Action potentials

An ion channel is a integral membrane protein that forms a selective pore to allow ions to pass through cells

gated ion channels sometimes require a ligand which will cause them to change shape so that the ions can diffuse through.

myasthenia gravis - autoimmune disease, body makes antibodies that attack acetylcholine receptors so acetylcholine cannot bond. This causes paralysis.

Some gated ion channels are opened by action potential - when the electric field changes the protein changes shape (causes a conformational change). These are voltage gated channels.

• when the charge reaches the membrane potential the NA+ channels open which creates a positive feedback loop. leading to quick depolarization.

• the membrane potential will become positive as the concentration gradient changes.

• after a certain point the Na+ gates close and the K+ gates open causing repolarization.

• the action potential is all or nothing, the membrane potential must be reached for the process to happen (so enough neurotransmitter must be released)

• potassium ions are concentrated inside the cell, sodium ions are concentrated outside

travel of the action potential:

• Na+ channels are sensitive to electric fields

• Electric fields act at a distance - depolarization of one region of membrane will trigger the opening of channels in adjacent regions of membrane