membrane potentials and action potentials Flashcards
the potential difference of 94 millivolts inside is when?
when there is high concentration of potassium ions inside than outside and the membrane is only permeable to K ions this creates a gradient which allows the K ions to move towards the outside. this process causes a DIFFSUION POTENTIAL and a negative potential difference in the inside of the cell
the potential difference is 61 millivolts in the inside when?
when NA is higher in concentration in outside than inside and the membrane is only permeable to NA ions, this causes the movement of Na ions to the inside making the inside positive and creation a potential difference of 61 millivolts
when membrane is permeable to more ions the diffusion potential depends on?
- POLARITY of electric charge of each ions
- the concentration of each ions to the inside and outside
- the permeability of membrane to each ion
what is Goldman equation
gives calculated membrane potential on the inside of membrane when two univalent +ve ions are present (na and K) and one univalent -ve ion is present (cl)
what several key points become evident from Goldman equation?
- Na, K, cl ions are the most important ions involved in the development of membrane potential
- the quantitative importance of each of these ions in measuring membrane potential is equal to their permeability across the membrane
- positive ion concentration gradient from inside to outside will cause the inside to be electronegative and vice versa when there is negative ion concentration
- permeability of K and Na ions change but Cl doesnt
change throughout of nerve impulse transmission
how measuring of membrane potential is done
micropipette is filled with electrolyte, it is then impaled inside the cell to the cell fiber. an electrode is connected to ecf called indifferent electrode and then the potential difference between the inside and outside is measured through a voltmeter, a microelectrode is attached to an oscillator for rapid measurement
resting membrane potential of large fibers when they are not transmitting impulse
it is -70 millivolts, which tells its more negative in the inside to the outside
gradient for Na outside and inside is
142 and 12 mEq/L
gradient for K outside and inside
4 and 140 mEq/L
if K ions were the only ions causing resting potential, the potential would be?
-94 millivolts
using goldman eq to measure the membrane potential caused by K and Na ions is?
-86 millivolts
net membrane potential is what and how?
its 90 millivolts total, diffusion of Na and K which creates the membrane potential of -86 millivolts nd then additional of -4 millivolts of Na/K pump
what is action potentail
the rapid change in the membrane potential that is spread rapidly along a nerve fiber membrane
resting stage of action potential
it is -70 millivolt. the membrane is said to be polarized in this stage.
depolarization of action potential?
the membrane sudden becomes permeable to Na ions causing their movement to interior of the axon which changes the membrane potential to somewhat positive. it shoots zero to the +ve side in large fibers
necessary factor for depolarization and repolarization
voltage gated Na channel and voltage gated K channel
when does activate sodium channel open
when the resting membrane from -70 drops to about -55 millivolts the gates open causing the movement of Na ions inward which increases as much as 500-5000fold
inactivation Na channel close
it closes in 10,000th of a second after the activation gate has been opened and it remains closed as long as membrane potential doesn’t return to normal.it causes repolarization
voltage gated potassium channel and its activation
it gets activated when the membrane potential increases from -70 to zero millivolts and cause the efflux of K ions the outside.
threshold for stimulation is?
-55 millivolts
all or nothing principal ?
when an action potential has been elicited at any point on the membrane, the depolarization spreads in the membrane in all directions if conditions are right, if NOT it doesn’t travel.
safety factor for propogatiom
the ratio of action potential to threshold for excitation must be greater than 1.
plateau in some action potentials is causes by what factors
fast opening sodium channels, slow sodium calcium channels and the slow K channels (VOLTAGED GATED) and takes place in cardiac muscles.
which drug causes a repititive discharge from cells like skeletal and large nerve fibers?
veratridine.
myelin sheath is deposited by what >
it is deposited by Schwann cells.
around axon there is multiple layer of what
Schwann cells membrane containing sphingomyelin lipid
node of ranvier?
the junction between each 2 successive Schwann cells which is 2-3 micrometers is where the ions can still flow with ease through axon
any factor that causes the Na ions to move inward sets off?
automatic regenerative opening of Na channels
what are the factors that can open the automatic regenerative Na channels?
any mechanical disturbance, chemical effects or passage of electricity
absolute refectory period?
the period during which a 2nd action potential cannot be elicited when when a strong stimulus is given.
what happens when equal number of positive ions from the outside to the inside what is the membrane potential?
it changes from -70 millivolts to +35 millivolts.
why the membrane potential is -86 inside the cell when measured by goldman equation
the cell is 100 times more permeable to K ions than Na ions so the diffusion of K contributes far more than Na to the membrane potential so that why its -86millivolts which is near to the potassium potential which is -94 millivolts.
how the full recovery of resting membrane potential occurs
the closure of na channels and the efflux of K ions outside the cell speed up the repolarization state.
when threshold potential is reached
it is reached when the number of Na ions diffusing inside of the cell are greater than the K ions diffusing outside.
how sodium and potassium ionic gradient is re established
it is re established by the Na/K pump which diffuses the Na ions from the inside back to the outside where they orignally were and the K ions back to inside. this is done thorugh ATP
special feauture of NA-k atp pump is?
degree of atcivity is strongly stimulated when the accumalation of Na ions is more inside.
the concentration of na increases from what to what causes the activity of pump increases what fold?
it increases from 10-20 mEq/L the activity increases 8 fold
the rhytimcal discharge causes
the rhythmical beating of the heart rhythmical peristalsis of intestines rhythmic breathing (neuronal events)
skeletal muscles or large nerve fibers discharge when placed in?
veratridine
why heart membrane does not depolarize immedetaile after it repolarizes
potassium conductance
hyperpolarizatiom
in the heart membrane at the end of action potential the membrane becomes more permeable to potassium casying K ion efflux for 1 sec even after the action potentoal is over, the membrane potential gets nearer to K nerst potential
this is called hyperpolarization
