2.3: Membrane potential and action potentials Flashcards
What is the Nernest equation used to calculate?
Equilibrium potential
What does the Goldman-Hodgkin-Katz equation calculate?
The membrane potential of the cell if the following is known:
Concentration of ion in cell
Concentration of ion outside of the cell
Permeability of membrane to that ion at any one point to those concentrations
Describe the steps of action potential generation
1)Resting membrane potential
2)Stimulus depolarises membrane, moves in positive direction towards threshold
3)Upstroke- VGSC open quickly so Na+ enters cell down electrochemical gradient. VGPC open slowly so K+ leaves cell down gradient - membrane potential moves toward Na+ equilibrium potential
4)Repolarisation - decreased permeability of Na+ and VGSC close. Increased permeability of K+ as VGPC stay open so K+ leaves cell down its electrochemical gradient
Membrane potential moves towards K+ equilibrium potential
5) K+ continues to leave as VGPC still open, until conc. gradient moves towards equilibrium -
Some VGPC then close, membrane potential returns to resting potential
What is the absolute refractory period
Period where inactivation gate of VGSC is closed and so a new action potential cannot be triggered
What is the relative refractory period?
Period of time where you need a stronger than normal stimulus to trigger another action potential
Due to hyperpolarisation, more of a depolarisation is required to reach threshold and then cause another action potential
How is an action potential an example of positive feedback?
Once the depolarisation occurs so that it is above the threshold potential, VGSC open
Increasing permeability which causes an influx of Na+
This causes more depolarisation repeating the cycle of opening VGSC to increase Na+
APs are generated as a result of
all or nothing event
Saltatory conduction
Myelin prevents AP spreading because it has high resistance and low capacitance
- AP jumps between nodes of Ranvier
- unable to jump across gap at axon terminal
What factors affect conduction velocity
larger diameter = faster conduction
myelination = faster conduction
other factors can also affect conduction -
cold, anoxia, compression, drugs
Ion movement during AP
-ion PUMPS not directly involved in ion movement of AP
- ion TRANSPORTERS restore ion concentration gradients
Propagation of action potentials
Passive propagation results from local change in ionic conductance that spreads along a stretch of membrane - becoming exponentially smaller
Neurotransmission across synapses
1) propagation of action potential (AP)
2) Neurotransmitter release from vesicles
3) Activation of postsynaptic receptors
4) Neurotransmitter reuptake
process of action potential propagation
AP propagated by VGSC opening
Na+ influx -> membrane depolarisation ->AP moves along
VGKC open > K+ efflux -> repolarisation
process of neurotransmitter release from vesicles
AP opens voltge-gated CA2+ channels at presynaptic terminal
Ca2+ influx -> vesicle exocytosis
process of activation of postsynaptic receptors
NT binds to receptors on PSmembrane
Receptors modulate post-synaptic activity
