Membrane and Action Potential [Gen Physio]

8/3/2019 Membrane and Action Potential [Gen Physio]

1/24

MA. BEMERLY P. JARDIOLIN-SIRA, MDPATHOLOGIST


2/24

Electric potentials exist across the

membranes of ESSENTIALLY ALL cells of

the bodyBut FEW CELLS are excitable they are

capable of self-generation of

electrochemical impulses at their

membranes impulses can be used totransmit signals along the membranes


3/24

Macrophages, ciliated cells,

glandular cells : changes in their

membrane potentials playsignificant roles in controlling

many of the cells functions


4/24

1. impermeable to intracellular1. impermeable to intracellular

proteins and other organic anions ( Aproteins and other organic anions ( A-- ))

2. moderately permeable to Na+2. moderately permeable to Na+3. freely permeable to3. freely permeable to ClCl-- and K+and K+


5/24

NORMALLY: the K+ conc is GREAT INSIDE themembrane, while OUTSIDE the membrane,gradient is LOW

Because of the LARGE K+ concentration gradientfrom the inside toward the outside strongtendency for K+ to diffuse outward the outside

As K+ moves outside, it carries positive chargesto the outside => ELECTROPOSITIVITY OUTSIDE

& ELECTRONEGATIVITY INSIDE (due to theremaining negative ions that remain behind anddo not diffuse outward along with the K+)


6/24

The new POTENTIAL DIFFERENCE (+

outside, - inside) repels the positively

charged K+ continually diffusing outwardback in the opposite direction, from the

outward toward the inside

Within Millisec, the potential change

becomes incredibly increased blockade of further net diffusion to the

exterior


7/24

Potential Difference is 94 MV,

with negativity inside the fiber

membrane( if this a mamaliannerve fiber)


8/24

IF Na+ is involved: Inc conc of Na+ OUTSIDE the membrane,

low conc of Na+ INSIDESodium is positively charged, and the

membrane is impermeable to all otherions, BUT highly permeable toNa+

With diffusion of Na+ towards the INSIDE=> change in polarity =>ELECTROPOSITIVITY INSIDE &ELECTRONEGATIVITY OUTSIDE


9/24

Again, within Millisec, the membrane

potential rises high enough => Blockade

of further diffusion of Na+ to the inside Potential Difference is 61 MV,with

positivity inside the fiber membrane


10/24

The concentration difference ofThe concentration difference of

IONS across a selectivelyIONS across a selectively

permeable membrane cause thepermeable membrane cause thecreation of MEMBRANEcreation of MEMBRANE

POTENTIALPOTENTIAL


11/24

Particle sizeParticle size ions in the body are

hydrated so although K+ is

larger than Na+, hydrated Na+ islarger than hydrated K+


12/24

Ion channels ions cross membranes via

ion channels rather than simple

pores and these channels arepassages through protein

molecules, therefore, there are

separate Na+, K+ & Cl- channels


13/24

VOLTAGEVOLTAGE the ease with which ions

pass through some of these

channels is controlled by voltage- the passage of Na+ through

Na+ channels in excitable tissues

( muscles and nerves ) is greatly

increased by a decrease inmembrane potential


14/24

NeurotransmittersNeurotransmitters these agents may

bind to receptors associated with the ions

and can bring ease with which ions passthrough some of the channels


15/24


16/24

example: Cl ions are present in higher

concentration in the extracellular fluid

than in the cell interior=

>=>

they tend todiffuse into the cell


17/24

example: the interior of the cell is

negative compared to the exterior

area, therefore, Cl- ions are pushedout of the cell

** so, after sometime an equilibrium is

reached and Cl influx will be equal

to Cl efflux


18/24

K+ = concentration gradient is outward,

electrical gradient is inwardNa+ = chemical gradient is inward,

electrical gradient is also inward

Cl - = concentration gradient is inward,

electrical gradient is outward


19/24

FOR K+ and Na+ ions => intracellular

concentration remains constantbecause there is an ACTIVE TRANS-

PORT of Na+ out of the cell against

its electrical and concentration

gradients and also an ACTIVETRANSPORT of K+ into the cell


20/24

This ACTIVE TRANSPORT is called

SODIUM-POTASSIUM PUMP ==>==>

responsible for the active transport ofNa+ out of the cell and K+ into the

cell ( extrudes 3 Na+ from the cell for

each 2 K+ it takes into the cell )


21/24

Ca++ = intracellular concentration is

very low => electrical and

concentration gradients areBOTH directed inward

** the distribution of ions across cell

membrane and the nature of thismembrane are responsible for the

presence of MEMBRANE POTENTIAL


22/24

Na+ is actively transported out of the

cell and K+ is actively transported in

K+ diffuses back out of the cell becauseof its conc gradient and Na+ diffuses

back in

Since the permeability of the membrane

to K+ is much greater than it is to Na+ ATREST, the passive K+ efflux is much

greater than the passive Na+ influx


23/24

Since the membrane is impermeable

to most of the anions in the cell, the

K+ efflux is not accompanied by anequal flux of anions and the

membrane is maintained in a

polarized state ( the interior of the

cell is negatively charged and theexterior area is positively charged )


24/24

Membrane and Action Potential [Gen Physio]

Documents

Transcript of Membrane and Action Potential [Gen Physio]