Membrane Electrophys: Action Potentials Flashcards
Define action potential.
rapid change in membrane potential away from the normal, negative resting voltage to a positive voltage (followed by return back to negative potential)
What allows nerve and muscles to have excitability?
have specialized function allowing ability to deviate membrane potential from RMP through altering permeability of key ions
what is polarization?
positive or negative charge of membrane (what it sits at) other than OmV
what happens when membrane potential becomes less polar (less negative) than resting?
hypopolarization
what happens when membrane loses negative polarity or RMP (become less negative-0-positive)?
depolarization
what is it called when the membrane returns to RMP after depolarization?
repolarization
what is it called when the membrane become more polarized that RMP (even more negative)?
hyperpolarization
what is threshold?
potential where, when hypopolarized membrane potential reaches it, causes sudden increased of Na+ into the cell and depolarization
what voltage gates open and close quickly?
Na+
what voltage gates open and close slowly?
K+
what does the flow of Na+ ions into the cell do?
reverses the membrane potential and drives it to the Na equilibrium potential (depolarization)
what does the flow of K+ out of the cell do?
restores the membrane potential to resting (depolarization)
what are the stages of depolarization?
- initial depolarization
- Na+ channels open
- Na+ influx
- Peak Na+ conductance
what are the stages of depolarization?
- early depolarization
- K+ efflux
- peak K+ conductance
what helps to reestablish the RMP?
Na+/K+ pump - gradually helps restore original resting ion distribution
why can numerous APs occur even in absence of Na+K+ pump keeping pace?
because only a small fraction of ions contribute to AP (1 of 100,00 K+ ions exit the cell during AP)
time period after AP when a subsequent AP either cannot or likely will not be generated?
refractory period
what is the point of a refractory period?
ensure unidirectional propagation of APs
period when no AP regardless of stimulus intensity can occur due to “locking” of Na+ channels.
absolute refractory period
period when AP can only be produced if the stimulus is large enough due to hyperpoloarization of the membrane potential?
relative refractory period
what are the two factors that cause presence of refractory period?
- inactivation of Na+ channels
- membrane hyperpolarization
what the main characteristics of action potentials?
- undiminished propagation/”regeneration” of AP along the plasma membrane
- “all-or-none” law: AP is either generated or not, same size every time
local sub-threshold changes in membrane potential?
graded potentials
what are the main characteristics of graded potentials?
- sub-threshold
- duration and strength directly proportional to duration and strength of stimulus
- decremental
- can be summated
what will happen to a graded potential if it reaches threshold?
will become an action potential.
what part of the neuron has the lowest threshold for AP initiation?
axon hillock (initial segment)
what are the two ways a signal can be conducted down the axon?
- contiguous - locally propagated down each adjacent portion of the membrane
- saltatory - ‘jumping’ along nodes of ranvier (holes in myelinated axon)
what two things increase conduction down an axon?
- large axon diameter
- myelination
what does myelin do?
- forces current to travel node to node where there is lower resistance
- minimizes loss of current across otherwise leaky membrane
what is the specialized junction between the opposing membranes of two excitable cells?
synapse
what are the 2 categories of synaptic communication
electrical synapses
chemical synapses
what is used to carry a signal across synapses to postsynaptic receptors in chemical synapse?
neurotransmitters
influence of thousand of presynaptic cells on a single cell?
convergence
influence of one presynaptic cell on many cells via branching axon terminals
divergance
what are the two kinds of ‘signals’ a cell can receive?
excitatory synapse - always excitatory, depolarizes/hypopolarizes membrane (EPSP)
inhibitory synapse - always inhibitory, hyperpolarizes the membrane (IPSP
how can graded potentials summate from dendrites to generate AP at axon?
- temporal summation: arrive at rapid enough frequency to be summed and reach threshold
- spatial summation: from multiple inputs combine and are summed to reach threshold
- cancellation: EPSP and IPSP combine to cancel each other –> no AP
