Lecture 18

Question 1

What is the basis for the establishment and maintenance of the resting membrane potential?

Answer 1

The resting membrane potential is maintained by the sodium-potassium ATPase and leak channels, which create a charge difference across the membrane of approximately -70 mV.

Question 2

Describe three types of gated ion channels associated with neurons.

Answer 2

• Chemical gated channels
• Voltage gated channels
• Mechanically gated channels

Question 3

Define a local potential.

Answer 3

A local potential is a localized change in membrane voltage that occurs in response to a stimulus at a synapse.

Question 4

Describe how summation occurs at the axon hillock.

Answer 4

Summation occurs when multiple excitatory and inhibitory inputs combine to determine if an action potential is generated at the axon hillock.

Question 5

What neurotransmitter is used by a somatic efferent neuron?

Answer 5

Acetylcholine

Question 6

Which of the following is true about the sympathetic chain ganglia?
(a) The preganglionic neurons are unmyelinated
(b) They contain the axons of postganglionic neurons
(c) They contain cell bodies that utilize norepinephrine
(d) They contain cell bodies that give rise to myelinated axons

Answer 6

They contain the axons of postganglionic neurons

Question 7

If you were told that your craniosacral nervous system was activated, does that mean that you are:
(a) relaxed
(b) thoughtful
(c) hyperactive
(d) sympathetic

Answer 7

relaxed

Question 8

Which statement is true of a post-ganglionic parasympathetic neuron? (a) It is myelinated (b) It receives input from an unmyelinated axon (c) Its cell body resides distant from the CNS (d) Its cell body can be found in the collateral ganglion.

Answer 8

Its cell body resides distant from the CNS

Question 9

What is the role of the sodium-potassium ATPase in maintaining resting membrane potential?

Answer 9

It actively pumps 3 Na+ out of the cell and 2 K+ into the cell.

Question 10

What are leak channels and their function?

Answer 10

Leak channels are passive channels that allow K+ to flow out of the cell, contributing to the negative charge inside.

Question 11

What is the charge difference across the membrane at resting membrane potential?

Answer 11

Approximately -70 mV

Question 12

What activates chemical gated channels?

Answer 12

Chemicals such as neurotransmitters at a synapse

Question 13

What is the function of voltage gated channels?

Answer 13

They are essential for the generation and conduction of action potentials along the axon.

Question 14

How do mechanically gated channels operate?

Answer 14

They are activated by physical forces, such as pressure or deformation.

Question 15

What is an excitatory local potential?

Answer 15

A depolarization that makes the membrane potential more positive, typically caused by Na+ flowing into the cell.

Question 16

What is an inhibitory local potential?

Answer 16

A hyperpolarization that makes the membrane potential more negative, often caused by K+ flowing out of the cell.

Question 17

What is temporal summation?

Answer 17

When local potentials arrive close together in time, their effects add together.

Question 18

What is spatial summation?

Answer 18

When local potentials occur close together spatially on the neuron’s dendrites, allowing their effects to combine.

Question 19

What must occur at the axon hillock for an action potential to fire?

Answer 19

The net voltage change caused by local potentials must depolarize the membrane sufficiently to reach threshold (~10mV).

Question 20

What is the absolute refractory period?

Answer 20

A period during which a neuron cannot fire another action potential.

Question 21

What is the relative refractory period?

Answer 21

A period during which a larger-than-normal stimulus is required to generate an action potential.

Question 22

How is an action potential propagated along an axon?

Answer 22

The action potential in one segment activates the next segment through active propagation via voltage gated channels.

Question 23

What is the difference in action potential propagation between myelinated and unmyelinated axons?

Answer 23

Myelinated axons propagate action potentials faster due to insulation and fewer required action potentials at the nodes.

Question 24

What is the role of the Nodes of Ranvier in myelinated axons?

Answer 24

They are gaps that allow for rapid depolarization and concentration of voltage gated Na+ channels.

Question 25

Fill in the blank: The resting membrane potential is maintained by the _______.

Answer 25

sodium-potassium ATPase

Question 26

Fill in the blank: Local potentials can be either _______ or _______.

Answer 26

excitatory, inhibitory

Question 27

Why is myelination faster?

Answer 27

Myelin sheath acts like insulation around the axon, preventing ion movement across the membrane except at Nodes of Ranvier. ## Footnote Myelination allows fewer action potentials to be generated along the axon, concentrating Voltage Gated Na+ Channels at Nodes of Ranvier for rapid depolarization.

Question 28

What are the types of ion channels?

Answer 28

Chemical, voltage, and mechanically gated ion channels. ## Footnote Chemically gated channels are important for action potentials at the input zone, while voltage gated channels are crucial for propagation and transmission.

Question 29

What is a local potential?

Answer 29

Local changes in membrane voltage at the site of input (synapse) that are not propagated. ## Footnote Local potentials can be excitatory or inhibitory and can summate if they arise close together in space and time.

Question 30

What is an action potential?

Answer 30

A 2-3msec reversal in membrane polarity when threshold is reached at the axon hillock, characterized by Na+ entry for depolarization and K+ exit for repolarization. ## Footnote Action potentials are all-or-none and do not vary in size.

Question 31

What prevents backward propagation of action potentials?

Answer 31

Refractory periods. ## Footnote The absolute refractory period prevents any action potential from being generated, while the relative refractory period requires a very large stimulus.

Question 32

What is the absolute refractory period?

Answer 32

A period during which no action potential can be generated due to the inactivation gate of Voltage Gated Sodium Channels. ## Footnote This ensures that action potentials only propagate in one direction.

Question 33

What is the relative refractory period?

Answer 33

A period where a very large stimulus is required to generate an action potential, as the membrane is still repolarizing. ## Footnote More input is needed to reach the threshold during this period.

Question 34

What increases conduction velocity in axons?

Answer 34

Myelination. ## Footnote Myelination can increase conduction velocity up to 20-100m/sec by preventing leakage of local currents.

Question 35

What cells myelinate axons in the PNS?

Answer 35

Schwann Cells. ## Footnote In the CNS, axons are myelinated by oligodendrocytes.

Question 36

Ion channels on the cell body and dendrites of a neuron are typically:

Answer 36

A) Chemically-gated ## Footnote This type of channel is crucial for the generation of action potentials at the input zone.

Question 37

The site of initiation of the action potential is the:

Answer 37

C) Initial segment ## Footnote This is where the voltage-gated sodium channels open to begin the action potential.

Question 38

Which statement regarding action potentials is NOT true?

Answer 38

D) A large stimulus may initiate an action potential during the absolute refractory period. ## Footnote During the absolute refractory period, no action potential can be initiated.