The Neuromuscular Junction

Question 1

What are the Neurons that cause skeletal muscle to contract?

Answer 1

These are known as “Somatic Motor neurons”.

Question 2

Where do Muscle action potentials arise from?

Answer 2

They arise from the Neuromuscular Junction (NMJ).

Question 3

What is a Synapse?

Answer 3

It is a Region where communication occurs between 2 neurons or a Neuron and a Target cell.

Question 4

What is a Synaptic cleft?

Answer 4

This is a gap between Synapses.

Question 5

Why do communicating cells need to use Neurotransmitters?

Answer 5

This is because of the Synaptic cleft & how Action potentials cannot jump the gap between the 2 cells.

Question 6

What is the Molecule (AHC)?

Answer 6

Acetycholine is the molecule inside each Synaptic Vesicle.

They are released by nerve endings and bind to ACHRS causing calcium channels to open.

Question 7

What are the Steps to a Nerve impulse (nerve action potential) electing a muscle action potential?

Answer 7

1: Release of (ACH)
2: Activation of (ACH) receptors
3: Production of muscle action potential
4: Termination of (ACH) activity

Question 8

What are Synaptic Vesicles?

Answer 8

Within the Synaptic End Bulb are hundreds of membrane enclosed sacks called Synaptic Vesicles.
Within the Synaptic vesicles is the Neurotransmitter (ACH).

Question 9

What are Junction folds?

Answer 9

These are the folds within the Motor end plates and are abundant with ACH receptors.

Question 10

What are Motor end plates?

Answer 10

This is the portion of the Sarcolemma opposite of the Synaptic end bulbs.

Question 11

What are Synaptic End Bulbs?

Answer 11

At the NMJ at the end of the motor neuron (Axon terminal) divides into a cluster of Synaptic end bulbs.

Question 12

What is released by the Neuromuscular Junction to create Muscle action potentials?

Answer 12

The Neurotransmiter (ACH).

Question 13

What are Synaptic End Bulbs?

Answer 13

This is the Neural part of the neuromuscular junction.

A portion of the Axon terminal.

Question 14

What happens in the 1st step of The Neuromuscular Junction?

Answer 14

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.

Question 15

What happens in the 2nd step of the Neuromuscular junction?

Answer 15

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.

Question 16

What happens in the 3rd step of the Neuromuscular junction?

Answer 16

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.

Question 17

What happens in the 4th step of The Neuromuscular junction?

Answer 17

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.

Question 18

What stage of the Neuromuscular junction does NA+ flow across the ACH receptor membrane?

Answer 18

Step 2 Activation of ACH receptors.

Question 19

What in the neuromuscular junction triggers a Muscle action potential?

Answer 19

The inflow of NA+ makes the inside of the muscle fibre more positively charged triggering an action potential.

Question 20

How many Nerve impulses are needed per Muscle action potential?

Answer 20

There is 1 Nerve impulse for every Muscle action potential.

Question 21

What breaks down ACH?

Answer 21

An enzyme called ACHE.

Question 22

Where is ACHE located?

Answer 22

In the Extracellular side of the motor end plate membrane.

Question 23

What is a Motor Unit?

Answer 23

A motor Unit is (1 Somatic Motor neuron & all the skeletal Muscle fibres / cells it stimulates).

Question 24

What does the Total strength of contraction depend on?

Answer 24

It depends on how many motor units are activated & how large the motor unit are?