membrane potentials and action potentials

Question 1

the potential difference of 94 millivolts inside is when?

Answer 1

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

Question 2

the potential difference is 61 millivolts in the inside when?

Answer 2

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

Question 3

when membrane is permeable to more ions the diffusion potential depends on?

Answer 3

1. POLARITY of electric charge of each ions
2. the concentration of each ions to the inside and outside
3. the permeability of membrane to each ion

Question 4

what is Goldman equation

Answer 4

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)

Question 5

what several key points become evident from Goldman equation?

Answer 5

1. Na, K, cl ions are the most important ions involved in the development of membrane potential
2. the quantitative importance of each of these ions in measuring membrane potential is equal to their permeability across the membrane
3. positive ion concentration gradient from inside to outside will cause the inside to be electronegative and vice versa when there is negative ion concentration
4. permeability of K and Na ions change but Cl doesnt
   change throughout of nerve impulse transmission

Question 6

how measuring of membrane potential is done

Answer 6

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

Question 7

resting membrane potential of large fibers when they are not transmitting impulse

Answer 7

it is -70 millivolts, which tells its more negative in the inside to the outside

Question 8

gradient for Na outside and inside is

Answer 8

142 and 12 mEq/L

Question 9

gradient for K outside and inside

Answer 9

4 and 140 mEq/L

Question 10

if K ions were the only ions causing resting potential, the potential would be?

Answer 10

-94 millivolts

Question 11

using goldman eq to measure the membrane potential caused by K and Na ions is?

Answer 11

-86 millivolts

Question 12

net membrane potential is what and how?

Answer 12

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

Question 13

what is action potentail

Answer 13

the rapid change in the membrane potential that is spread rapidly along a nerve fiber membrane

Question 14

resting stage of action potential

Answer 14

it is -70 millivolt. the membrane is said to be polarized in this stage.

Question 15

depolarization of action potential?

Answer 15

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

Question 16

necessary factor for depolarization and repolarization

Answer 16

voltage gated Na channel and voltage gated K channel

Question 17

when does activate sodium channel open

Answer 17

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

Question 18

inactivation Na channel close

Answer 18

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

Question 19

voltage gated potassium channel and its activation

Answer 19

it gets activated when the membrane potential increases from -70 to zero millivolts and cause the efflux of K ions the outside.

Question 20

threshold for stimulation is?

Answer 20

-55 millivolts

Question 21

all or nothing principal ?

Answer 21

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.

Question 22

safety factor for propogatiom

Answer 22

the ratio of action potential to threshold for excitation must be greater than 1.

Question 23

plateau in some action potentials is causes by what factors

Answer 23

fast opening sodium channels, slow sodium calcium channels and the slow K channels (VOLTAGED GATED) and takes place in cardiac muscles.

Question 24

which drug causes a repititive discharge from cells like skeletal and large nerve fibers?

Answer 24

veratridine.

Question 25

myelin sheath is deposited by what >

Answer 25

it is deposited by Schwann cells.

Question 26

around axon there is multiple layer of what

Answer 26

Schwann cells membrane containing sphingomyelin lipid

Question 27

node of ranvier?

Answer 27

the junction between each 2 successive Schwann cells which is 2-3 micrometers is where the ions can still flow with ease through axon

Question 28

any factor that causes the Na ions to move inward sets off?

Answer 28

automatic regenerative opening of Na channels

Question 29

what are the factors that can open the automatic regenerative Na channels?

Answer 29

any mechanical disturbance, chemical effects or passage of electricity

Question 30

absolute refectory period?

Answer 30

the period during which a 2nd action potential cannot be elicited when when a strong stimulus is given.

Question 31

what happens when equal number of positive ions from the outside to the inside what is the membrane potential?

Answer 31

it changes from -70 millivolts to +35 millivolts.

Question 32

why the membrane potential is -86 inside the cell when measured by goldman equation

Answer 32

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.

Question 33

how the full recovery of resting membrane potential occurs

Answer 33

the closure of na channels and the efflux of K ions outside the cell speed up the repolarization state.

Question 34

when threshold potential is reached

Answer 34

it is reached when the number of Na ions diffusing inside of the cell are greater than the K ions diffusing outside.

Question 35

how sodium and potassium ionic gradient is re established

Answer 35

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

Question 36

special feauture of NA-k atp pump is?

Answer 36

degree of atcivity is strongly stimulated when the accumalation of Na ions is more inside.

Question 37

the concentration of na increases from what to what causes the activity of pump increases what fold?

Answer 37

it increases from 10-20 mEq/L the activity increases 8 fold

Question 38

the rhytimcal discharge causes

Answer 38

the rhythmical beating of the heart 
rhythmical peristalsis of intestines
rhythmic breathing (neuronal events)

Question 39

skeletal muscles or large nerve fibers discharge when placed in?

Answer 39

veratridine

Question 40

why heart membrane does not depolarize immedetaile after it repolarizes

Answer 40

potassium conductance

Question 41

hyperpolarizatiom

Answer 41

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