How Nerves Work 5

Question 1

Describe in full how an action potential would produce a reaction at a neuromuscular junction

Answer 1

A motor action potential travels along and produces a suitable threshold for calcium to enter the cell through voltage gated channels in presynaptic terminals. This triggers fusion of vesicles and acetylcholine to be released (calcium dependent exocytosis) which diffuses across the synaptic cleft and binds to nicotinic receptors on ligand gated channels which open up and sodium enters the cell to depolarise it which evokes a EPSP. This is a massive end plate potential. This means there is a local current between the end plate and the adjacent plasma membrane which initiates a muscle fibre action potential along the membrane by opening voltage gated sodium channels.

Question 2

Why are junctions folds important in the sarcolemma?

Answer 2

All action receptor receptors are on top of the folds which start a Graded potential so it doesn’t have far to travel to the sodium voltage gated channels at the bottom of the folds so a threshold can ALWAYS be reached.

Question 3

What is acetylcholinesterase?

Answer 3

Removed acetylcholine to avoid build up of it which can lead to spasms of the muscle.

Question 4

Explain what happens in CNS synapses for an action potential to elicit a reaction

Answer 4

The action potential reaches the terminal and causes calcium voltage gated channels to open and calcium enters the axon terminal. The neurotransmitter diffuses across the synaptic cleft and binds to postsynaptic receptors. This causes a reaction then the neurotransmitter is removed from the synaptic cleft.

Question 5

Name different types of CNS neurotransmitters

Answer 5

Acetylcholine
Noradrenaline
Dopamine
Seratonine
Histamine
These are all amines
Glutamate (important excitory Transmitter)
GABA
Glycine (important inhibitory transmitter)
Peptides
ATP
Adenosine
NO (lipophilic so won’t stay in vesicles so has to be produced on demand and doesn’t use calcium dependant exocytosis)
Each of these neurotransmitters can have several different receptors.

Question 6

Name 3 different anatomical arrangements of CNS synapses

Answer 6

Axo-somatic (synapse onto soma)
Axo-dendritic (synapse onto dendrites)
Axo-axonal (synapse onto presynaptic axon terminal)

Question 7

Differentiate between convergence and divergence in relation to synaptic connectivity

Answer 7

Convergence involves one cell being synapsed onto by lots of cells whilst divergence is one cell synapsing onto lots of cells.

Question 8

Describe feedback inhibition in terms of CNS

Answer 8

A neurone can inhibit itself once it has fired an action potential

Question 9

Define monosynaptic and polysynaptic in terms of nerve pathways

Answer 9

Monosynaptic is the simplest reflex and is produces a fixed response (no other influences from other cells). Polysynaptic involves lots of pathways due to influence from other cells so has a far less predictable response.

Question 10

Name reasons why the CNS response is more complicated than the NMJ

Answer 10

There are a range of neurotransmitters, a range of postsynaptic Potentials, smaller Potentials (so need synaptic integration), the anatomical arrangement changes and the connectivity of neurones varies.