neurotransmission

Question 1

what is a neuromuscular junction?

Answer 1

junctional folds with ACh receptors and cholinesterase enzymes

Question 2

what are end plate potentials?

Answer 2

Depolarization of skeletal muscle fibres caused by neurotransmitters binding to the postsynaptic membrane in the neuromuscular junction.

Synaptic potentials that you can record across the muscle fibre when you activate the end plate

Question 3

how does the size of the EPP change as you move towards the end plate?

Answer 3

gets larger

Question 4

what size EPP can generate an AP?

Answer 4

a large one

Question 5

what are miniature end plate potentials?

Answer 5

small depolarizations of the postsynaptic membrane caused by the release of a single vesicle into the synaptic cleft

Question 6

why don’t mEPPs stimulate an AP?

Answer 6

they’re small depolarisations which do not reach the threshold

Question 7

where can you record mEPPs?

Answer 7

when you’re close to the muscle end plate

Question 8

what does neurotransmitter release in the CNS cause?

Answer 8

EPSPs and IPSPs in the post synaptic cell

Question 9

why do membranes have a negative membrane potential?

Answer 9

bc of the distribution of K+ across the membrane –> tendency of K+ to leave the membrane

Question 10

what receptor does ACh bind to?

Answer 10

nicotinic ACh receptor

Question 11

how many ACh molecules required for Na+ influx?

Answer 11

2

Question 12

what effect does ACh have on the membrane?

Answer 12

depolarises it from negative to positive

Question 13

what is the receptor that is associated with IPSPs?

Answer 13

GABAa receptor

Question 14

how is an IPSP produced?

Answer 14

GABAa receptor is permeable to Cl-
Cl- moves into the membrane and makes it more negative –> hyperpolarisation
harder to fire an AP

Question 15

what neurotransmitter do primary sensory neurons use and what type of NTS are they?

Answer 15

glutamate (fast and modulator)

Question 16

what neurotransmitter do CNS neurons use and what type of NTS are they?

Answer 16

acetylcholine (F+M)
o Amino acids – glutamate, GABA (inhibitory) (both F+M), glycine (inhibitory- F)
o Biogenic amines – noradrenaline (M), 5-HT (F+M), dopamine (M)

Question 17

describe the reflex arc

Answer 17

• 1a afferent reflex – brought about by patellar ligament tap for example
• AP go through dorsal root into the grey matter
• Monosynaptic connection with a homonymous motor neuron in the ventral horn
oEPSPs excite alpha motor neuron and recruit an AP
•Sends an axon out the ventral root
•Sends AP to the same muscle providing the input

Question 18

what gives rise to reciprocal antagonism?

Answer 18

inhibitory interneuron which transmits an inhibitory neurotransmitter

Question 19

what neurotransmitter do inhibitory interneurons use?

Answer 19

glycine

Question 20

put these in order from fastest to slowest;

neurotrophic factor, neurotransmitter, neuromodulator

Answer 20

neurotransmitter - ms
neuromodulator - s-mins
neurotrophic factor - mins/hours

Question 21

what receptors do fast neurotransmitters use?

Answer 21

multimeric (pentameric and tetrameric) receptors that incorporate ion channels

Question 22

what receptors do modulators use?

Answer 22

G-protein coupled receptors

Question 23

what are the 2 classes of action of neurotransmitters

Answer 23

Fast - direct gating of ion channel

Modulatory – activation of G-protein coupled receptor pathway

Question 24

what are the mechanisms involved in the termination of transmitter action?

Answer 24

1. Transmitter breakdown

2. Reuptake using selective transport mechanisms

Question 25

how can neurotransmitters be broken down?

Answer 25

acetylcholinesterase - found in the synaptic cleft and cleaves ACh

selective reuptake mechanisms which terminate the action of the transmitter which run off the Na+ gradient

Question 26

how can acetylcholinesterase be inhibited?

Answer 26

• nerve agents

- medically inhibited by neostigmine, physostigmine etc for treatment of myasthenia gravis

Question 27

what are examples of neurotransmitter reuptake?

Answer 27

glutamate transporters - glutamate taken up into pre/post synaptic terminals and astrocytes. transporters use energy stored in transmembrane Na+ from Na/K pump to uptake glutamate

GABA reuptake - into presynaptic terminals and astrocytes by GATs

Question 28

what are the waves of the muscle action potential recorded by electrical stimulation of peripheral nerve?

Answer 28

o M-wave, direct activation of motor units by electrical stimulation
o H-reflex, electrical equivalent to stretch-reflex
o F-wave, antidromic motor nerve action potentials bouncing off the a-motoneurons

Question 29

what abnormalities can be shown by evoked muscle action potentials?

Answer 29

o Peripheral demyelination
o Carpal tunnel entrapment
o Myasthenia Gravis (neuromuscular disease)
o Lambert-Eaton myasthenic syndrome