4. Conduction & Myelination

What is action potential conduction?

The process by which an action potential is propagated along an axon

Does an action potential change as it travels along an axon?

No the action potential remains identical in amplitude throughout the axon

What is conduction velocity?

The speed at which an action potential travels along an axon

Which two factors most influence conduction velocity?

Axon diameter and myelination

How does axon diameter affect conduction speed?

Larger axon diameters reduce internal resistance and increase conduction speed

Why do larger axons conduct action potentials faster?

They have lower resistance to ion flow within the cytoplasm

What effect does membrane resistance have on conduction speed?

Higher membrane resistance reduces ion leakage and increases conduction speed

Why are unmyelinated axons slower at conducting action potentials?

Because ions leak across the membrane and channels must open continuously along the axon

How is the action potential maintained in unmyelinated axons?

By sequential opening of voltage-gated sodium channels along the entire axon

What is myelin?

A lipid-rich insulating sheath that surrounds axons

What is the primary function of myelin?

To increase conduction speed by preventing ion leakage

Which glial cells form myelin in the CNS?

Oligodendrocytes

Which glial cells form myelin in the PNS?

Schwann cells

What are nodes of Ranvier?

Gaps between myelinated segments of an axon where voltage-gated sodium channels are concentrated

Why are nodes of Ranvier important for conduction?

They allow regeneration of the action potential along the axon

What is saltatory conduction?

The jumping of an action potential from one node of Ranvier to the next

Why is saltatory conduction faster than continuous conduction?

Because depolarization occurs only at nodes rather than along the entire axon

How does myelination reduce ion leakage?

Myelin forms a high-resistance barrier that prevents ions from crossing the membrane

What happens to sodium channel distribution in myelinated axons?

Sodium channels are concentrated at the nodes of Ranvier

What happens to conduction if myelin is damaged?

Conduction slows or may fail due to increased ion leakage

What is a demyelinating disease?

A condition in which myelin is damaged or destroyed

How does demyelination affect action potential propagation?

Depolarization may fail to reach threshold at the next node

Which disease is an example of CNS demyelination?

Multiple sclerosis

Why can demyelination cause conduction failure?

Because current dissipates before reaching the next node of Ranvier