lecture 27 - generation of AP

Question 1

2 ways to change the potential inside cells

Answer 1

1. change in membrane permeability 2. ion concentrations change

Question 2

hyperpolarisation

Answer 2

potential inside cell becomes more negative. i.e potential moves closer to EK+ and further from ENa+ (e.g. -70 to -75)

Question 3

depolarisation

Answer 3

potential inside cell becomes less negative i.e. potential moves closer to ENa+ and further from EK+ (e.g. -70 to -60)

Question 4

action potential =

Answer 4

an AP is a brief fluctuation in membrane potential, caused by a transient opening of voltage-gated ion channels, which spreads like a wave along an axon

Question 5

when will an action potential occur?

Answer 5

when the membrane potential reaches the threshold = -55mV

Question 6

how is information carried by an AP?

Answer 6

information is carried in the frequency of the AP, NOT size of AP

Question 7

APs are the key element in the process of signal transmission along axons true/false

Answer 7

TRUUUUUU

Question 8

Outline steps of AP

Answer 8

1. slow depolarisation caused by stimulus
2. once MP reaches threshold of -55mV (from -65mV), fast depolarisation to +30mV
3. repolarisation
4. AHP (after-hyperpolarisation)

Question 9

absolute refractory period =

Answer 9

period of time coinciding with the Na+ channel activation and inactivation. A second action potential cannot be initiated during this time, even with a strong stimulus.

Question 10

relative refractory period =

Answer 10

period of time when voltage-gated K+ channels are still open after inactivated Na+ channels have returned to resting state. AP can only be generated with a larger than normal stimulus.

Question 11

what is overshoot?

Answer 11

reversal of polarisation, when MP goes from -ve to +ve

Question 12

2 types of stimulus

Answer 12

1. chemical (synaptic excitation) 2. physical (electric current, light, stretch)

Question 13

what happens once threshold is reached

Answer 13

sudden activation (opening) of voltage-gated Na+ channels (PNa+ increases). Rapid influx of Na+.

Question 14

how does the permeability of Na change in comparison to K, once threshold is reached?

Answer 14

goes from resting of PK+/PNa+ = 40/1 to 1/20. this causes MP to shift more towards Na+. overshoots to +30mV.

Question 15

opening of voltage-gated Na+ channels short lived because… (two causes)

Answer 15

1. inside potential becomes more positive (so electric gradient is decreasing) 2. Na+ channels inactivate (inactivation gate plugs channel)

Question 16

what follows inactivation of voltage-gated Na+ channels?

Answer 16

TRANSIENT opening of voltage-gated K+ channels, leading to repolarisation and after-hyperpolarisation (AHP)

Question 17

how does the permeability of K change in comparison to Na, in AHP?

Answer 17

PK+/PNa+ becomes 100:1

Question 18

why is the flow of Na+ into the cell, via voltage-gated channels so rapid?

Answer 18

Na+ is moving down both its electrical and its chemical gradient.

Question 19

does the AP amplitude stay constant or change depending on stimulus intensity

Answer 19

AP amplitude stays constant at ~100mV. the intensity of the stimulus doesn’t matter, as long as it is SUPRATHRESHOLD

Question 20

what happens if the stimulus is subthreshold?

Answer 20

nothing. These stimuli are graded. Each AP is an “all or nothing” event

Question 21

when current flows into the cell, there is a _____ ________. When current flows out of the cell, there is a _____ ________.

Answer 21

when current flows into the cell, there is a _local_ _hyperpolarisation_. When current flows out of the cell, there is a _local_ _depolarisation_.

Question 22

action potentials are first generated in the axon _____ _______ (also called axon _______) which has the ______ threshold, and thus serves as the trigger zone for action potentials

Answer 22

action potentials are first generated in the axon _initial_ _segment_ (also called axon _hillock_) which has the _lowest_ threshold, and thus serves as the trigger zone for action potentials

Question 23

what are excitatory postsynaptic potentials (EPSPs)?

Answer 23

depolarising currents which spread PASSIVELY from the dendtrites to evoke the depolarisation to threshold (-55mV)

Question 24

how are APs transmitted along the axon?

Answer 24

ACTIVELY, away from cell body/soma

Question 25

in which region would voltage-gated K+ channels open and then close?

Answer 25

Voltage-gated K+ channels open at stage 2 (repolarisation) and close at the end of stage 3 (AHP).

Question 26

which region of the curve shows where P_K is less than P_Na ?

Answer 26

stage 1

Question 27

produced by opening of channels in the postsynaptic membrane that are permeable to several cations (Na+, K+ and often Ca2+).

Answer 27

EPSPs

Question 28

produced by opening of channels in the postsynaptic membrane that are permeable to K+ and Cl-

Answer 28

IPSPs