Potentials Membrane agus Pòlaichean Gnìomh

Potentials of the Membrane and Action Potentials

• Electrical potentials exist across membranes in almost all body cells.
• Nerve and muscle cells create rapid electrochemical impulses for signal transmission.
• Other cell types – such as glandular cells, macrophages, and ciliated cells – also experience changes in membrane potential affecting cellular functions.
• Electrical potentials arise from ion concentration differences across selectively permeable membranes.

Basic Membrane Potentials

• Potassium (K+) ion concentration is high inside nerve fibre membranes but low outside.

• If the membrane is only permeable to K+, K+ ions diffuse out, creating positive charge outside and negative charge inside (because of trapped anions).

• A diffusion potential arises, preventing further net K+ outflow.

• In mammals, this resting potential is roughly -94mV.

• Sodium (Na+) ions have a high concentration outside and a low concentration inside a nerve fibre membrane.

• If the membrane is only permeable to Na+, positive Na+ ions diffuse inside creating a positive membrane potential inside.

• A diffusion potential is created.

• In mammals, this potential is about +61mV.

• The Nernst Equation can calculate the diffusion potential for a particular ion at a particular temperature, depending on concentration differences across a membrane.

• EMF (millivolts)= ±61/Z × ln(internal concentration/external concentration)

Goldman Equation

• When a membrane is permeable to multiple ions, the Goldman Equation, or Goldman-Hodgkin-Katz equation calculates the membrane potential. This takes into account ion valence, membrane permeability, and ion concentration on either side of the membrane.
• EMF(millivolts)=-61 × ln((P Na+[Na+]o +(P K+[K+]o+ (P Cl−[Cl−]i)/(P Na+[Na+]i +(P K+[K+]i−(P Cl−[Cl−]o)))

Resting Membrane Potential

• Varied resting membrane potentials across different cell types, ranging in mammals from -85 to -90mV.
• The exact potential depends on the specific combination of ions and their permeabilities.
• Key ions include sodium, potassium, and chloride.

Electrochemical Driving Force

• When multiple ions contribute to a membrane potential, there is an electrochemical driving force for each ion, the difference between the membrane potential and the ion's equilibrium potential.

Tha poileagan dealain ann an crochadh air membrane a' toirt buaidh air fuireach nan ceallan san corp. Bidh ceallan neural is fèithe ag cruthachadh brosnachadh electrochemical a' toirt taic do cho-bhitean. Tha an quiz seo a' toirt seachad sealladh farsaing air na poileagan a tha a' leantainn bho dhiofar shailean ion. Tha e freagairteach do dhaoine a tha ag ionnsachadh mu phòlaichean membrane.