Lecture 6- NMJ Flashcards

1
Q

what is the NMJ?

A
  • a specialist synapse between an alpha motor neuron and a muscle fiber (muscle cell)
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

what does the ‘motor unit’ consist of?

A
  • alpha motor neuron and it’s axon
  • all the skeletal muscle fibers that it innervates

NB - one alpha motor neuron innervates many muscle fibers

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What is the function of the NMJ?

A
  • it allows a motor neuron to** transmit action potentials **(AP’s) to a muscle fiber. which causes contraction
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

what are the main features of a NMJ?

ie structure

A
  1. alpha motor neuron - axon terminal
  2. terminal bouton
  3. synaptic vesicles (with NT’s)
  4. motor end plate
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What **neurotransmitter **is involved in the NMJ synapse?

A
  • Ach - acetylcholine
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

what 2 molecules is Ach synthesised from?

A
  1. Acetyl CoA
  2. choline
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Describe Ach synthesis and storage.

A

Synthesis
* Ach is synthesised from choline and acetyl co A
* the enzyme ChAT converts these 2 molecules to acetylcholine
Storage
* Ach is stored in synaptic vesciles in the axon terminal of the motor neuron

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

When Ach is released from the synaptic vesicles, what happens immediately?

A
  • it is immediately broken down by ACHE
  • Choline is actively transported back to the nerve terminal, where it forms the substrate for ChAT
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What process best describes how the neurotransmitter is released at the NMJ?

A
  • exocytosis
  • form of transport in which a cell transports molecules out of the cell
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Describe the **sequence of events at the NMJ **that lead to an action potential in a muscle fiber

A
  1. an action potential reaches the axon terminal, causing depolarisation
  2. depolarisation causes the opening of voltage gated Ca2+ channels
  3. this allows an influx of Ca2+
  4. Ca2+ ions bind to** synaptotagmins** on the synaptic vesicles
  5. this causes the vesicles to** fuse with the membrane** and** Ach is released** from the motor neuron into the synaptic cleft
  6. Ach binds to nicotinic receptors on the sarcolemma
  7. as the receptors are ionotropic receptors (ligand gated ion channels), they allow Na2+ and K+ entry into muscle fiber - EPP
  8. the EPP** exceeds threshold** and all voltage gated Na+ channels open
  9. AP propagates through muscle fiber
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

what does** MEPP** mean?

A
  • minature end plate potential
  • the smallest amount of stimulation that one neuron can send to another neuron
  • blips in the resting membrane potential
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

what is the MEPP **amplitude **called?

A

quantal size

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What is the safety factor of the MNJ defined as?

A
  • refers to the ability of the NMJ transmission to remain effective under various physiological conditions and stresses
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

how many synaptic vesicles roughly are released form the presynaptic neuron after the influx of Ca2+? & what does this release cause?

A

roughly about 50 synaptic vesicles
* this release causes a production of an EPP which is at least 5 times as large a one required to trigger an AP of a muscle fibre

How well did you know this?
1
Not at all
2
3
4
5
Perfectly