AWABS - Action Potentials Flashcards
Resting membrane potential across cell membrane
-70 mV
What does resting membrane potential depend upon
Selective membrane permeability to different ions
Different ionic concentrations inside and outside the cell
Permeability at rest
Freely permeable to potassium
Not permeable to sodium (although some might leak in)
Potassium concentrations intra and extra cellularly
Inside cell 150 mmol/L
Outside cell 5 mmol/L
K+ freely diffuses out of cell - so cell becomes more negative until equilibriates
Large intracellular anions
Proteins
Phosphates
Sulphates
Gibbs-Donnan effect
Large insoluble molecules with negative charge which cannot cross membrane
Results in asymmetrical distribution of permeable ions
Sodium attributes
Largely extracellular
Some leaks into cell
Na-K ATPase active transport of Na+ out of cell in exchange for K+ (3:2)
Role of Na–K ATPase
Maintains Na+ and K+ concentrations
Otherwise resting membrane potential would dissipate
Nernst equation definition
Calculates potential difference that any ion would produce if the membrane would be freely permeable to it (Equilibrium potential)
Goldman equation
Threshold potential definition
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
Threshold potential value
10-15 mV
Action of depolarisation of K+
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
Production of action potential
Depolarisation causes similar changes in adjacent membrane leading to waves of Na+ channel opening
All or nothing response
Action potential diagram with channel opening / closing
Alternate diagram of action potential with channel pictures
Permeability graph of Na+ vs K+ over time
K+ has higher baseline as at rest freely permeable
Saltatory conduction
In large myelinated nerves action potential conduction is not continuous along length of the fibre but jumps along from point to point
Myelination
Nerves covered by fatty layer (overlapping Schwann cells)
Advantages of myelination
Increases conduction velocity
Small diameter (saves space)
High metabolic efficiency
Why myelination increases metabolic efficiency
Less Na-K ATPase action required to restore gradients
Nerve fibre classifications and conduction velocities / diameters
And factors which increase conduction velocity
Graph of different nerve fibre classification and conduction
Rheobase definition
?Minimal continuous amplitude that will result in depolarisation
Chronaxie definition
Minimum time required for an electric current at 2x Rheobase to stimulate a muscle or neuron
Cardiac action potential ion differences
Calcium ions are also important along with Na+ and K+
Cardiac action potential types
Phases of fast type cardiac action potentials
Calcium ion movements in Phase 1 and Phase 2 of fast type cardiac action potentials
Influx of Ca2+ via slow L type calcium channel
Re-stablishing concentration gradients in Phase 4 of fast type cardiac action potential
ATPase active transporter - Na+ and Ca2+ ions removed from cell in exchange for K+ ions
Excitability of cardiac cells
Slow response cardiac action potential phases
No Phase 1
Phase 2 extremely brief
Phase 0 (rapid depolarisation) of fast vs slow cardiac action potentials
Fast - rapid depolarisation caused by sodium ion influx
Slow - rapid depolarisation caused by calcium ion influx
Automaticity definition
Ability to depolarise spontaneously
Seen in SA node, AV node and His-Purkinje system
Rhythmicity definition
Regular discharge of action potential
Automaticity effects in phase 4 of cardiac action potential
Increase in slope in phase 4 reduces time taken to reach threshold potential so increases rate
Effect of threshold potential becoming less negative, or increased hyperpolarisation (so membrane potential more negative) on cardiac action potential pacemaker rate
Slows pacemaker rate as longer time taken to reach threshold potential
Axon classification
Goldman-Hodgkin-Katz equation use
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
Communication between neurones
Secrete communication transmitter chemicals across synapse
Axoplasmic flow
Neurotransmitters are synthesised in the cell body and transported down axon to synaptic ends
