RESTING MEMBRANE POTENTIAL - PowerPoint Presentation

Slide1

RESTING MEMBRANE POTENTIAL

By

Dr.

Ayisha

Qureshi

Assistant Professor, Physiology

MBBS, MPhilSlide2

OBJECTIVES

By the end of this lecture, you should be able to:

Define Nernst potential

Use the Nernst equation to calculate the values of Nernst potential for Na, K & Cl

Define and give the

physiological basis of Resting membrane potential

Use the

Goldmann

-

Hoghkin

-Katz equation to calculate the RMP

Explain the contribution of Sodium-Potassium Pump to the RMPSlide3

REMEMBER:Slide4

CONCENTRATION GRADIENT:Slide5

REMEMBER:

A

concentration gradient can exist for molecules/ particles and ions. Thus, a

CHEMICAL gradient

can exist in the presence of an

ELECTRICAL gradient

. Slide6

LIPID BILAYER

The membrane is electrically NEUTRAL!

The membrane carries NO charge!

The membrane is SELECTIVELY permeable.Slide7

SEMIPERMEABLE MEMBRANESlide8

If the membrane is impermeable or semi-permeable, THEN,

How do we make it selectively permeable to a specific ion?Slide9

The Role of Ion ChannelsSlide10

The role of Ion channels

The ion channels can be of 2 main types:

Leak channels:

Include ion channels specific for Na

+

, K

+

,

Cl

-

etc. As long as the size of the ion is appropriate, the ion will go through them.

2.

Gated channels:

The gates are part of the protein channel and can open or close in response to certain stimuli.

Ligand Gated Channels

– Channels which are opened through ligand binding (the ligand can be a hormone or a neurotransmitters or some other chemical.)

Voltage Gated Channels

– Channels which are opened by changes in the membrane potentialSlide11

Nernst equilibrium/ Equilibrium potential: Slide12

ECF:

Less +, more -

ICF

:

more +, less

-Slide13

ECF:

ICF:

Slide14

ECF:

3+, 5-

ICF:

5

+, 5-Slide15

NERNST EQUILIBRIUM/ EUILIBRIUM POTENTIAL

“

The membrane potential at which the

electrical gradient

exactly opposes the concentration or

chemical gradient

is called the Equilibrium potential.”

It is calculated by the Nernst equation.

At this potential, the net movement of that particular ion STOPS. Slide16

NERNST EQUATION

The Nernst equation can be used to calculate Nernst potential for any

univalent ion

at normal body temperature:

EMF= ±61 log

Conc

. Inside

Conc

.

OutsideSlide17

Physiological basis of resting membrane potential in a nerve fibre:Slide18
Slide19

MEMBRANE POTENTIAL

DEFINITION:

The separation of charges across the membrane.

OR

The difference in the relative number of

cations

& anions in the ICF & ECF.Slide20

RESTING MEMBRANE POTENTIAL

DEFINITION:

The constant membrane potential present in the cells of excitable & non-excitable tissues when they are at rest (i.e. when they are not producing any electrical signals) is called their Resting membrane potential. Slide21

We know that the Resting Membrane Potential of human nerve cell membrane is —90

mv

.

What is the Physiological Basis of this RMP & how is it calculated??Slide22

Resting Membrane Potential in Neurons

There is a great difference in the chemical composition of nerve cell interior(ICF) & exterior (ECF).

ECF

:

ICF

Na

+

:- 142 : 14

K

+

:- 4 : 140

The nerve cell

interior (ICF)

is rich in

potassium ions (K)

and

negatively charged proteins

while the

ECF

is rich in

Sodium

&

Chloride

ions.Slide23

Various ions try to diffuse from one side of the membrane to the other depending upon their electrochemical

gradients:Slide24

The neuron plasma membrane at rest is

100 times

more permeable to K ions than to the Na ions!!!!

This is through the help of the

Potassium

leak channels....Slide25
Slide26

So, Now:

Electrical gradient Chemical gradient

for K

+

for K

+

This is the

membrane potential at which the

electrical gradient

exactly opposes the concentration or

chemical gradient

and it is

called the Equilibrium

potential or the Nernst Potential for Potassium.

Using the Nernst equation, when the

Nernst potential for Potassium

is calculated, it is -94 mv. Slide27

CALCULATING THE RMP:

The

R

MP can be calculated using one of the 2 equations:

NERNST EQUATION

GOLDMAN’S OR GOLDMANN-HODGKIN-KATZ EQUATIONSlide28

Calculating the RMP by the Nernst Potential:

Potassium ions:

Nernst Potential for

K+

= —94mv

Sodium ions:

A very small number of Sodium ions move to the inside of the nerve cell despite a low permeability of the membrane to the

Sodium

ions. This is because of the small no. of Sodium leak channels present. They make a contribution of a small amount of electro positivity to the cell interior.

Its value is=

+8mv

Sodium-Potassium Pump:

expels 3 Na

+

in exchange for 2 K

+

.

It contributes=

—4 mv

So the total Resting Membrane Potential of a nerve cell is:

RMP= —94 +8 —4 (mv)

= —90 mv Slide29

Calculating the RMP by the

GOLDMAN-HODGKIN-KATZ equation:

Has

3

advantages:

It keeps in mind the concentration gradients of each of the ions contributing to the RMP.

It keeps in mind the membrane permeability of all the ions contributing to the RMP

It can thus be used to calculate the RMP when multiple ions are involved rather than when only single ions are involved.

EMF= 61.log

C

Na

i

.

P

Na

+

C

k

i

.

P

k

+

C

cl

o

P

cl

C

Na

o

.

Pna

+ Cko.Pk +

CcliPcl

= —90 mvSlide30

PHYSIOLOGICAL BASIS OF THE RMP:

-Calculation through the Nernst Equation (

Mushtaq

: chapter: 2, NEURONS & SYNAPSES, page: 102-108, 5

th

edition).

- Calculation through the Goldman-Hodgkin-Katz equation (Guyton: chapter 5, page: 59-60, 12

th

edition)Slide31

RMP

POINT TO NOTE:

Resting Membrane Potential is

DETERMINED

by the

POTASSIUM IONS

and has a value of

‒

90 mv.