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Membrane potential

Madarász Tamás

PTE-ÁOK Department of Biophysics

Structure of cell membrane

Transport

Active transport is the movement of molecules across a membrane from a region of their lower concentration to a region of their higher concentration.primary active transport that uses ATP.secondary active transport that uses an electrochemical gradient.Carrier proteins:- Uniporter is an integral membrane protein that transports a single

type of substrate species (charged or uncharged) across the cell membrane.

- Symporter: transports two different type substrate across the cellmembrane.

- Antiporter: transports two or more different molecules or ions across the membrane.

Passive transport: It does not require an input of cellular energy because it is instead driven by the tendency of the system to grow in entropy.

Diffusion will continue until this gradient has been eliminated.Passive osmosis and diffusion: Some substances (small molecules, ions) such as carbon dioxide (CO2) and oxygen (O2), can move across the plasma membrane by diffusion, which is a passive transport process.

Passive transport

106 ions per second or greater

http://physiology.elte.hu/eloadas/kiegtanar_elettan/potencial_neuro_2009.pdf

Channel Channel

Membrane

Filter region

Gate

Intracellular fluid

•Calcium-activated potassium channel - open in response to the presence of calcium ions or other signalling molecules.•Inwardly rectifying potassium channel - passes current (positive charge) more easily in the inward direction (into the cell).•Tandem pore domain potassium channel - are constitutively open or possess high basal activation, such as the "resting potassium channels" or "leak channels" that set the negative membrane potential of neurons.•Voltage-gated potassium channel - are voltage-gated ion channels that open or close in response to changes in the transmembrane voltage.

Potassium ion channels

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Active transport

Three sodium ions are exported and two potassium ions are imported

Main components

•water

•Ions

– Cations (K+, Na+, Ca2+)

– Anions (Cl-, H2PO4− and

HPO42−)

•Proteins–with negative charge (pH! – isoelectric point)

Membrane potential

• Membrane potential is the difference in electric potentialbetween the interior and the exterior membrane side.

Nerve impulse transmission

http://physiology.elte.hu/eloadas/kiegtanar_elettan/potencial_neuro_2009.pdf

Muscle and nerve tissue are electrically excitable

Muscle and nerve tissue are electrically conductive

Donnan potential

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Bernstein potassium hypothesis

-K+ ions are responsible for resting membrane potential

-Reason:

-cellmembrane is selectively permeable for K+ ion

-There are different K+ ion channels

Bernstein potassium hypothesis

Electric gradient

potassium gradient

The higher concentration page will be negative potential.

Development of resting membrane potential1. The difference in concentration of the given ions

(chemical concentration gradient).R=universal gas constant

N=total amount of ions in mol

T= temperature

X1/X2=gradient

2. Charge difference (electrical gradient) between the two sides of the membrane.

Z= electrone numberF=Faraday’s constantE=potential

Nernst equation

F = 9.64853399(24)×104 C mol−1,

R = 8.314472(15) J K−1 mol−1,

Nernst potential

K+ + e- ⇌ K(S) E0=−2.931V

Nernst equation It show how much electrical potential is able to balance the concentration gradient.

out

in

Goldman-Hodgkin-Katz equation

The membrane potential is the result of a „compromise” between:-the various equilibrium potentials

-each weighted by the membrane permeability-absolute concentrationof the ions

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Types of receptors

Internal receptors that respond to changes inside the body are known as interoceptors. Example: baroreceptor in the vascular wall

Exteroceptor: a sense organ receiving stimuli from the external environment, as the eye or the heat receptors in the skin

Proprioceptor: Proprioception is mediated by proprioceptors, mechanosensory neurons located within muscles, tendons, and joints.