Problem Set 5: Neurophysiology - Cellular Networks

Match the part of the neuron to its description. A. dendrites B. axon C. cell body occupy(ies) the least amount of cell volume

cell body

Drag and drop each of the terms at the left to the correct statement at the right.

Depolarization: Sodium ions are moving in, and the membrane potential is becoming less negative than the resting membrane potential. Repolarization: Potassium ions are moving out, and the membrane potential is becoming more negative as it moves back toward the resting membrane potential. Hyperpolarization: Potassium ions are moving out, and the membrane potential is becoming more negative than the resting membrane potential.

Which of the following neurons or groups of neurons is NOT considered to be a part of the efferent pathway? Sympathetic Somatic motor Sensory Parasympathetic

Sensory

What event triggers the generation of an action potential?

The membrane potential must depolarize from the resting voltage of -70 mV to a threshold value of -55 mV.

What is the function of the myelin sheath?

The myelin sheath increases the speed of action potential conduction from the initial segment to the axon terminals.

Tetrodotoxin is a toxin that blocks voltage-gated sodium channels. What effect does this substance have on the function of neurons?

The neuron is not able to transmit action potentials.

The velocity of the action potential is fastest in which of the following axons?

a small myelinated axon

The mechanism by which the neurotransmitter is returned to a presynaptic neuron's axon terminal is specific for each neurotransmitter. Which of the following neurotransmitters is broken down by an enzyme before being returned?

acetylcholine

Glial cells communicate primarily using

chemical signals only.

Binding of a neurotransmitter to its receptors opens __________ channels on the __________ membrane.

chemically gated; postsynaptic

Which of the following statements best describes the resting membrane potential? Choose the best answer.

an electrical gradient that exists between the intracellular and extracellular fluids

During an action potential, when does sodium ion permeability begin to significantly decline?

at the peak of depolarization

Where in the neuron is an action potential initially generated?

axon hillock

Match the part of the neuron to its description. A. dendrites B. axon C. cell body receive(s) most of the incoming synapses

dendrites

An action potential is self-regenerating because __________.

depolarizing currents established by the influx of Na+‎ flow down the axon and trigger an action potential at the next segment

Binding of the neurotransmitter to its receptor causes the membrane to __________.

either depolarize or hyperpolarize

A molecule that carries information across a synaptic cleft is a

neurotransmitter

Match the term with its description. A. ependymal cells B. astrocytes C. satellite cells D. schwann cells E. oligodendrocytes F. microglia cells in the CNS that form myelin

oligodendrocytes

In a synapse, neurotransmitters are stored in vesicles located in the __________.

presynaptic neuron

The portions of a neuron that extend off of the roughly spherical cell body are usually collectively called

processes

Hyperpolarization results from __________.

slow closing of voltage-gated K+ channels

The channelopathy known as Q-T syndrome is a result of mutation in ________ channels.

sodium, potassium, or calcium

During an action potential, the rapid decrease in sodium ion permeability and the simultaneous and rapid increase in potassium ion permeability is responsible for __________.

the repolarization phase

When calcium ions enter the synaptic terminal,

they cause vesicles containing neurotransmitter molecules to fuse to the plasma membrane of the sending neuron.

An action potential releases neurotransmitter from a neuron by opening which of the following channels?

voltage-gated Ca2+ channels

The depolarization phase of an action potential results from the opening of which channels?

voltage-gated Na+ channels

What stops the rising phase of the action potential?

The Na+ inactivation gate closes.

Why does the action potential only move away from the cell body?

The areas that have had the action potential are refractory to a new action potential.

What characterizes depolarization, the first phase of the action potential?

The membrane potential changes from a negative value to a positive value.

If a signal from a sending neuron makes the receiving neuron more negative inside,

the receiving neuron is less likely to generate an action potential.

The cell body of neurons is about

10% of the cell volume.

What is the magnitude (amplitude) of an action potential?

100 mV

How is an action potential propagated along an axon?

An influx of sodium ions from the current action potential depolarizes the adjacent area.

What type of conduction takes place in unmyelinated axons?

Continuous conduction

What changes occur to voltage-gated Na+ and K+ channels at the peak of depolarization?

Inactivation gates of voltage-gated Na+‎ channels close, while activation gates of voltage-gated K+‎ channels open.

Where do most action potentials originate?

Initial segment (axon hillock)

Sodium ions are more concentrated on the outside of the cell, this would result in diffusion of the ion into the cell.

Potassium ions are more concentrated on the inside of the cell, this would result in diffusion of the ion out of the cell.

In which type of axon will velocity of action potential conduction be the fastest?

Myelinated axons with the largest diameter

The rising phase of the action potential is due to

Na+ flow into the cell

What characterizes repolarization, the second phase of the action potential?

Once the membrane depolarizes to a peak value of +30 mV, it repolarizes to its negative resting value of -70 mV.

The afferent and efferent neurons together form the

PNS

During the relative refractory period, an initial threshold-level depolarization is usually not sufficient to initiate an action potential. Why?

Some Na+ channels have returned to their resting position and K+ channels are still open, so Na+ entry is offset by K+ loss.

Why does regeneration of the action potential occur in one direction, rather than in two directions?

The inactivation gates of voltage-gated Na+‎ channels close in the node, or segment, that has just fired an action potential.

What opens first in response to a threshold stimulus?

Voltage-gated Na+ channels

What is the first change to occur in response to a threshold stimulus?

Voltage-gated Na+ channels change shape, and their activation gates open.

Neurotransmitters are usually released into synapses by __________.

exocytosis

The neurotransmitter thought to be involved in learning and memory is

glutamate

Interneurons are found

in the CNS

The neurons of the central nervous system are also known as __________.

interneurons

When neurotransmitter molecules bind to receptors in the plasma membrane of the receiving neuron,

ion channels in the plasma membrane of the receiving neuron open.

In most cells, the concentration of ions contributing to the membrane potential is __________ in the intracellular fluid compared with the extracellular fluid, with the exception of __________ ions.

lower; potassium

A stronger stimulus to a neuron results in __________.

stronger graded potentials

The small space between the sending neuron and the receiving neuron is the

synaptic cleft

Which of the following statements best describes the concept of permeability? Choose the best answer.

the ability of a molecule to cross the cell membrane

Which statement is true when a neuron is at rest?

the activation gate is closed and the inactivation gate is open

The repolarization phase of an action potential results from __________.

the opening of voltage-gated K+ channels