Action Potential

Also called

nerve impulse · resting potential · resting membrane potential · depolarisation · repolarisation · hyperpolarisation · threshold · sodium channel · potassium channel · voltage-gated channels · sodium-potassium pump · polarised membrane · myelin sheath · node of Ranvier · saltatory conduction · refractory period · conduction of nerve impulse · तंत्रिका आवेग · क्रिया विभव · विश्रांति विभव

Topics

• A resting axon membrane is polarised: more K⁺ and negative proteins inside, more Na⁺ outside, about −70 mV inside.
• The sodium–potassium pump keeps it so, moving 3 Na⁺ out for every 2 K⁺ in…
• A stimulus that lifts the potential past the threshold (about −55 mV) opens voltage-gated Na⁺ channels: Na⁺ rushes in.
• The inside swings positive, to about +30 mV: this reversal of polarity is the depolarisation, the action potential.
• Na⁺ channels close and K⁺ channels open; K⁺ leaves and the inside returns to negative: repolarisation…
• The depolarised patch makes the next patch reach threshold, so the impulse travels along the axon in one direction.
• On a myelinated axon only the nodes of Ranvier are bare, so the impulse jumps node to node: fast, saltatory conduction.
• For a few milliseconds after a spike the Na⁺ channels cannot reopen: the refractory period, so impulses cannot pile up.

About this model

A GLB file of about 532 KB, shown in Lably's 3D viewer and, on a phone, placed in your room with AR. Credit: Model, science and animation: Lably (built procedurally with three.js; no downloaded meshes). | CC BY 4.0. Original geometry and animation made for Lably.

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