Nervous system: Membrane potential Flashcards
voltage of extracellular fluid
0
membrane potential
-70mV
relative to outside
distribution of ions across plasma membrane
most Na+ outside. most Cl- outside
most K+ inside
small conc of Cl- inside leads to overall negative charge inside cell
2 factors affecting magnitude of resting potential
differences in specific ion concentrations
differences in membrane permeability for different ions
why is the equilibrium potential closer to K+ for the resting potential of membrane
K+ has very high permeability (many potassium channels)
graded potentials
signalling over short distances
changes in membrane potential that are
confined to a relatively small regionof the plasma membrane.
magnitude of the potential can vary
can depolarise or hyperpolarise
no threshold or refractory period
action potentials
long distance signals
large alteration in membrane potential
all or nothing response
very rapid
excitability
amplitude is fixed
hyperpolarisation
membrane more negative than resting
how graded potentials work
chemical stimulus opens channels and positive ions flow in
membrane potential less negative than adjacent areas
Different stimulus intensities result in
different degrees of
depolarisation.
why do electrical currents die out with graded potentials
membrane leaky/permeable to ions (decremental)
further from site of depolarisation you go, charge decreases
solved with summation
ligand gated and mechanically gated channels
serve as initial stimulus for action potential
voltage gated channels
allow rapid depolarisation and repolarisation
what is responsible for the conformational change to channels when there is a change in membrane potential
charged amino acid residues
why are voltage gated sodium ion channels faster to respond
have inactivation gates
makes it faster
action potential mechanism
- Resting membrane potential close to K+
equilibrium as normal K+ channels are “leaky” - Action potential begins when a stimulus
(e.g., a chemical neurotransmitter) binds to a
specific ion channel, allowing Na+ to enter - Other Na+ channels stimulated to open by
the depolarisation: positive feedback - Na+ channels become inactivated and K+
channels now open with a delayed effect
halting depolarisation - K
+ fluxes out of the cell rapidly repolarising
the membrane - The return of resting membrane potential
closes Na+ channels, but the sluggish K+
results in hyperpolarisation - As K+ channels close, resting membrane
potential returns
threshold potential
15mV above resting potential
subthreshold potentials
weak polarisations
caused by subthreshold stimuli
absolute refractory period
during an AT, another stimulus will not cause another AT
occurs during the period when the voltage-gated Na+ channels are either already open or have proceeded to the inactivated state during the first action potential.
relative refractory period
interval following absolute refractory period during which a second action potential can be produced—but only if the stimulus strength is considerably greater than usual. starts as the voltage-gated sodium (Na⁺) channels begin to reset and continues until the neuron returns to its resting membrane potential.
refractory periods, general
limit the number of
action potentials an excitable
membrane can produce in a given
period of time.
action potential propagation
process of AT travelling along length of neurone
there is a sequential opening and closing of voltage-gated Na+ and K+ channels along the membrane
why dont action potentials decrease in magnitude along length like graded potentials
each regeneration of the action potential depends on the positive feedback cycle of a new group of Na+ channels where the action potential is occurring, the action potential arriving at the end of the membrane is virtually identical in form to the initial one
