graded potentials and action potentials Flashcards
what are graded potentials
transient electric signals that travel short distances
what are action potentials
self-replicating transient electrical signals that travel long distances
are graded potentials depolarizing or hyperpolarizing?
can be either
characteristics of graded potentials
- vary in amplitude and duration - produced by chemical, physical, or electrical stimuli - exhibit decremental conduction
what is decremental conduction
the more frequently the nerve is stimulated, the slower it conducts
how do graded potentials propagate
local current flow
how does the excitatory post-synaptic potential work?
- neurotransmitter binds to receptor
- activates ion channel permeable to sodium
- results in depolarization of the post-synaptic membrane
give two neurotransmitter examples that are used to initiate a excitatory post-synaptic potential
- glutamate
- acetylcholine
explain how a inhibitory post-synaptic potential works
- neurotransmitter binds to receptor
- opens potassium or chloride channels
- hyperpolarizes the cell
give 2 examples of neurotransmitters that initiate a inhibitory post-synaptic potential
- GABA
- Glycine
how long do chemically gated ion channels generally stay open
stay open as long as the neurotransmitter is bound to the receptor
is there a change in intracellular concentrations of ions during graded potentials
no significant change
what effects the amplitude of the graded potential
amplitude varies with magnitude or strength of specific stimulus
what happens to the magnitude of the graded potential as it leaves the site of origin
maginitude decreases
where does integration of graded potentials occur
cell body
where is the site of axon potential generation
axon hillock
what is temporal summation
synaptic potentials produced by the SAME pre-synaptic neuron on the same post-synaptic cell overlap in time
- postsynaptic potentials overlap and add to one another
- thus, if the first potential hasn’t completely decayed before the second one arrives, it will add on to the first one
what is spatial summation
synaptic potentials produced by DIFFERENT pre-synaptic neurons on the same post-synaptic cell
- individual postsynaptic potentials add together in space
- effect of multiple inputs in additive
what is the purpose of dendrites
conduct graded potentials to the cell body
What is the potential that is a self-replicating transient electrical signal that travels long distances
action potential
what is the potential that is a transient electric signal that travels short distances
graded potential
give some characteristics of action potentials
- stereotypical size and shape
- all-or-none phenomenon
- non-decremental propagation
what is the all-or-none property of action potentials?
- once action potential is fired, the amplitude remains constant and independent of stimulus above this threshold
- an action potential occurs in total or it does not occur at all
an action potential results from transient changes in the what to certain ions
permeability of membrane (concentrations do not change)
what controls depolarization
voltage-gated “fast” sodium channels
- Na+ channels are closed at rest
- channel opens very rapidly when Vm depolarizes by a certain amount (threshold)
- channels quickly inactivate - NOT involved in resting Vm
Describe what is going on in repolarization
- voltage-gated Na+ channels inactivate
- voltage-gated K+ channels open
What is the absolute refractory period
interval during which NO stimulus can elicit an action potential
- inactivation gates, once closed, remain closed until membrane is repolarized
what is the relative refractory period
interval when a supernormal stimulus is required to elicit an action potential
- due to elevated gk coupled with the residual inactivation of sodium channels
what is the relationship between conduction velocity and fiber diameter
conductional velocity is proportional to fiber diameter
myelinated axons prevent current flow where
across the surface of the membrane
where do action potentials occur on the axon
occur at the nodes of ranvier
segments of axons covered by myelin have many or few voltage gated Na+ channels
few
nodes contain high or low concentrations of voltage gated Na+ channels
high! action potentials occur at the nodes
saltatory conduction
leaping of action potential from node to node
how can you distinguish the level of stimuli
via the frequency of action potentials
- a single action potential cannot convey information about the magnitude of the stimulus that initiated it
stimulus strength affects amplitude in graded or action potentials
graded response: amplitude varies with stimulus intensity
which, graded or action potentials, have decremental conduction
graded potential
which, graded or action potential, has a refractory period
action potential
