Neurons: Action potentials

Question 1

what happens if you decrease concentration gradient of ions

Answer 1

RMP further away from that ion’s equilibrium potential

Question 2

what happens if you increase the concentration gradient

Answer 2

RMP closer to that ions equilibrium potential

Question 3

what happens if you increase permeability

Answer 3

RMP closer to that ion’s equilibrium potential

Question 4

hyperpolarisation

Answer 4

inside of the cell becomes more negative than RMP (potential in cell moves closer to EK and away from ENa)

Question 5

depolarisation

Answer 5

inside of cell becomes less negative than RMP (potential in cell moves away from EK and closer to ENA)

Question 6

Action potential

Answer 6

a brief fluctuation in membrane potential caused by a transient opening of voltage gated ion channels which spreads like a wave along an axon
- occur when threshold voltage reached (~-55mV)
- frequency encodes information

Question 7

stage 1 of action potential

Answer 7

stimulus reaches and surpasses threshold, slowly depolarises (stimulus = physical [electric current, mechanical stretch] or chemical [drug or synaptic exitation]). stimulus will be from non-voltage gated ion channels. Then… fast depolarisation, goes past mV called the overshoot

Question 8

stage 2 of action potentials

Answer 8

repolarisation - after peak reached, it goes back down and potential becomes more negative.

Question 9

stage 3

Answer 9

after hyperpolarisation = running a bit below threshold. at this point another stimulus can occur but will need to be greater than the first

Question 10

molecular events for Na channel activation

Answer 10

at RMP, voltage sensing activation gate is closed, inactivation gate is open.
at threshold, activation gate opens

Question 11

molecular events for Na channel inactivation

Answer 11

inside potential becomes positive so Na channels inactivate during repolarisation and inactivation gate closes, then when it goes back to RMP, inactivation gate opens and activation gate closes

Question 12

electrical stimuli and action potentials

Answer 12

External: experimental - battery
Internal: physiological - synaptic potentials

Question 13

external activation of APs

Answer 13

1) outside axon from + to -
2) across membrane and inside axon which changes RMP

Question 14

passive spread of potential

Answer 14

when subthreshold, if local depolarisation, postiive charges want to spread to negative and negative wants to spread to positive (depolarisation of adjacent parts of axon). dissipates quickly

Question 15

axons

Answer 15

unmyeinated: smaller, slow transmission (AP must be regenerated at every point), and continuous (every section)
myelinated: large, transmit fast, and occurs in large steps (saltatory, jump before the next AP)

Question 16

myelin sheath

Answer 16

by olgiodendrocytes in CNS and schwann in PNS
node of ranvier are the unmyelinated parts. It increases AP conduction speed because APs only need to be generated at the nodes of ranvier

Question 17

benefits of myelination

Answer 17

• less passive current loss
• less time to generate APs
• less energy to maintain gradient
  con - larger

Question 18

why does AP conduct in only one direction under physiological condition

Answer 18

because of the absolute refractory in the previous node. passive conduction going to the previous node won’t trigger another AP

Question 19

PNS

Answer 19

axons and cell bodies of sensory neurons (input)
axons of motoneurons (output)
neurons of autonomic nervous system