Signalling and Action

Question 1

What is conduction?

Answer 1

the sending of APs along axons to allow the neuron cell body to communicate with its own terminals

Question 2

What is the depolarisation to the threshold Em facilitated by?

Answer 2

• blocking efflux of intracellular K+ ions
• enhancing the influx of extracellular Na+ ions
• release of ACh at the NMJ

Question 3

What are the 7 phases of an AP?

Answer 3

1. RMP (~-60mV)
2. Em is depolarised by excitatory neurotransmitter opening ligand gated ion channels
3. voltage gated Na+ channels are activated and Em reaches threshold (-40mV)
4. rising phase via rapid Na+ influx
5. overshoot phase since inside of the cell becomes more positive than the outside reversing the Em polarity
6. voltage gated Na+ channels are inactivated and voltage gated K+ channels are open, which causes repolarisation
7. Em returns to RMP as voltage gated K+ channels close

Question 4

What is RMP determined by?

Answer 4

the distribution of K+, Na+ and Cl- ions

Question 5

How does hypokalaemia affect RMP?

Answer 5

it impairs the ability to generate APs at the NMJ leading to muscle weakness and paralysis

Question 6

What are 4 the steps of synaptic transmission at the NMJ?

Answer 6

1. AP arrives at the presynaptic axon terminal which depolarises the presynaptic membrane and opens voltage gated Ca2+ channels
2. Ca2+ influx causes the fusion of the synaptic vesicle with the presynaptic membrane leading to the release of ACh into the synaptic cleft
3. ACh binds to the postsynaptic nicotinic ligand gated receptor which leads to influx of Na+ into the postsynaptic membrane which depolarises
4. this generates further APs through voltage gated sodium channels

Question 7

What is hyperpolarisation of the RMP due to?

Answer 7

decreased extracellular K+ levels which causes the skeletal muscle membrane to become less excitable exhibiting a decreased ability to generate action

Question 8

What is the relationship between stimulus strength and AP frequency?

Answer 8

the greater the stimulus strength, the greater the frequency of APs

Question 9

What are the 4 steps of transduction?

Answer 9

1. application of stimulus to the receptor in the periphery results in depolarisation of the receptor membrane
2. receptor potential travels to the trigger zone of the associated primary afferent and depolarisation generates an AP
3. AP discharge is propagated along the axon
4. AP discharge reaches the axon terminal where it triggers the release of transmitter which affects the next neuron in the CNS

Question 10

What does transduction of noxious stimulus involve?

Answer 10

depolarisation of the receptor membrane, which travels to the trigger zone on the associated axon where it leads to the generation of an AP

Question 11

What is a sensory receptor?

Answer 11

a sensory nerve ending that recognises a stimulus, and in response, initiates sensory transduction by creating APs in the same cell, or in an adjacent zone

Question 12

What are mechanoreceptors sensitive to?

Answer 12

mechanical energy e.g. touch, pressure, vibration, stretch and sound

Question 13

What are nociceptors sensitive to?

Answer 13

tissue damage e.g. noxious stimuli

Question 14

What are chemoreceptors sensitive to?

Answer 14

chemicals e.g. oxygen, pH glucose

Question 15

What are photoreceptors sensitive to?

Answer 15

light

Question 16

What are thermoreceptors sensitive to?

Answer 16

varying degrees of heat

Question 17

What are proprioceptors sensitive to?

Answer 17

sense position of body in space