PSY1003 WEEK 2 PART 1

Question 1

define resting potential

Answer 1

inside of neuron (-70mV) is negatively charged compared to outside and described as ‘polarised’

Question 2

very briefly explain what causes resting membrane potential

Answer 2

due to uneven ion distribution across membrane as more negative inside and positive on outside

Question 3

how can we record a resting membrane potential

Answer 3

position one electrode tip inside neuron and other on outside

Question 4

explain in depth how a resting membrane potential is established

Answer 4

1. at rest: membrane impermeable to ions (not K+). more Na+ outside than inside and more K+ inside than outside, maintained via ion channels
2. electrostatic pressure from resting membrane potential attracts positive Na+ into neuron (random motion down conc gradients also occurs)
3. flood of Na doesn’t happen as Na+ channels are shut
4. K+ flow down chemical conc gradient across membrane via diffusion
5. ## K+ leaving producing electrical current meaning positive charge on one membrane side, negative charge on other causing potential difference “membrane potential”
   1. Na+/K+ pump transports 3Na+ out and 2K+ in
   2. as more positive charge leaves than enters causes potential drop

Question 5

define depolarisation

Answer 5

membrane potential is made less negative

Question 6

define hyperpolarisation

Answer 6

membrane potential is made more negative

Question 7

outline in 5 steps, how an action potential is generated

Answer 7

1. EPSP causes cell depolarisation to an excitation threshold, causing v/gated Na+ channels to open
2. Na+ enters and polarity reverses to +30mV inside neuron
3. so Na+ channel close, K+ channel open, so can restore resting membrane potential (starting repolarisation)
4. after repolarisation, K+ channels slowly close so lots of K+ flow out causing brief period of hyperpolarisation
5. if membrane is depolarised beyond threshold, generates AP

Question 8

define propagation

Answer 8

continuous generation of AP along axon

Question 9

what does it mean when AP is non-decremental

Answer 9

doesn’t grow weaker the further it travels along axon

Question 10

explain how AP travels down axon

Answer 10

1. once generated travels passively along axonal membrane to closed v/gated Na+ channels and opens them
2. Na+ flows in, generating AP
3. conducted passively to next Na+ channel etc
4. AP generation near axon hillock triggers excitation waves that spread passively back through soma and dendrites

Question 11

is AP conduction slower or faster than postsynaptic potential

Answer 11

slower due to EPSP and IPSP conduction being passive, but axonal AP conduction being active

Question 12

define antidromic conduction

Answer 12

generation of AP which travels along axon to some due to sufficient intensity of electrical stimulation applied to terminal end of axon

Question 13

define orthodromic conduction

Answer 13

axonal conduction in normal direction from soma to terminal buttons

Question 14

define saltatory conduction

Answer 14

transmission of AP in myelinated axon