Introduction to Physiology

Kamal Mohammad 0912683842

Faculty Of Medicine Dept.Of Physiology

Membrane potential and

Resting membrane potential

Faculty Of Medicine2nd Year Semster4

Membrane Potential

Membrane Potential : The difference in ionic

distribution between inside and outside of cells

which results in electrical potential difference

across the cell membrane.

Charged Substances in Body Fluids

Many molecules in our body fluids have electrical

charges due to the presence of negative groups (e.g.

phosphate, RCOO-) or positive groups such as RNH3+.

Also most mineral elements such as sodium, potassium,

chloride, and calcium (Na+, Cl-, K+, Ca++) present in our

body fluids as ions.

Positive Charges Negative Charges

Na+

K+

Ca++

Mg++

RNH3+

Cl_

HCO3

-

PO42-

Proteins

Fixed Anions

Distribution of Main Charged Substances in Body

Fluids

Na+

Na+Na+

Cl_

Cl_

Cl_ Cl

_

Cl_

Cl_

Cl_

Cl_

Cl_

Na+

Na+ Na+

Na+

Na+

Na+

Na+ Cl_

Cl_ K+ K+

K+

K+

K+

K+

K+K+

K+

K+

K+

K+

_ _

FIXED ___

_ _

FIXED ___

_ _

FIXED ___

_ _

FIXED ___

_ _

FIXED_

__

CELLECF

Properties of Charged Chemicals

Distribution of various charges outside and

inside the cell play a significant role in cell

function. Excitable cells such as muscle and

nerve use this phenomenon to generate and

propagate electrical signals.

Properties of Charged Chemicals

Like charges repel each other.

+ +Electrical

Force

_ _Electrical

Force

Opposite charges attract each other.

+_Electrical

Force

This creates force at

opposite direction

of each charge.

Distribution of Charges

Distribution of Charges The membrane potential is due to small excess of

negative ions inside of the cell and small excess of

positive ions outside of the cell.

The negative charges are attracted to the positive

charges and they form a thin layer of negative inside

and positive outside of the cell.

The rest of intracellular and extracellular fluid remain

neutral.

Resting Membrane potential

In excitable cells the potential difference

between inside and outside of the cell during

rest is called “resting membrane potential”

RMP

The difference in potential across the cell membrane can

be measured by special device called the cathode ray

oscilloscope (voltmeter)

Using electrodes placed on the two sides of the

membrane

The magnitude of the RMP differs in different types of

cells , for example :-

In muscle cell = -90 m V

In a nerve cell = -70 m V

Membrane Potential Can be Measured

The potential difference across the cell membrane can

be measured using microelectrodes and a sensitive

voltmeter.

Causes of RMP

Membrane Potential

_ _

FIXED ___

K+

K+

Na+Na+

ATP

2 K+

3 Na+

Gated Na+

Channel

Gated K+

Channel

Non-gated K+

Channel

Sodium potassium

leak channels

The resting cell membrane is 50-100 times more

permeable to K+ than to Na+

K+ tends to leak out side of the cell down its

concentration gradient, carrying positive charge with it,

K+ moves easily but Na+ with difficulty why ?

1- the membrane Na+ channels are closed under resting condition, while the K+ channels are open (leak

channels)

2-The Na+ channels are guarded by Ca2+ from outside that form gates which repel Na+ and prevent its entry under resting condition

(2) The Na+ -K+ pump

• It transmits 3 Na+ ions to the outside for each 2 K+ ions transmitted to the inside of the membrane .

• This pump causing a potential difference (creating negativity inside & positivity outside).

• The pump is an active process

(3) Presence of non diffusible anions inside the nerve fibers

These anions include: Proteins and other organic molecules in the cell.

are negatively charged (anions),

can not cross the cell membrane therefore this makes inside of the cell negative

These fixed anions does not pass through the cell

membrane due to:

1.Their large molecular weight

2.Repelling by proteins in the cell membrane

_ _

FIXED ___

High resistance

Development of the RMP (SUMMARY)

Membrane permeability is greater for K+ than to Na+ , thus more

K+ leave the inside of the cells through the leak channels

The Na+ -K+ pump causes more transport of the positive (3Na+)

than to the inside (2K+).

Most of the negative ions inside the nerve fibers are non

diffusible and remain inside

The inside becomes negative while the

out side becomes positive

ANY

QUESTION????????Any Question

Answer the following question:

(1)What is the resting membrane potential

(2)How the membrane potential was measured

(3)Factors responsible for genesis of the resting membrane potential

(4)Discuss the role of the sodium potassium pump in the genesis of the membrane potential

THANK YOU