Quiz #4 on Neurophysiology

Interactive Lecture Quiz #4 on Chapter 8– Neurophysiology

Spring, 2008By Patricia L. Mansfield, Ph.D.

Directions. Take this quiz using your powerpoint viewer to test yourself and to get immediate feedback on your answer choice.

I obtained some animations or videos from internet classes or from your textbook author to demonstrate the important principles covered in this quiz.

13/17/2008

Let’s review some of the facts you learned when you studied the “Transmembrane Potential” and add a few facts to this knowledge base.

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• The selective permeability of the cell membrane controls the concentration of positive and negative ions in the ICF and ECF.

• Some sodium ions diffuse into the cell through leaky channels; some potassium diffuses out of the cell through channels that are always open.

• The sodium-potassium pump maintains a balance between the ICF and ECF concentrations of sodium and potassium such that

[Sodium]ICF < [Sodium]ECF and [Potassium]ICF > [Potassium]ECF.• This membrane system pumps 3 sodium ions out of the cell for every 2

potassium ions pumped into the cell.• Anions trapped inside cells explain the negative value of the “resting

membrane potential”.• The “resting membrane potential” is most sensitive to changes in the

potassium ion concentration outside the cell.• In excitable cells, the “membrane potential” shifts away from the

“resting” value depending upon the level of stimulation of the cell.• One very important mechanism for this change is that closed, gated

channels open under certain conditions –when a signal molecule is present– and more ions move into the cell.

Apply the facts in the first slide to neurons.

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• Potassium channels are both gated and ungated in neurons.

• Sodium channels are always gated and rarely leaky. • Gated channels open only when the cell is stimulated. • -70mV is a normal resting membrane potential for many

CNS neurons. However, this value can vary from –60mV to –90mV depending upon the characteristics of the particular neuron being studied.

1. Children who could not move their muscles could feelpain. Which part of the nervous system has been damaged?a. afferent axons b. efferent axons c. brain d. sympathetic

Afferent axons – Conduct an action potential when a receptor acts as a

transducer Carry sensory information into the CNS

Efferent axons – Conduct an action potential when a signal molecule is

released from another CNS neuron Carry motor information to an effector, for example

skeletal muscle

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Identify the afferent and efferent sides of this reflex arc:http://ext.sac.edu/faculty_staff/mansfield_patricia/Animations/reflex_arc.html

2. Sodium ions enter a neuron during an action potential. Which type of feedback is demonstrated in this response?a. negative b.positive c. neither

Physical Factors behind the Action Potential http://psych.hanover.edu/krantz/neural/actionpotential.html

Uncovering misconceptions about the resting membrane potential by Dee Silverthorn, 2002 http://advan.physiology.org/cgi/content/full/26/2/69

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3. Most synapses are classified as _____.a. electrical b. chemical c. multimodal d. continuous

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Silverthorn, Figure 8-19, A Chemical Synapse

Synapse Mechanism: Signal (Neurotransmitter) – Receptor Binding

Figure 8-20: Events at the synapse

4. Saltatory conduction occurs in _____.a. astrocytes b. microglia c. myelinated axons d. unmyelinated axons

5. What is (directly) responsible for the ion movement that creates an action potential?a. voltage-gated ion channels b. chemically-gated ion channelsc. ungated channels d. mechanically-gated ion channels

This CNS multipolar neuron has chemically-regulated gates on its dendrites and cell body--#1, #3, and #4.The voltage-regulated gates on the axon hillock are indicated by #2. This is the area responsible for generating the action

potential.

6. How does an action potential (AP) differ from an EPSP (excitatory postsynaptic potential)?a. During an AP, the membrane potential becomes more positive.b. During an AP, sodium ions move into the cell.c. An AP is an all-or-none event.d. An AP is an electrical signal.

EPSP IPSP ACTION POTENTIAL (AP)

Electrical signal Electrical signal Electrical signal

Generated at chemically-regulated gates

Generated at chemically-regulated gates

Generated at voltage-regulated gates

Generated at dendrites or neuron cell bodies

Generated at neuron cell bodies

Generated at the axon hillock

Requires an influx of Na+ ions Requires an influx of Cl- ions Requires an influx of Na+ ions followed by an efflux of K+ ions

No threshold No threshold Threshold

Graded potential Graded potential All-or-none potential

No refractory period No refractory period Absolute and Relative refractory periods

Capable of summation Capable of summation All-or-none potential

May trigger an AP Will not trigger an AP Not applicable

Silverthorn, Figure 8-7: Graded potentials decrease in strength as they spread out from the point of origin

Silverthorn, Figure 8-9: The action potential

Silverthorn, Figure 8-10: Model of the voltage-gated channel Na+

6. How does an action potential (AP) differ from an EPSP (excitatory postsynaptic potential)?a. During an AP, the membrane potential becomes more positive.b. During an AP, sodium ions move into the cell.c. An AP is an all-or-none event.d. An AP is an electrical signal.

Neuron #1 has a resting membrane potential of -70mV and a threshold of -50mV. A threshold stimulus is a stimulus that moves the

membrane potential _____ . If I apply a stimulus that moves the membrane potential

+40mV, I will get an ____ as soon as the membrane potential reaches ____ .

If I apply a stimulus that moves the membrane potential +10mV, I will get an ____ , but no ____

7. Which of the following is a gas? a. CCKlb. aspartate c. nitric oxide d. serotonin

Review the list of the major neurotranmitters of the NS in your syllabus

Know the key facts concerning their biosynthetic pathways, mechanism for degradation, and pharmacology

8. Which ion will hyperpolarize the membrane when it moves into a neuron?a. Na+ b. K+ c. Cl-d. GABA

Neurocrines

Table 8-4-2: Major Neurocrines

9. When can a greater than normal stimulus (suprathreshold stimulus) trigger an AP?a. during the absolute refractory periodb. when the neuron is at restc. during the relative refractory period d. a and c e. b and c

Neuron #1 has a resting membrane potential of -70mV and a threshold of -50mV. A threshold stimulus is a stimulus that moves the

membrane potential _____ . If I apply a stimulus that moves the membrane potential

+40mV, I will get an ____ as soon as the membrane potential reaches ____ .

If I apply a stimulus that moves the membrane potential +10mV, I will get an ____ , but no ____ .

10. Which of the following is an inhibitory neurotransmitter?a. aspartate b. glutamate c. ACh d. GABA

11. What event will the application of an inhibitory neurotransmitter trigger?a. AP b. EPSP c. IPSP d. influx of Na+ ions

Neuron #2 has a resting membrane potential of -70mV, a threshold of -50mV and a membrane potential of -80mV after a hyperpolarizing stimulus was delivered. If I apply a threshold stimulus under these conditions, I will

get an _____ , but no ____ because the positive change of ____ caused by the threshold stimulus is not sufficient to bring the membrane potential to -50mV.

I need a stimulus sufficient to produce a ____ change in the membrane potential to get an action potential.

Answers 1. B 2. B 3. B 4. C 5. A 6. C 7. C 8. C 9. E 10. D 11. C

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