KINESIOL 1Y03 Lecture Notes - Lecture 15: Saltatory Conduction, Neuroglia, Neurotransmission

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3 Sep 2018

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An action potential spreads over the surface of an axon. Aps are caused by the initial depolarization to reach threshold at the trigger zone; creates all or nothing principle. As na flows into the cell during depolarization, the voltage of adjacent areas is affected and their voltage-gated na channels open; increase in positive charge triggers neighbouring voltage gates. The traveling of action potentials is called nerve impulses. Continuous conduction: along the whole axon we have na k leak channels (evenly distributed), na k voltage gated ion channels and na k pumps. Has neuroglial cells surround the axon only once (cns = oligodendrocytes, pns = schwann cells) Reason is because of a large graded potential triggers first voltage gated channel that will then trigger the. Ap occurs at one spot on a membrane but have the ability to propagate by stimulating adjacent regions. Technically ap do not move along the axon, on ap stimulates another ap in an adjacent location.

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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

Santiago Ramon y Cajalâs theory of dynamic polarization refers to the:

(a)membrane potential of a neuron at rest.

(b)membrane potential of a neuron firing action potentials.

(c)opening and closing of gated channels in the membrane.

(d)one way flow of information in neurons from dendrites to axon terminals.

(e)one way flow of information in neurons from axon terminals to dendrites.

Over the course of scientific history, there are many examples of scientists reaching the right conclusion for the wrong reasons. When Schwann first proposed that the nervous system was made of individual cells, he based it on observations of:

(a)synapses.

(b)dendrites

(c)axon terminals.

(d)astrocytes.

(e)Nodes of Ranvier.

The synaptic cleft was finally seen in the 1950s. What prevented scientists from seeing it earlier?

(a)The resolution of the light microscope.

(b)They were looking in the wrong place.

(c)Their tissue was not appropriately stained.

(d)Myelination of the axons.

(e)all of the above

The resting membrane potential of a neuron is approximately:

(a) +65 V

(b) +65 mV

(d) -65 mV

What is largely responsible for the resting membrane potential in a neuron?

(a)Axonal insulation by myelin

(b)Voltage-Gated Sodium Channels

(c)The Action Potential

(d)Potassium Leak Channels

Which of the following would DECREASE the propagation velocity of an action potential down an axon?

(a)Increase in axon diameter

(b)Increase myelination between nodes of Ranvier

(c)Remove myelination between nodes of Ranvier

(d)Decrease density of voltage-gated Na+ channels except at the Nodes of Ranvier

The resting membrane potential of a neuron can be estimated using the:

(a)Nernst equation

(b)Goldman equation

(c)Hodgkin and Huxley equation

(d)Ohmâs law

18. What would happen to the resting membrane potential of a neuron if you added K+ to the extracellular fluid?

(a)Resting membrane potential would increase (become more positive)

(b)Resting membrane potential would decrease (become more negative)

(c)Resting membrane potential would not change

(d)Resting membrane potential would be abolished

. Which of the following statements is FALSE for Graded Potentials

(a)Magnitude changes with magnitude of triggering stimulus

(b)Magnitude decreases with distance from initial site

(c)Cannot be summed

(d)No refractory period

In the nervous system, the strength of the stimulus is coded into:

(a)The frequency of action potentials generated

(b)The amplitude of action potentials generated

(c)Both the frequency and amplitude of action potentials generated

(d)The duration of individual action potentials generated

Ion movement during both the depolarization and repolarization phases of an action potential are the result of:

(a)active transport pumps along the neuron membrane.

(b)diffusion of ions down their electrochemical concentration gradients.

(c)negative feedback loops.

(d)All of the above

At the peak of the action potential, the membrane potential is:

(a)Exactly at the Na+ equilibrium potential

(b)Greater (more positive) than the Na+ equilibrium potential

(c)Above 0 mV but less positive than the Na+ equilibrium potential

(d)0 mV

KINESIOL 1Y03 Lecture Notes - Lecture 15: Saltatory Conduction, Neuroglia, Neurotransmission

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