Pharmacology: Action Potentials

Question 1

depolarisation

Answer 1

membrane becomes more positive

Question 2

hyperpolarisation

Answer 2

membrane becomes less positive

Question 3

direction of change in potentials depends on

Answer 3

direction of ion movement and the charge carried

Question 4

what drives the passive movement of ions through ion channels

Answer 4

electrochemical gradient

Question 5

why do Na+ ions move inward

Answer 5

the concentration and electrical gradients draw Na+ inwards

Question 6

what is the Na+ driving force

Answer 6

when ENa+ becomes mores -ve than Vm inward Na+ movement can occur

Question 7

why do K+ ions flow outward

Answer 7

the outward conc. gradient is stronger than the inward electrical gradient

Question 8

what is the K+ driving force

Answer 8

when EK+ becomes mores +ve than Vm outward K+ movement can occur

Question 9

when Na+ channels open where in the membrane potential driven towards

Answer 9

ENa+ - more positive

depolarisation

Question 10

when K+ channels open where in the membrane potential driven towards

Answer 10

EK+ - more negative

hyperpolarisation

Question 11

what type of gated channels are responsible for action potentials

Answer 11

voltage-gated ion channels (VGICs)

Question 12

what are action potentials

Answer 12

brief electrical signals where the polarity of the membrane is momentarily reversed allowing signalling over long distances

Question 13

when is an AP generated

Answer 13

when a threshold is reached

Question 14

when are Na+ channels activated by membrane depolarisation and when are K+ channels

Answer 14

• Na+, rapidly

- K+, with a slight delay

Question 15

the activation of Na+ channels is what type of feedback and what does this mean

Answer 15

• +ve feedback

- activation of Na+ channels causes the activation of more Na+ channels

Question 16

the activation of K+ channels is what type of feedback and what does this mean

Answer 16

• -ve feedback

- K+ channel activation turns of the stimulus for opening and therefore stops the opening of more K+ channels

Question 17

what happens to Na+ channels during maintain depolarisation

Answer 17

enter a non-conducting, inactivated state

Question 18

what is needed for an Na+ channel to enter the closed state

Answer 18

repolarisation

Question 19

absolute refractory and why

Answer 19

no stimulus can elicit a second AP, all Na+ channels in inactivated state

Question 20

relative refractory and why

Answer 20

a strong stimulus can elicit a second AP, mixed closed and inactivated Na+ channels

Question 21

draw an action potential and label each stage

Answer 21

** notes

Question 22

why do passive signals diminish

Answer 22

nerve cell membranes are ‘leaky’ and therefore passive signals don’t get very far do to current loss across the membrane and a decrease in potential

Question 23

action potentials have a _ amplitude

Answer 23

constant

Question 24

what happens when an axon is less ‘leaky’

local spread and conduction velocity

Answer 24

the local current spread is greater therfore there is an increase in AP conduction velocity

Question 25

how is passive spread decreased

Answer 25

• axon diameter is increased, increases current spread

- insulting material decreases leak of current

Question 26

what are insulated axons called

Answer 26

myelinated axons

Question 27

in what type of axons do currents spread faster

Answer 27

myelinated compared to non-myelinated

Question 28

name the insulating material in the

• PNS
• CNS

Answer 28

• myelin

- oligodendrocytes

Question 29

describe what happens to the AP in terms of nodes of Raniver

Answer 29

the AP jumps from one to the next, this increases conduction velocity

Question 30

where are nodes of Raniver

Answer 30

between myelin sheaths

Question 31

what clusters at nodes of Raniver

Answer 31

Na+ channels - increasing the conduction velocity at each one