SDL: Action Potential Flashcards
the resting membrane potential
-70 mV
the phases of the action potential
rising phase, overshoot, peak, falling phase, after hyperpolarization
the ionic concentrations of a neuron are set up such that Na+ ions..
would be driven INTO the neuron along both its electrical and conc. gradients (if there are sufficient channels)
the large increase in permeability of Na+ allows for
a large Na+ inward current (depolarization)
the equilibrium potential for Na+
+60 mV (membrane potential approaches this but does not reach it)
what happens to ion channels at the threshold potential?
some voltage-gated Na+ selective channels open, increasing the permeability of the membrane to Na+
the 2 gates that Na+ channels have
activation/deactivation gate + inactivation/deinactivation fate
when the membrane potential is +, the electrical and the concentration gradients for K+ drive K+..
OUT of the cell
the resulting efflux of K+ causes which phase?
falling (repolarization), but it overshoots, causing the after hyperpolarization
effects of tetrodotoxin
blocks voltage-gated Na+ channels
effects of tetraethylammonium ions
block voltage-gated K+ channels
since potentials die out within a few millimeters, longer distance transmission of action potentials requires..
a system that regenerates the action potential along the axon
what causes eddy currents?
at threshold, voltage-gated Na+ channels open and Na+ rushes in, causing eddy currents from outside to the inside of the membrane; these evoke more eddy currents and propagate the AP
what is saltatory conduction?
when the AP skips from node to node on myelinated axons
myelinated fibers sequester voltage-gated K+ channels, so how does repolarization of the action potential occur? what does this prevent? Why is this important?
LEAKAGE of K+ channels that are not actively opened; this produces no-hyperpolarization, so the AP can be conducted at a faster rate
what happens to the voltage gated channels in demyelinating diseases like MS?
slow conduction occurs, and the voltage gated channels may be incorrectly distributed, so there is insufficient mechanisms to conduct an AP
what is the absolute refractory period?
during the spike part of the AP, the membrane cannot initiate another AP
what is the relative refractory period?
during the early part of the after-depolarization part, another AP can be initiated if stimulus is increased in strength
what is the subnormal period?
the after hyperpolarization phase: K+ channels still open and membrane potential is near equilibrium for K+, but another AP can be elicited by a stimulus if it is large enough to shift the MP to threshold. (Na+ channels will already be reset)
what is orthodromic conduction?
normal conduction direction from the AP, away from the soma
what is antidromic conduction?
conduction of AP toward the soma
what is an electrotonic/graded potential?
changes in cytoplasmic membrane potential, but not sufficient to propagate an action potential
what are examples of the normally occurring electrotonic potentials?
the excitatory and inhibitory synaptic ones and those at all sensory receptors
how can neuropathy be tested for?
fibers in a nerve can be stimulated by an electrical pulse to a cathode placed near a nerve (no flow of ions across the membrane).
if a cathode (neg pole) is placed near a near fiber, and there is an applied stimulus, the nerve fiber adjacent to the cathode will be..
depolarized
if the anode (pos pole) is used, the membrane will be..
hyperpolarized
example of mechanical pressure changing ions across the membrane
striking the “funny bone”
neuropathy is caused by
unhealthy nerve fiber with slowed conduction velocity
what is depolarization block? what causes it?
when the membrane potential remains above the threshold- can’t be repolarized; hypoxia or anoxia
amount of time the soma of a neuron can tolerate anoxia before the cell is killed
4 minutes
describe what is happening when limbs “go to sleep”
nerve fibers depolarize due to lack of energy to maintain membrane potential; when the MP does repolarize, numerous APs are initiated
what is hyperpolarization block?
when the MP is maintained below the resting potential level
drugs/events that cause hyperpolarization block
novocaine, lidocaine, hypoxia
what do local anesthetics block?
voltage-gated Na+ channels
what happens in an injury current?
severed nerve allows electrical currents to flow across a gap in the membrane for a short time
increasing the extracellular conc of K+ by a factor of 5x will cause..
depolarization (influx of Na+)
graded potentials dissipate..
within a few mms
local anesthetics block..
voltage-gated sodium channels
propagation of APs is necessary for the AP to travel over a few mms because
the resistance of axoplasm to the flow of ions is very high
demyelination of peripheral nerve fibers causes APs to have..
a decreased conduction velocity
