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.