Trans - Neuronal Excitability II Flashcards
transient shift of membrane potential in a localized cell area
local potential
characteristics of local potential
- localized
- graded
- decrementally transmitted
- may be summated
- very rapid
[T/F] local potential is faster than AP
T
types of local potential
- synaptic - IPSP or EPSP
- generator potential - sensory organs
- electronic potential - associated with AP
potential that occurs in sensory organs
generator potential
local potential that occurs along the axon as the action potential travels along it
electronic potential
time required for a membrane potential to change after a stimulus is applied
time constant
high resistance - ______ time constant
greater
high capacitance - _______ time constant
greater
ability to store charges of opposite signs on two opposing surfaces
capacitance
less leakage of ions across the membrane means that local potential will _________
travel farther from the source
distance at which the initial transmembrane volume change has fallen to 37% of its peak value
space constant
relationship of space constant to transmembrane resistance
directly related
relationship of space constant and internal axoplasmic resistance
inversely related
the larger the space constant, the ______ along the membrane a voltage change is observed after a stimulus is applied
farther
transmembrane resistance
how well a membrane blocks ions from leaving
the higher the transmembrane resistance, the _____ the space constant
higher
internal axoplasmic resistance
resistance to ion flow within the axon
how does internal axoplasmic resistance affect space constant
when the resistance is high, ions cannot mvove away from the source quickly –> lesser space constant
action potential - define
fleeting, self-renewing wave of depolarization (positive wave) that propagates without decrement along the entire length of the nerve axon at high speed
orthodromic conduction
conduction in one direction ( in axon away from soma)
antidromic conduction
conduction from axon toward soma
conformations of Na gate, and components
- resting - activation gate closed, inactivation gate open
- open - activation gate open, inactivation gate open
- inactive - activation gate open, inactivation gate closed
effect of reaching threshold potential
opening of Na and K gates, action potential starts
spike potential
rapid rise and fall of membrane potential due to fast sodium gates
absolute refractory period - define
no new AP is produced no matter how strong the stimuli
absolute refractory period - mechanism
all Na gates are already open, no new change in Na gradient can be created
relative refractory period - define
stronger than normal stimulus can cause AP
relative refractory period - mechanism
some Na channels are closed again - may be reopened to generate new AP
prevents AP from reversing direction
relative refractory period
supranormal refractory period - define
easier to reach threshold and create AP because the electrical charge inside the membrane is nearer the threshold
supranormal refractory period - mechanism
continued efflux of K due to slow K channels - causes membrane potential to be relatively more negative
subnormal period
overshooting of membrane repolarization due to slow K gates
subnormal period is corrected by:
Na-K pump
AP has constant ____ and _______
amplitude and form
an increase in the axon diameter will (1)_______ the space constant, (2)_______ the time constant, and (3)_______ the conduction speed
- increase
- decrease
- increase
myelinated axon conduction velocity
3-120 m/sec
unmyelinated axon conduction velocity
0.5-2 m/sec
presence of myelin leads to (1)_______ in effective resistance of axonal membrane. why?
- increase, because ions must flow through myelin before reaching ECF
presence of myelin leads to (1)________ in effective capacitance. why?
- decrease, because of the greater distance between ECF and ICF
saltatory conduction
electrical signal jumping from one node of ranvier to the next
