Action potential Flashcards
What affects permeability of the membrane?
Conformational state of ion channels
Opened by depolarisation, but inactivated by sustained depolarisation.
What is the resting membrane potential due to (what makes it that value)
Potassium efflux from the cell
Not due to Na+/K+ ATPase
What happens when there is a stimulus?
Depolarisation of the membrane potential to a more positive value
What is the threshold value of the membrane potential?
What happens here
-55mV
Most voltage gated sodium channels respond to change and open
What happens in depolarisation of membrane potential?
Permeability to sodium increases significantly (due to VGCSs open so Na+ influx down electrochemical gradient)
Pk also slightly increases as K+ channels also open slowly so K can gradually leave the cell
Membrane pot slowly move towards Na+ equilibrium potential
What happens in repolarisation of the membrane potential?
Na+ channels inactive as pore blocked by channel protein, so permeability Na decrease and more K+ channels open and stay open so Pk increase and electrochemical gradient efflux. Membrane pot reach K+ equilibrium potential
What happens after hyperpolarisation of membrane potential?
VGKCs open at rest, so K+ continues to leave cell. Causes movement towards K+ equilibrium potential, closing slowly. Relative refractory period
What happens in early repolarisation?
Inactivation fate closed in absolute refractory period. New action potential cannot be triggered even with very strong stimulus, despite activation gate remaining open. Causes more potassium channels to open
What happens in late repolarisation?
Both activation and inactivation gate are closed
What happens in absolute refractory period?
Inactivation gate is closed
New action potential canot be triggered even with a strong stimulus.
Occurs after depolarisation automatically, arresting move to Na+ equilibrium potential
What happens in relative refractory period?
Inactivation gate open, stronger than normal stimulus required to trigger an action potential. Needed because cell is hyperpolarised so larger change in potential needed to reach threshold potential
What happens in passive propagation?
Only resting K+ channels open
What happens in active propagation?
Used for action potentials. Local currents depolarise adjacent area of the axon. Previous section refractory so cannot go backwards
What increases the speed of propagation of action potentials?
Increasing diameter
Myelination
What slows the speed of propagation of action potential?
Cold Anoxia Compression Drugs Lack of myelination Reduced axon diameter
