AWABS - Action Potentials

Question 1

Resting membrane potential across cell membrane

Answer 1

-70 mV

Question 2

What does resting membrane potential depend upon

Answer 2

Selective membrane permeability to different ions

Different ionic concentrations inside and outside the cell

Question 3

Permeability at rest

Answer 3

Freely permeable to potassium

Not permeable to sodium (although some might leak in)

Question 4

Potassium concentrations intra and extra cellularly

Answer 4

Inside cell 150 mmol/L
Outside cell 5 mmol/L

K+ freely diffuses out of cell - so cell becomes more negative until equilibriates

Question 5

Large intracellular anions

Answer 5

Proteins
Phosphates
Sulphates

Question 6

Gibbs-Donnan effect

Answer 6

Large insoluble molecules with negative charge which cannot cross membrane

Results in asymmetrical distribution of permeable ions

Question 7

Sodium attributes

Answer 7

Largely extracellular
Some leaks into cell

Na-K ATPase active transport of Na+ out of cell in exchange for K+ (3:2)

Question 8

Role of Na–K ATPase

Answer 8

Maintains Na+ and K+ concentrations

Otherwise resting membrane potential would dissipate

Question 9

Nernst equation definition

Answer 9

Calculates potential difference that any ion would produce if the membrane would be freely permeable to it (Equilibrium potential)

Question 10

Goldman equation

Answer 10

Question 11

Threshold potential definition

Answer 11

Level at which depolarisation is sufficient and fast voltage gated ion channels open

Influx of Na+ ions causes intracellular charge to become positive and then closes the ion channels

Question 12

Threshold potential value

Answer 12

10-15 mV

Question 13

Action of depolarisation of K+

Answer 13

Depolarisation opens voltage gated K+ channels allowing movement of K+ out of cell along concentration gradient

Slower process - allows return to resting membrane potential / repolarisation

Na-K ATPase restores NA+ and K+ concentration gradients

Question 14

Production of action potential

Answer 14

Depolarisation causes similar changes in adjacent membrane leading to waves of Na+ channel opening

All or nothing response

Question 15

Action potential diagram with channel opening / closing

Answer 15

Question 16

Alternate diagram of action potential with channel pictures

Answer 16

Question 17

Permeability graph of Na+ vs K+ over time

Answer 17

K+ has higher baseline as at rest freely permeable

Question 18

Saltatory conduction

Answer 18

In large myelinated nerves action potential conduction is not continuous along length of the fibre but jumps along from point to point

Question 19

Myelination

Answer 19

Nerves covered by fatty layer (overlapping Schwann cells)

Question 20

Advantages of myelination

Answer 20

Increases conduction velocity
Small diameter (saves space)
High metabolic efficiency

Question 21

Why myelination increases metabolic efficiency

Answer 21

Less Na-K ATPase action required to restore gradients

Question 22

Nerve fibre classifications and conduction velocities / diameters

And factors which increase conduction velocity

Answer 22

Question 23

Graph of different nerve fibre classification and conduction

Answer 23

Question 24

Rheobase definition

Answer 24

?Minimal continuous amplitude that will result in depolarisation

Question 25

Chronaxie definition

Answer 25

Minimum time required for an electric current at 2x Rheobase to stimulate a muscle or neuron

Question 26

Cardiac action potential ion differences

Answer 26

Calcium ions are also important along with Na+ and K+

Question 27

Cardiac action potential types

Answer 27

Question 28

Phases of fast type cardiac action potentials

Answer 28

Question 29

Calcium ion movements in Phase 1 and Phase 2 of fast type cardiac action potentials

Answer 29

Influx of Ca2+ via slow L type calcium channel

Question 30

Re-stablishing concentration gradients in Phase 4 of fast type cardiac action potential

Answer 30

ATPase active transporter - Na+ and Ca2+ ions removed from cell in exchange for K+ ions

Question 31

Excitability of cardiac cells

Answer 31

Question 32

Slow response cardiac action potential phases

Answer 32

No Phase 1
Phase 2 extremely brief

Question 33

Phase 0 (rapid depolarisation) of fast vs slow cardiac action potentials

Answer 33

Fast - rapid depolarisation caused by sodium ion influx

Slow - rapid depolarisation caused by calcium ion influx

Question 34

Automaticity definition

Answer 34

Ability to depolarise spontaneously

Seen in SA node, AV node and His-Purkinje system

Question 35

Rhythmicity definition

Answer 35

Regular discharge of action potential

Question 36

Automaticity effects in phase 4 of cardiac action potential

Answer 36

Increase in slope in phase 4 reduces time taken to reach threshold potential so increases rate

Question 37

Effect of threshold potential becoming less negative, or increased hyperpolarisation (so membrane potential more negative) on cardiac action potential pacemaker rate

Answer 37

Slows pacemaker rate as longer time taken to reach threshold potential

Question 38

Axon classification

Answer 38

Question 39

Goldman-Hodgkin-Katz equation use

Answer 39

Examines the effects of multiple different ions acting across a membrane

Similar concept to Nernst equation but accounts for the differences in membrane permeability of the ions

Question 40

Communication between neurones

Answer 40

Secrete communication transmitter chemicals across synapse

Question 41

Axoplasmic flow

Answer 41

Neurotransmitters are synthesised in the cell body and transported down axon to synaptic ends