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Flashcard 1

Q: What are the two main factors that determine the speed of action potential conduction?
A: Axon diameter and myelination.

Flashcard 2

Q: How does axon diameter affect conduction velocity?
A: Larger diameter axons have lower internal resistance, allowing current to spread further and depolarize longer segments of the axon, resulting in faster conduction velocity.

Flashcard 3

Q: What is the relationship between membrane resistance and axon diameter?
A: Larger diameter axons have more K+ channels, which decreases membrane resistance and increases current leakage. However, the effect of lower internal resistance in larger axons dominates, leading to faster conduction.

Flashcard 4

Q: What is myelination, and how does it affect conduction velocity?
A: Myelination is the wrapping of axons by glial cells (oligodendrocytes in the CNS, Schwann cells in the PNS). It increases membrane resistance, reduces current leakage, and allows saltatory conduction, which greatly increases conduction velocity.

Flashcard 5

Q: What are Nodes of Ranvier, and why are they important?
A: Nodes of Ranvier are gaps in the myelin sheath where voltage-gated Na+ and K+ channels are concentrated. They allow the action potential to "jump" from node to node in a process called saltatory conduction.

Flashcard 6

Q: What is saltatory conduction?
A: Saltatory conduction is the process by which action potentials "hop" from one Node of Ranvier to the next in myelinated axons, significantly increasing conduction velocity.

Flashcard 7

Q: What are the passive properties of neurons, and how do they affect conduction?
A: Passive properties include membrane resistance, internal resistance, and capacitance. These properties determine how far and how quickly current spreads along the axon, influencing conduction velocity.

Flashcard 8

Q: What is capacitance in the context of neurons?
A: Capacitance is the ability of the membrane to store charge. Larger neurons have more capacitance because they have more membrane area, requiring more charge to change the membrane potential.

Flashcard 9

Q: How does internal resistance change with axon diameter?
A: Internal resistance decreases with increasing axon diameter because larger axons have a greater cross-sectional area, allowing current to flow more easily.

Flashcard 10

Q: What is the trade-off between internal resistance and membrane resistance in larger axons?
A: Larger axons have lower internal resistance (faster current flow) but lower membrane resistance (more current leakage). However, the effect of lower internal resistance dominates, leading to faster conduction.

Flashcard 11

Q: What is multiple sclerosis (MS), and how does it affect conduction?
A: MS is a demyelinating disease where the immune system attacks myelin sheaths. This increases current leakage, slows conduction velocity, and can eventually block action potential propagation.

Flashcard 12

Q: What happens to conduction in axons with degenerated myelin?
A: In degenerated myelin, current leaks out through K+ channels under the myelin, reducing the amount of current reaching the next Node of Ranvier. This slows or blocks action potential conduction.

Flashcard 13

Q: What is the difference between myelinated and unmyelinated axons in terms of conduction velocity?
A: Myelinated axons conduct action potentials much faster than unmyelinated axons due to saltatory conduction. Unmyelinated axons rely on continuous propagation, which is slower.

Flashcard 14

Q: What are the fastest conducting axons in the human body, and how fast can they conduct?
A: The fastest conducting axons are large-diameter myelinated axons, which can conduct action potentials at speeds up to 120 meters/second.

Flashcard 15

Q: What is a compound action potential, and how is it measured?
A: A compound action potential is the summed electrical activity of all axons in a nerve. It is measured by stimulating a nerve and recording the response at different points along the nerve, revealing the conduction velocities of different axon types.

Flashcard 16

Q: What are the three components of a compound action potential, and what do they represent?
A:

1. A fibers: Fastest, myelinated, responsible for motor and touch sensations.

2. B fibers: Slower, myelinated.

3. C fibers: Slowest, unmyelinated, responsible for slow pain and temperature sensations.

Flashcard 17

Q: How does conduction velocity testing help diagnose neurological diseases?
A: Conduction velocity tests can reveal slowed or blocked conduction in diseases like multiple sclerosis (MS) and amyotrophic lateral sclerosis (ALS). In MS, myelinated fibers are affected, while in ALS, motor neurons are selectively damaged.

Flashcard 18

Q: What is the difference between orthodromic and antidromic conduction?
A:

• Orthodromic conduction: Action potentials travel in the normal direction (e.g., from neuron to muscle).

• Antidromic conduction: Action potentials travel in the opposite direction (e.g., from muscle back to neuron).

Flashcard 19

Q: Why do vertebrates have both myelinated and unmyelinated axons?
A: Myelinated axons are used for rapid signal transmission (e.g., motor and sensory signals), while unmyelinated axons are used for slower processes (e.g., autonomic functions like digestion and temperature regulation).

Flashcard 20

Q: What is the role of glial cells in myelination?
A: Oligodendrocytes myelinate axons in the CNS, while Schwann cells myelinate axons in the PNS. They wrap their membranes around axons to form the myelin sheath, increasing conduction velocity.