action potentials Flashcards
depolarization
membrane potential becomes less negativw
hyperpolarization
becomes more negative
what does the direction of change in potential depend on
direction of movement of the ion - into = influx, out = efflux
charge carried by ion
what does movement of ions across membranes requirw
ion channels
what is passive movement of an ion through an ion channel dirven by
electrochemical gradient for that ion
movement of na+ in response to the opening of sodium sleective channels
na+ flows inwardly generating an inward current
why does the na+ produce an inward current
the concentration gradient is inward
electrical gradient is inward
membrane potential of many neurones
-70mv
equilibrium potential for na+
+60mv
driving force for na influx
vm- ena
movement of k+ in response to opening o k+ channels
k+ flows ourwardly generating an outward current
why does k+ geenrate an outward current
conc gradient is outwards and has an energy which exceeds that of the electrical gradient which is inward
equilibrium potential for k+
-90mv
driving force for k+ efflux
vm - ek
effect of opening na+/k+ channels upon membrane potential
membrane potential driven towards whichever channel is openign
ion channel
protein complexes spanning lipid bilayer forming a central pathway that permits rapid flow of selected ions
types of ion channels
voltage gated- membrane voltage
ligand gated- chemical substances
mechanical/ thermal- physical stimuli
ion channel responsible for na+ channels
voltage activated na+ channels- depolarizing
ion channel responsible for k+
voltage activated k+ channels - hyperpolarizing
when are action potentials generated
when threshold is reached, all or none
self reinforcing na+ channels meaning
the opening of a few channels causes further depolarisation; positibe feedback
self limitting k+ channels
outward movement of k+ causes repolarization which turns off the stimulus for opening; negative feedback
refractory period
na+ channels enter a non conducting, inactivated state during maintained depolarization
what is repolarization required for
the channel to enter the closed state
absolute refractory period
no stimulus, however strong, can elicit a second action potential ; all na+ channels inactivated
relative refractory period
stronger than normal stimulus may eleicit a second action potential; mixed population of inactivated and closed channels, membrane is hyperpolarized
role of dendrites
recieves incoming signals and passes to soma
role of axon
conduct action potentials over long distances
role of axon terminal
releases neurotransmitter to other cells
strategies to increase passive current spread
increase axon diameter
decraese leak of current across the axon; add myelin by schwann cells in PNS and ooligodendrocytes in CNS
types of macroglia
schwann cells and oligodendrocytes
saltatory conduction
jumping between nodes of ranvier
what do preganglionic parasympathetic nerves agonise
nicotinic ach receptors of post ganglionic neuroneswha
what do post ganglionic parasympatetic nerves agonise
muscarinic ach receptors
which body fluid compartment contains largest volume of fluid
intracellular
