Chp 12

In order to communicate with multiple cells at the same time, an axon may branch along its length, producing side branches called __________. axon terminal collaterals telodendria initial segment

collaterals

Rabies illustrates a negative consequence to otherwise healthy retrograde flow within axons. Which of the following components will NOT be involved in retrograde flow? axoplasm kinesin axon hillock neuronal cell body

kinesin

Which of these neurotransmitters is released at CNS adrenergic synapses? serotonin GABA norepinephrine adrenaline

norepinephrine

The movement of what ion is responsible for the local currents that depolarize other regions of the axon to threshold?

sodium (Na+)

What type of conduction takes place in unmyelinated axons? Synaptic transmission Electrical conduction Continuous conduction Saltatory conduction

Continuous conduction

Know all about action potential.

During the repolarization phase, sodium channels close and potassium channels open. During the depolarization phase, membrane potential becomes positive. During the hyperpolarization phase, the ion pumps re-establish the sodium and potassium concentrations across the cell membrane. Repolarization occurs as potassium ions leave the axon.

Neuroglia perform all of these functions EXCEPT __________. release neurotransmitters provide supportive framework regulate extracellular fluid composition secrete CSF

Except release neurotransmitters

Where do most action potentials originate?

Initial segment

Sodium and potassium ions can diffuse across the plasma membranes of all cells because of the presence of what type of channel? Ligand-gated channels Voltage-gated channels Leak channels Sodium-potassium ATPases

Leak channels

What ion is responsible for the depolarization of the neuron during an action potential?

Na+ (sodium)

The concentrations of which two ions are highest outside the cell.

Na+ and Cl-

What happens during repolarization of a neuron?

Na+ channels close and K+ channels open, lowering the voltage back down toward -70 mv to -90 mv. The resting membrane potential is in the process of being restored, but concentrations of sodium and potassium are not back to their original state. During relative refraction, the electrical state of resting potential is restored, but the chemical conditions are not. This makes generation of another action potential less likely, but not impossible.

The Na+-K+ pump actively transports both sodium and potassium ions across the membrane to compensate for their constant leakage. In which direction is each ion pumped?

Na+ is pumped out of the cell and K+ is pumped into the cell.

What prevents the Na+ and K+ gradients from dissipating?

Na+-K+ ATPase

Temporal summation

One or more presynaptic neurons transmit impulses in rapid-fire order

How do action potential propagation speeds in myelinated and unmyelinated axons compare?

Propagation is faster in myelinated axons.

Ions are unequally distributed across the plasma membrane of all cells. This ion distribution creates an electrical potential difference across the membrane. What is the name given to this potential difference? Action potential Positive membrane potential Resting membrane potential (RMP) Threshold potential

Resting membrane potential (RMP)

What are the functions of the neuroglia?

Support, secretion of cerebrospinal fluid, maintenance of blood-brain barrier, phagocytosis

On average, the resting membrane potential is -70 mV. What does the sign and magnitude of this value tell you?

The inside surface of the plasma membrane is much more negatively charged than the outside surface.

Josh and a bunch of friends decided to see how many people they could squeeze into a small car for a charity event. Once inside, Josh felt it get hot, smelly, and like the air was getting squished out of his lungs. He also noticed aches and pains in his joints. Which of the following statements best describes the type of sensory neurons involved?

The interoceptors, exteroceptors, and proprioceptors were all monitoring his condition.

At rest, why is the transmembrane potential of a neuron (-70 mV) closer to the potassium equilibrium potential (-90 mV) than it is to the sodium equilibrium potential (+66 mV)?

The membrane is much more permeable to potassium ions than to sodium ions.

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

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

The resting membrane potential depends on two factors that influence the magnitude and direction of Na+ and K+ diffusion across the plasma membrane. Identify these two factors.

The presence of concentration gradients and leak channels

In an unmyelinated axon, why doesn't the action potential suddenly "double back" and start propagating in the opposite direction?

The previous axonal segment is refractory

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.

During an action potential, after the membrane potential reaches +30 mV, which event(s) primarily affect(s) the membrane potential?

Voltage-gated sodium channels begin to inactivate (close) and voltage-gated potassium channels begin to open.

What happens just after an axon is depolarized to threshold? Chemically-gated sodium channels open. Voltage-gated sodium channels open. Some potassium channels open. All potassium channels open.

Voltage-gated sodium channels open.

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? glutamate acetylcholine

acetylcholine

Which division of the PNS would contain sensory nerve fibers from special sensory receptors? efferent sympathetic afferent parasympathetic

afferent

What most directly causes the exocytosis of Ach in synaptic vesicles?

arrival of calcium ions in the axon terminal

When a person has a stroke, blood leaks into the brain tissue. Which type of neuroglia cells would make structural repairs to the damage? ependymal cells oligodendrocytes satellite cells astrocytes

astrocytes

The simplest level of information processing takes place at the __________. axon hillock axon terminals dendrites soma

axon hillock

Resynthesis of ACh occurs in the __________. axon cell body axon terminal synapse

axon terminal

During depolarization, which gradient(s) move(s) Na+ into the cell?

both the electrical and chemical gradients

Which ion triggers synaptic vesicles to discharge neurotransmitter into the synaptic cleft?

calcium

The afferent division of the PNS __________. carries sensory information controls skeletal muscle carries motor commands controls smooth muscle

carries sensory information

Typical CNS neurons are amitotic due to the absence of what structure? ribosomes axons dendrites centrioles

centrioles

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

chemically gated; postsynaptic

In contrast to the internodes of a myelinated axon, the nodes __________.

have lower membrane resistance to ion movement

Action potential propagation begins (is first generated at) what region of a neuron?

initial segment

In what part of the neuron does the action potential typically initiate?

initial segment of the axon

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.

If a nerve cell receives many IPSPs in different locations at the same time, __________. the membrane potential will depolarize the nerve cell will approach threshold it will show spatial summation

it will show spatial summation

Most CNS neurons fall into which structural category? unipolar multipolar anaxonic bipolar

multipolar

Hyperpolarization results from __________.

slow closing of voltage-gated K+ channels

The repolarization phase of an action potential results from __________.

the opening of voltage-gated K+ channels

In a neuron, sodium and potassium concentrations are maintained by the sodium-potassium exchange pump such that __________.

the sodium concentration is higher outside the cell than inside the cell and the potassium concentration is higher inside the cell than outside the cell.

What is the electrochemical gradient of an ion?

the sum of the electrical and chemical gradients for that ion

During an action potential of a neuron, what directly causes the different channels to open and close? calcium ions neurotransmitter binding to chemically gated channels Sodium and potassium ions the transmembrane potential (voltage)

the transmembrane potential (voltage)

When calcium ions enter the synaptic terminal,

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

In a typical neuron, what is the equilibrium potential for sodium?

+66mV

Around what transmembrane potential does threshold commonly occur? -70 mV +60 mV -60 V -60 mV

-60 mV

In a typical neuron, what is the equilibrium potential for potassium?

-90 mV

What is a neuron that receives a neurotransmitter from another neuron called?

A postsynaptic neuron.

What happens when sodium channels in the axon membrane are opened?

A rapid influx of Na+ into the cell occurs, raising the voltage from -70 mv toward +30mv (an amplitude of 100). Once the membrane reaches a threshold of -50mv an action potential is initiated.

Compared to type A axons, type C axons are __________. unmyelinated smaller diameter slower propagating All of the listed responses are correct

All of the listed responses are correct

During propagation of the action potential, __________. the axon hillock depolarizes the initial segment local currents depolarize a spot adjacent to the active zone after threshold is reached, voltage-gated sodium channels open rapidly All of the listed responses are correct

All of the listed responses are correct

Identify the sequence of events that occurs at a synapse

An action potential arrives at the synaptic terminal. Calcium channels open, and calcium ions enter the synaptic terminal. Vesicles containing neurotransmitter fuse with the plasma membrane of the sending neuron. Neurotransmitter molecules diffuse across the synaptic cleft. The neurotransmitter molecules bind to receptors in the plasma membrane of the receiving neuron, causing ion channels there to open.

The sodium-potassium exchange pump stabilizes resting potential of the neuron membrane at about __________. +66 mV -90 mV -70 mV -20 mV

-70 mV

Approximately how fast do action potentials propagate in unmyelinated axons in humans?

1 meter per second

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

100 mV

What is the typical duration of a nerve action potential?

2 ms

Put the following steps involved in transmission at a cholinergic synapse in order. 1. Chemically-gated sodium channels on the postsynaptic membrane are activated. 2. Calcium ions enter the synaptic terminal. 3. Acetylcholinesterase hydrolyzes acetylcholine. 4. An action potential depolarizes the synaptic terminal at the presynaptic membrane. 5. The synaptic terminal reabsorbs choline. 6. Acetylcholine is released from storage vesicles by exocytosis. 7. Acetylcholine binds to receptors on the postsynaptic membrane. 8. Calcium ions are removed from the cytoplasm of the synaptic terminal.

4, 2, 6, 7, 1, 8, 3, 5

Put the following main steps in the generation of an action potential in order. 1. Sodium channels are inactivated. 2. Voltage-gated potassium channels open and potassium moves out of the cell, initiating repolarization. 3. Sodium channels regain their normal properties. 4. A graded depolarization brings an area of an excitable membrane to threshold. 5. A temporary hyperpolarization occurs. 6. Sodium channel activation occurs. 7. Sodium ions enter the cell and depolarization occurs.

4, 6, 7, 1, 2, 3, 5

How is an action potential propagated along an axon?

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

The neurotransmitter glutamate opens channels that are permeable to sodium ions. What effect does glutamate produce on a postsynaptic neuron? EPSPs neither IPSPs nor EPSPs IPSPs both IPSPs and EPSPs

EPSPs

In which cell does a graded potential occur? adipocytes epithelial cells neurons Graded potentials occur in all the cell types listed.

Graded potentials occur in all the cell types listed.

Know all about glial cells.

In the CNS there are astrocytes, ependymal cells, microglia, and oligodendrocytes In the PNS there are satellite cells and Schwann cells See picture above for details on the different glial cell functions

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.

What ion causes repolarization of the neuron during an action potential?

K+ (potassium)

What are the functions of the astrocytes?

Maintain the blood brain barrier Provide structural support Regulate ion, nutrient, and dissolved gas concentrations Absorb and recycle neurotransmitters Form scar tissue after injury

In which type of axon will velocity of action potential conduction be the fastest? Unmyelinated axons of the shortest length Unmyelinated axons with the largest diameter Myelinated axons with the largest diameter Myelinated axons with the smallest diameters

Myelinated axons with the largest diameter

Which of these neurotransmitters does NOT bind to a plasma membrane receptor? serotonin GABA nitric oxide norepinephrine

NOT nitric oxide

What characterizes repolarization, the second phase of the action potential? Once the membrane depolarizes to a threshold value of approximately -55 mV, it repolarizes to its resting value of -70 mV. Once the membrane depolarizes to a peak value of +30 mV, it repolarizes to its negative resting value of -70 mV. As the membrane repolarizes to a negative value, it goes beyond the resting state to a value of -80 mV. Before the membrane has a chance to reach a positive voltage, it repolarizes to its negative resting value of approximately -70 mV.

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

Know all about the sodium-potassium ion exchange pump.

Requires ATP. Pushes three Na+ ions out of the cell, and two K+ ions into the cell. This is against the cell's NA+ and K+ concentration gradient and against the cell's K+ electrical gradient.

What are the types of glial cells found in the peripheral nervous system?

Satellite cells - regulate the area Shwan cells - myelinate the peripheral neurons

What are the functions of the nervous system?

Sense the internal and external environments, integrate sensory information, coordinate voluntary and involuntary activities, control peripheral effectors

The sodium-potassium exchange pump transports potassium and sodium ions in which direction(s)?

Sodium ions are transported out of the cell. Potassium ions are transported into the cell. The energy of ATP is used to actively transport potassium and sodium ions against their electrochemical gradients. Potassium and sodium ions diffuse in the opposite direction through channels.

When you take a pain reliever, which of the following best describes, in general terms, how this affects the threshold of neurons? Taking a pain reliever increases the threshold. Taking a pain reliever decreases the threshold. Taking a pain reliever affects the all-or-none principle of neurons. So, neurons reaching threshold send an action potential at 50%. Taking a pain reliever does not affect the threshold of neurons.

Taking a pain reliever increases the threshold.

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.

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 event triggers the generation of an action potential? The membrane potential must hyperpolarize from the resting voltage of -70 mV to the more negative value of -80 mV. The membrane potential must depolarize from the resting voltage of -70 mV to its peak value of +30 mV. The membrane potential must return to its resting value of -70 mV from the hyperpolarized value of -80 mV. The membrane potential must depolarize from the resting voltage of -70 mV to a threshold value of -55 mV.

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.

Spatial summation

The sum of multiple synapses firing at different locations at one time to create a net effect.

The plasma membrane is much more permeable to K+ than to Na+. Why?

There are many more K+ leak channels than Na+ leak channels in the plasma membrane.

Female gymnasts can contort their bodies in many different ways and land on a 4" beam with accuracy. Which fiber type is responsible for this ability? Type A fibers Type B fibers Type C Type D fibers

Type A fibers

What is threshold stimulus?

Voltage needed to promote an action potential, usually -55 mv.

Multiple sclerosis (MS) is a disease that stops action potential propagation by destroying the myelin around (normally) myelinated axons. Which of the following best describes how MS stops action potential propagation? Without myelin, the internode membrane resistance decreases, preventing local currents from reaching adjacent nodes. Without myelin, the internode membrane is depolarized more easily. Without myelin, the internode membrane resistance increases, preventing local currents from reaching adjacent nodes. Without myelin, the node membrane more easily becomes refractory.

Without myelin, the internode membrane resistance decreases, preventing local currents from reaching adjacent nodes.

The electrochemical gradient for potassium ions when the transmembrane potential is at the resting potential (-70 mV) is caused by what?

a chemical gradient going out of the cell and an electrical gradient going into the cell

What are the structural classifications for neurons?

anaxonic, bipolar, unipolar, multipolar, Type A, Type B, and Type C

Where are action potentials regenerated as they propagate along an unmyelinated axon?

at every segment of the axon

Where are action potentials regenerated as they propagate along a myelinated axon? at myelin at the nodes at the internodes at every segment of the axon

at the nodes

When a neuron communicates with another at a synapse on a dendrite, this is called an __________ synapse. axosomatic axodendritic axoaxonic axoterminal

axodendritic

The electrochemical gradient for sodium ions in a neuron when the transmembrane potential is at the resting potential is caused by what?

chemical and electrical gradients both going into the cell

Leak channels allow the movement of potassium and sodium ions by what type of membrane transport? channel-mediated diffusion active transport simple diffusion facilitated diffusion

channel-mediated diffusion Ions move through leak channels because of chemical and electrical gradients

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 depolarize hyperpolarize

either depolarize or hyperpolarize

What type of membrane transport causes the depolarization phase of the action potential in neurons? filtration active transport facilitated diffusion simple diffusion

facilitated diffusion

If EPSPs summate to a sustained value above threshold, then the initial segment will __________. hyperpolarize generate larger than normal action potentials be inhibited generate a string of action potentials

generate a string of action potentials

Compared to the electrical gradient for sodium at rest, the electrical gradient for potassium at rest is __________. in the same direction but of lesser magnitude. in the opposite direction but of the same magnitude. in the same direction and of the same magnitude. in the same direction but of greater magnitude.

in the same direction and of the same magnitude. Because sodium and potassium each carry a single positive charge, the transmembrane potential affects them the same. The electrical gradient is entirely independent of the chemical gradient or the absolute concentrations of the ions.

Which type of ion channel is always open? mechanically-gated chemically-gated voltage-gated leak

leak (channel mediated diffusion)

A molecule that carries information across a synaptic cleft is a synaptic cleft. neurotransmitter. sending neuron. receiving neuron. synapse.

neurotransmitter.

What causes repolarization of the membrane potential during the action potential of a neuron? sodium influx (entering the cell) potassium influx (entering the cell) sodium efflux (leaving the cell) potassium efflux (leaving the cell)

potassium efflux (leaving the cell)

The most abundant intracellular cation is __________, while the most abundant extracellular anion is __________.

potassium, chloride

The neurotransmitter GABA blocks presynaptic voltage-gated calcium channels. Consequently, GABA produces __________. EPSPs presynaptic inhibition presynaptic facilitation IPSPs

presynaptic inhibition

In a synapse, neurotransmitters are stored in vesicles located in the __________. synaptic cleft postsynaptic neuron presynaptic neuron

presynaptic neuron

The node-to-node "jumping" regeneration of an action potential along a myelinated axon is called __________.

saltatory propagation

Which of these types of neuroglia are abundant in peripheral ganglia? astrocytes satellite cells microglia oligodendrocytes

satellite cells

Which of these substances is NOT considered a neuromodulator? opioids substance P endorphins enkephalins

substance P

The small space between the sending neuron and the receiving neuron is the synaptic terminal. calcium channel. synaptic cleft. neurotransmitter. vesicle.

synaptic cleft.

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.

An action potential releases neurotransmitter from a neuron by opening which of the following channels? chemically gated Ca2+ channels voltage-gated Ca2+ channels voltage-gated K+ channels voltage-gated Na+ channels

voltage-gated Ca2+ channels

What is primarily responsible for the brief hyperpolarization near the end of the action potential?

voltage-gated potassium channels taking some time to close in response to the negative membrane potential