mem and action potentials Flashcards
what is resting mem potential (Vm)
electrical potential difference across the mem
t/f there are no exchange of ions when the meme is at rest
false, there are no massive exchanges but there are still a little so the mem can stay at rest
where are Na+ and K+ most prominent at rest
there is more Na+ outside the cell at rest and theres more K+ inside at rest
what would happen if the mem was only permeable to K+
K+ would diffuse down its concentration gradient until the electrical pot across the mem counters the K+ diffusion
if the mem was only permeable to K+ when would the mvt of K+ stop
when the [ ] diff would = electrical difference
what is the electrical pot that counters net diffusion of K+ called
K+ equilibrium (Ek) or the Nernst pot for K+
what is called the electrical pot across a mem that exactly opposes the net diffusion of a particular ion thru the mem
the Nernst potential or the equilibrium potential
how is the Nernst pot determined
by calculating the ratio of the [ ] of that particular ion on the 2 sides of the mem
what is the Nernst equation
EMF = ± 61 log ( [inside] / [outside] )
what is the EMF
electromotive force that drives ions from inside to outside the cell and vis versa
how is the sign determined in the Nernst equation
if the ion is positive than the sign of the equation is negative
what would happen if the mem was only permeable to Na+
Na+ would diffuse down its [ ] gradient until a pot across the mem counter the Na+ diffusion which will stop the Na+ mvt
what does the permeability depend on
-concentration of respective ions on the inside and outside of the mem
-permeability of the mem to each ion
-polarity of the electrical charge of ions positive or negative
why is Vm so much closer to the Nernst pot of K+ than to it of Na+
because the mem is far more permeable to K+
what are the transport methods and their properties of resting n. mem
Leak channels; much more permeable to K+ than Na+
and Na+/K+ pump; net increase of 1 positive charge outside (more negativity inside)
what is the resting mem pot for large n. fibers (motor neurons) and for small neurons (interneurons) of nervous sys
large n. fibers: -90mV
small neurons of nervous sys: -70mV
what are the 3 factors that the resting mem pot depend on
-diffusion of K+ & Na+ ions : K+ (inside to outside) and Na+ (outside to inside)
-permeability of ions thru leak channels: P to K+»_space; P to Na+ (about 100 times more)
-Na+/K+ pump: creates more negativity inside (3 Na+ go outside and 2 K+ go inside)
t/f the resting mem pot is closer to the equilibrium pot for the ion w the lowest permeability
w the highest permeability
what are some synonyms of a.p
spike, impulse or firing
what is the name for a very rapid change in the mem pot from - to + values and return back to initial resting pot level
action potential
t/f if the impulse is higher the amplitude of the ap with be higher as well
false, an ap is an all-or-none event, either it occurs fully or it doesn’t occur at all (amplitude of an ap never changes)
what is the path of an ap
it moves along the nerve fiber until it comes to the end of the fiber
what are the functions of an ap
-transmitting n. signals
-rapid transmission over distance
-encoding info (neuronal language)
from where to where does the ap transfer sensory info
transfers from pns to cns
from where to where does the ap transfer motor info
transfers from cns to pns
can the ap also transfer info from one part of the cns to another part of the cns
yes
speed of transmission (conduction velocity) of ap depends on what
fiber size and whether it is myelinated
which ap will travel faster btw proprioception, ankle injury and a pressure on the skin
proprioception is fastest, pressure on skin and ankle injury is the last to be felt
what can vary in an ap depending on the type of pressure applied to the skin
the frequency of the ap; a stronger stimulus will cause a higher frequency of ap
what is the resting state of the n. action pot
-90mV
what is the depolarization (how fast is it and what causes it)
- -90 to 35 mV
-0.1 ms period (very rapid)
-caused by the sudden opening of the Na+ channels, Na+ ions flow to inside the cell
what is repolarization (what closes and what opens, what results after)
-Na+ channels begin to close, Na+ ions stop flowing inside
-K+ channels open slowly; K+ ions start to flow inside
this re-establishes the negativity of the resting mem pot
what is the afterpotential (what causes it)
-less than -90 mV
-caused by K+ channels that remain open for a few milliseconds after repolarization of the mem is completed
-excess K+ flows out of the mem
what is the back to resting stage (what causes it)
the closing of the K+ channels
different stages of the ap are due to the activation of what protein channels on the n. mem
voltage-gated Na+ channels
voltage-gated K+ channels
the voltage gated channels are sensitive to what and are considered what kind of diffusion
changes in mem electrical pot
simple diffusion (electrical gradient is used so no need for E)
where are the 2 gates situated on the Na+ channels
the activation gate is on the exterior side of the mem
the inactivation gate is on the interior side of the mem
what are the states of the gates at resting state
activation gate is closed and inactivation gate is open
no entering of Na+ ions
what are the states of the gates at activated state (depolarization); what causes it and what flows in or out
-activation gate and inactivation gate are both open
-sudden opening of the activation gate is due to shifting of the mem pot towards positive values
-sodium ions flow inside
what are the states of the gates at inactivated state (repolarization); when is the gate activated, what stops flowing in/out
activation gate is open and inactivation gate is closed
inactivation gate is activated when mem pot increases above 0mV
Na+ ions stop to flow inside and the mem pot recovers back to resting state
what is the opening threshold for the Gated sodium channels and what happens to the permeability to Na+
-70 to -50 mV
permeability to Na+ increases to 500 to 5000 times more than at rest
when can the inactivation gate reopen after repolarization
only when the mem returns to resting potential
where is the gate situated in a gated K+ channel
interior side of mem
what are the 2 states of the gate in the K+ channel
resting state; gate is closed
slow activation state; gate is open
what happens in the slow activation state (repolarization); when are the K+ channels activated, what opens as the other closes, what flows out and what does it accelerates repolarization towards
they are activated when the meme pot increases above 0mV
gates open slowly at the same time as the Na+ channels begin to close
K+ ions flow outside
it accelerates repolarization towards resting pot
what happens during undershoot ; what channels are open, what excess of ions flow out of the cell
K+ channels remian open for a few milliseconds after repolarization of mem is completed
excess K+ ions flow outside of cell
what gate closes at back to resting state
K+ gate closes & mem pot comes back to -90mV
what is the threshold for initiation
level of mem pot at which the positive feedback cycle is created (point of no return)
when does the threshold occur
when the nb of Na+ ions entering the nerve becomes greater than the number of K+ ions leaving the n.
what is the threshold for a nerve with a Vm of -90mV
about -65mV
what causes the initial increase in mem pot that reaches the threshold
electrical stimulation (tingling feeling in physio tx)
mechanical stimulation (poked by a needle)
chemical stimulation (neurotransmitters)
the amplitude of an AP is ___ of the ___ of the stimulus that evokes it
independant
intensity
the frequency of firing is ___ on the intensity of the stimulus
dependant
what is the period during which a new AP cannot occur as long as the mem is still depolarized from the preceding ap
absolute refractory period
why can’t a new ap be generated during the absolute refractory period
bc
-Na+ channels are inactivated
- mem has to return near original resting pot to allow inactivation gates to open (can’t restimulate a neuron thats already there)
what is the period that follows the absolute refractory period during which a new ap can occur in response to a stronger stimulus than normal
relative refractory period
why can an ap only be generated with a stronger stimulus than normal during the relative refractory period
bc
-some Na+ channels start to go back to resting state and others are still inactivated (wont have the same nb of Na+ ions to start with)
-K+ channels are still open and the mem is hypolarized (during the undershoot bc K+ ions are still leaving the cell)
myelin is an extension of what particular cells
glial cells
what are glial cells called in the cns and in the pns
pns: schwann cells
cns: oligodendrocytes
what is myelin sheat
fatty white substance that surrounds the axon and thus isolating n. fibers bc ions can’t flow significantly through thick myelin
what interrups the myelin sheat every 1 to 3 mm
nodes of Ranvier
where can the exchange of ions occur (ap generated) on a myelinated axon
only at the level of nodes of Ranvier (where the voltage gated channels are located), and ap are conducted from node to node
what is saltatory conduction (what does it do concerning E and what is the conduction velocity)
it conserves energy for axon (little metabolism required to re-establish ionic [ ] differences)
conduction velocity varies from as little as 0.25 m/s in unmyelinated fibers to as great as 120 m/s in large myelinated fibers
how does the propagation of ap work in unmyelinated n. fibers (what makes the adjacent portions of the mem reach the threshold and what is the conduction velocity)
ap excites adjacent portions of mem resulting in propagation of the ap
when Na+ ions flow to adjacent area; they increase voltage of adjacent area to the threshold level which initiates adjacent ap
conduction velocity is 0.25m/s
what is MS
immune-mediated inflammatory disease that causes the demyelination of the cns resulting in m. weakness, loss of sensation and death
how does the all or nothing principle apply to MS
if conditions arent right; it will stop altogether ap propagation
