Action Potentials

Question 1

resting membrane potential

Answer 1

potential difference which exists across membrane of all cells

Question 2

RMP facts

Answer 2

range 20-90mV
ICF negative
equal numbers of +ve and -ve in ECF and ICF

Question 3

which ion goes in / which leaves cell

Answer 3

Na+ goes in K+ leaves

Question 4

difference in permeability in ions for cell

Answer 4

Na+ resting membrane is impermeable
K+ resting membran is very permeable

Question 5

diffusion gradient, what occurs

Answer 5

force of Na+ in, K+ out
diffusion of K+ leaves excess of -ve charge inside cell
potential gradient arising from diffusion is the resting mebrane potential

Question 6

how does the resting membrane potential arise

Answer 6

due to the seperation of charges on either side of the membrane
diffusion of K+ from cell interior through K+ channels
small amount of Na+ leaks into cell is expelled by Na+/K+ pump

Question 7

Na+/K+ pump role in ions charge

Answer 7

exchanges unequal numbers of Na+ and K+
moves 3Na+ outwards, 2K+ inwards [+1 outwards charge]
Na+/K+ is electrogenic

Question 8

action potential threshold

Answer 8

-55mV

Question 9

rising and falling phase of AP

Answer 9

rising - Na+ influx
falling - K+ efflux
-55mV, reversible RMP, overshoot from 0, influx of sodium then efflux of potassium

Question 10

gate opening channels

Answer 10

ligand, voltage

Question 11

ion selective channels

Answer 11

Na+, K+, Ca2+

Question 12

AP is a ….. or ……

Answer 12

all or nothing event, amplittude is independent of stimulus

Question 13

at threshold of AP

Answer 13

voltage gated Na+ channels open, Na+ diffuse in -> further depolarisation
positve feedback

Question 14

at peak of AP

Answer 14

Na+ channels close, voltage gated K+ channels open, K+ diffuses out -> repolarisation
return to RMP

Question 15

refractory period definition

Answer 15

neurons cannot generate another AP until first one is done
period of excitability

Question 16

why does the refractory period occur

Answer 16

due to inactivation of Na+ voltage channels, inactivation gates are shut so Na+ cannot diffuse into neuron

Question 17

consequences of refractory period

Answer 17

limits maximum firing frequency of AP in neurons
ensures unidirectional propagation of AP
prevents summation of AP
prevents summation of contractions in cardiac muscle = cardiac AP lasts as long as ventricular contraction

Question 18

how does an AP crawl along axon

Answer 18

in one direction
from ECF to ICF in +ve to -ve directions

Question 19

how does axon diameter affect speed

Answer 19

speed increases with axon diameter
large axons conduct impulses quicker than small
rapid conduction with very large ones
myelin increases speed of AP

Question 20

does myelin increase or decrease speed of axons

Answer 20

myelinisation creates fast axons, without having to increase diameter that much

Question 21

myelinated axon

Answer 21

increased AP propagation
cell membranes wrapped around axon
laid down by glial cells, insulating layer, reducing leakage
interupted at interval = Nodes of Ranvier

Question 22

nodes of ranvier

Answer 22

myelin sheath interrupted at intervals
here the axon membrane exposed to ECF and ion flow can occur

Question 23

A beta funtion

Answer 23

mechanoreceptors

Question 24

a delta function

Answer 24

mechano, thermo, noci, chemo

Question 25

c fibres function

Answer 25

unmyelinated, mechano, themro, noci