Graded and Action Potentials Flashcards
what is neural communication?
based on rapid changes in membrane permeability to ion
why do you use ion permeability changes and not 2nd messenger systems or hormones for cell-to-cell signaling in the brain?
because the change in membrane potential is VERY fast –> a lot faster than hormone signaling
what ion channels are involved in gated and action potentials?
ligand-gated and voltage-gated channels
what does depolarization cause?
decrease in potential –> membrane becomes less negative
what does repolarization cause?
return to resting potential after depolarization
what does hyperpolarization cause?
increase in potential –> membrane becomes more negative
what do graded potentials depend on?
the permeability changes induced by the neurotransmitter in the postsynaptic neuron
what is EPSP?
excitatory postsynaptic potentials —> makes the membrane less negative
what is IPSP?
inhibitory postsynaptic potentials –> makes the membrane become more negative
how many postsynaptic potentials are needed to create an action potential?
if threshold is reached, then it creates an action potential
ie: depends on how many it takes to reach the threshold
what is a typical EPSP voltage and how long does it last?
0.5 mV
20 ms
what is temporal summation?
occurs when single synapse receives many EPSPs in a short period of time
what is spatial summation?
occurs when single synapse receives many EPSPs from many presynaptic cells
what is action potential and how does it propagate?
one-way propagation/all or none contraction
signal propagates non-decrementally –> the impulse propagates along an axon (the amplitude of the impulse is maintained as it progresses)
what type of gates do voltage-gated Na+ channels have?
activation gate AND inactivation gate
what type of gates do voltage-gated K+ channels have?
ONLY HAS ONE GATE that can be open or closed
describe the resting potential conformation of voltage-gated sodium channels
closed but is capable of opening
at resting potential –> -70 mV
describe the activated conformation of voltage-gated sodium channels
open (activated)
from threshold to peak potential (-50 mV to +30 mV)
describe the inactivated conformation of voltage-gated sodium channels
closed and not capable of opening (inactivated)
from peak to resting potential (+30 mV to -70 mV)
describe the resting conformation of voltage-gated K+ channels
closed
at resting potential, delayed opening triggered at threshold
remains closed to peak potential (-70 mV to +30mV)
describe activated conformation of voltage-gated potassium channels
open
from peak potential through after hyperpolarization phase (+30 mV to -80 mV)
what is the absolute refractory period?
interval during which no stimulus can elicit an action potential
most voltage-gated Na+ channels are inactivated
what is the relative refractory period?
interval when a supranormal stimulus is required to elicit an action potential
due to elevated gK coupled with the residual inactivation of voltage-gated Na+ channels
why is there a refractory period?
ensures a one-way propagation of the action potential
limits the frequency of action potentials (energy conservation; prevent seizures)
what determines the speed of conduction?
diameter of the fiber: the larger the diameter of the fiber, the lower the internal resistance for current flow and the faster it conducts
-rapid fibers: motorneurons
-slow fibers: internal organs
myelination: lipid insulator of nerve fibers that greatly increases the conduction velocity by decreasing the capacitance of the axon and restricting the AP generation to the nodes of ranvier
what is contiguous conduction?
conduction in unmyelinated fibers
AP spreads along every portion of the membrane
