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What are the two main factors that determine the speed of action potential conduction?

Axon diameter and myelination.

How does axon diameter affect conduction velocity?

Larger diameter axons have lower internal resistance, allowing current to spread further and depolarize longer segments of the axon, resulting in faster conduction velocity.

What is myelination?

The wrapping of axons by glial cells (oligodendrocytes in the CNS, Schwann cells in the PNS) that increases conduction velocity.

What are Nodes of Ranvier?

Gaps in the myelin sheath where voltage-gated Na+ and K+ channels are concentrated, allowing action potentials to 'jump' in saltatory conduction.

What is saltatory conduction?

The process by which action potentials 'hop' from one Node of Ranvier to the next in myelinated axons, significantly increasing conduction velocity.

What are the passive properties of neurons?

They include membrane resistance, internal resistance, and capacitance, affecting how far and how quickly current spreads along the axon.

What is capacitance in the context of neurons?

The ability of the membrane to store charge; larger neurons have more capacitance due to more membrane area.

How does internal resistance change with axon diameter?

Internal resistance decreases with increasing axon diameter due to a greater cross-sectional area.

What is the trade-off between internal resistance and membrane resistance in larger axons?

Larger axons have lower internal resistance but lower membrane resistance, yet the lower internal resistance allows for faster conduction.

What is multiple sclerosis (MS)?

A demyelinating disease where the immune system attacks myelin sheaths, slowing conduction velocity and can block action potential propagation.

What happens to conduction in axons with degenerated myelin?

Current leaks out through K+ channels under the myelin, reducing the amount of current reaching the next Node of Ranvier, slowing or blocking conduction.

What is the difference between myelinated and unmyelinated axons in terms of conduction velocity?

Myelinated axons conduct action potentials much faster due to saltatory conduction, while unmyelinated rely on continuous propagation.

What is a compound action potential?

The summed electrical activity of all axons in a nerve, measured by stimulating a nerve and recording the response.

What are the three components of a compound action potential?

A fibers: Fastest, myelinated; B fibers: Slower, myelinated; C fibers: Slowest, unmyelinated.

How does conduction velocity testing help diagnose neurological diseases?

It reveals slowed or blocked conduction, indicating diseases like multiple sclerosis (MS) and amyotrophic lateral sclerosis (ALS).

What is the difference between orthodromic and antidromic conduction?

Orthodromic: Action potentials travel in the normal direction; Antidromic: Action potentials travel in the opposite direction.

Why do vertebrates have both myelinated and unmyelinated axons?

Myelinated axons are used for rapid signal transmission, while unmyelinated axons are used for slower processes.

What is the role of glial cells in myelination?

Oligodendrocytes myelinate axons in the CNS, while Schwann cells myelinate axons in the PNS, increasing conduction velocity.