termination of (ACH) activity
What are Synaptic Vesicles?
Within the Synaptic End Bulb are hundreds of membrane enclosed sacks called Synaptic Vesicles.
Within the Synaptic vesicles is the Neurotransmitter (ACH).
What are Junction folds?
These are the folds within the Motor end plates and are abundant with ACH receptors.
What are Motor end plates?
This is the portion of the Sarcolemma opposite of the Synaptic end bulbs.
What are Synaptic End Bulbs?
At the NMJ at the end of the motor neuron (Axon terminal) divides into a cluster of Synaptic end bulbs.
What is released by the Neuromuscular Junction to create Muscle action potentials?
The Neurotransmiter (ACH).
What are Synaptic End Bulbs?
This is the Neural part of the neuromuscular junction.
A portion of the Axon terminal.
What happens in the 1st step of The Neuromuscular Junction?
Release of ACH:
Arrival of a nerve impulse at the “Synaptic End bulbs” stimulates voltage gate channels to open.
Calcium flows into the channels.
During the Exocytosis Synaptic vesicles fuse with the Motor neurone plasma membrane.
What happens in the 2nd step of the Neuromuscular junction?
Activation of ACH receptors:
Binding of 2 molecules of ACH to the receptor on the Motor neurone end plate opens an ion channel in the ACH receptor.
once the Channel is open NA+ can flow across the membrane.
What happens in the 3rd step of the Neuromuscular junction?
Production of Muscle action potential:
The inflow of NA+ makes the fiber more + charged.
The action potential then travels along the Sarcolemma and into the T tubules.
This causes calcium to be released and the muscle contracts.
What happens in the 4th step of The Neuromuscular junction?
Termination of ACH Activity:
The effects of ACH binding only last briefly as ACH is broken down very quickly.
ACHE is located in the extracellular side of the motor end plate.
What stage of the Neuromuscular junction does NA+ flow across the ACH receptor membrane?
Step 2 Activation of ACH receptors.
What in the neuromuscular junction triggers a Muscle action potential?
The inflow of NA+ makes the inside of the muscle fibre more positively charged triggering an action potential.
How many Nerve impulses are needed per Muscle action potential?
There is 1 Nerve impulse for every Muscle action potential.
What breaks down ACH?
An enzyme called ACHE.
Where is ACHE located?
In the Extracellular side of the motor end plate membrane.
What is a Motor Unit?
A motor Unit is (1 Somatic Motor neuron & all the skeletal Muscle fibres / cells it stimulates).
What does the Total strength of contraction depend on?
It depends on how many motor units are activated & how large the motor unit are?
