KINESIOL 2Y03 Lecture Notes - Lecture 10: Myelin, Cardiac Muscle, Serotonin

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7 Nov 2022

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Neurotransmiss on (cid:8869) incoming messages the surface of axon. 4 as not flows into the cell during depolarization, voltage. Action potential spreads over of adjacent greas is affected. 4 ap"s occur at one spot on membrane but, regions (cid:8869) ap"s don"t "move" - one stimulates another in adjacent location. 4 movement of tions =local current yelinated axon. Ranvier to another saltatory conduction: local current flows blw nodes of ranvier. 4 voltage gated nat channels concentrated at nodes: uses less atp-energy efficient 4 flow of ap"s is much faster. "leaping" effect factors affecting propagation speed axon diameter (cid:8869)x sa= 4voltage - gated nat channels = faster local current. Amount of myelination is heavy myelination > light myelination. 4 large diameter, myelinated, conduct at 15-20m/s (cid:8869) motor neurons supplying skeletal and most sensory neurons. Ype b (cid:8869)medium diameter, lightly myelinated, conduct at 3-15m/s. Type ( (cid:8869)small diameter, rumyelinated, conduct at 2m/s or less.

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29. The action potentialâ¨

a. begins with the membraneâs increased permeability to potassium.

b. returns to resting when the sodium channels open.â¨

c. can be triggered by opening of ligand gated Na and K channels.â¨

d. involves voltage-gated Chloride channels in the membrane.â¨

e. can be triggered by opening of voltage gated Na+ and K+ channels.

30. Which of the following is not a step in the propagation of action potentials?

â¨a. Sufficient local inward current causes the axon to reach threshold.

â¨b. Local depolarization/inward current spreads to adjacent axonal regions.â¨

c. Adjacent regions eventually reach threshold and exhibit an action potential waveform.

â¨d. Current/depolarization continue to spread directionally along the axon, repeating steps aâc

e. All of the above are steps contributing to the propagation of action potentials.

31. Which of the following is important for the unidirectional propagation of action potentials?

a. The voltage dependence of the sodium channels

â¨b. The voltage dependence of the potassium channels

â¨c. The presence of a refractory period at a location where an action potential has just fired

d. Sufficient âleakinessâ of the axons, such that backward propagation of action potentials is prevented

â¨e. The capacity of axons to function as perfect insulators and prevent current leakage and backpropagation

Explain and report on:

(1) The physics underlying the propagation of action potential in myelinated vs. unmyelinated axons.

(2) The mechanism by which voltage gated ion channels sense and respond to changes in membrane electrical potential.

Describe how action potentials are propagated along a myelinated axon. How does the process differ in unmyelinated axons?

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KINESIOL 2Y03 Lecture Notes - Lecture 10: Myelin, Cardiac Muscle, Serotonin

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