Chapter 48: Neurons, Synapses, & Signaling (Mastering Biology & Dynamic Study Module)

At location _____, the voltage-gated Na+ channels reactivate.

A

Which type of transmembrane protein is directly responsible for maintaining the propagation of action potentials across an axon once it has been initiated?

Voltage-gated sodium channels

An action potential moves along a(n) _____.

Axon

"Saltatory conduction" means that the membrane potential changes __________.

Only at the nodes of Ranvier

At location _____, the voltage-gated K+ channels are closing.

B

Glial cells function in which of the following roles?

- Regulating extracellular fluid around some neurons - Transmitting signals - Insulating axons of neurons - Nourishing neurons ALL OF THE LISTED RESPONSES ARE CORRECT

A neuron has a resting potential of about _____ millivolts.

-70

Which of the following is a typical resting potential of a neuron?

-70 mV

Drag the labels onto the table to indicate which type(s) of gated ion channels are found in each membrane associated with a chemical synapse. (The letters in the table refer to the lettered structures in the image above.) Labels can be used once, more than once, or not at all.

A. Synaptic terminal: Voltage-gated Na+, Voltage-gated K+ B. Presynaptic membrane: Voltage-gated Na+, Voltage-gated K+, Voltage-gated Ca2+ C. Postsynaptic membrane: Ligand-gated D. Plasma membrane of cell body: None E. Axon hilock: Voltage-gated Na+, Voltage-gated K+

Drag the arrows onto the diagram to show the direction of Na+ (gray arrows) and K+ (red arrows) movement through each transport protein at resting potential. If no ions move through a transport protein at resting potential, leave that target blank.

A: Blank (resting potential) B: Blank (resting potential) C: Na+ out, K+ in D: K+ out E: Na+ in

Drag the labels onto the flowchart to indicate the sequence of events that occurs in the presynaptic cell (orange background) and the postsynaptic cell (blue background) after an action potential reaches a chemical synapse.

A: Ca2+ channels in presynaptic membrane open briefly B: Ca2+ ions enter the presynaptic cell C: Neurotransmitter-containing vesicles fuse with presynaptic membrane D: Neurotransmitter released into presynaptic cleft E: Neurotransmitter binds to ligand-gated ion channels in postsynaptic membrane; channels open F: Neurotransmitter degraded or removed from cleft; ligand-gated ion channels close

Drag the labels to their appropriate locations on the diagram of the neurons below. Use only the pink labels for the pink targets (which indicate the locations of gated ion channels).

A: Cell body B: Myelin sheath C: Synaptic terminal D: Axon hillock E: Nucleus F: Location of voltage-gated channels G: Location of ligans-gated channels H: Axon I: Dendrite

Drag the labels onto the graph to indicate which presynaptic neuron produced each change in the axon hillock's membrane potential. Assume that the same number of ligand-gated ion channels opens at each synapse. (To review the effect of distance between the synapse and the axon hillock, see Hint 2.) Labels can be used once, more than once, or not at all.

A: I2 B: E2 C: E1 D: I1 E: E2 F: E1

Drag the labels onto the flowchart to show the sequence of events that occurs once the membrane potential reaches threshold. You may use a label once or not at all

A: Many voltage-gated Na+ channels open B: Na+ ions rush into the cell C: Membrane potential rises

Drag the appropriate labels onto the graph to indicate the status (open or closed) of the voltage-gated Na+ and K+ channels during each phase of an action potential. Labels may be used once, more than once, or not at all.

A: Na+ channels closed, K+ channels closed B: Na+ channels open, K+ channels closed C: Na+ channels closed, K+ channels open D: Na+ channels closed, K+ channels open E: Na+ channels closed, K+ channels closed

Which term describes an electrical signal generated by neurons?

Action potential

Action potentials differ from graded potentials in that __________.

Action potentials are all of the same magnitude

An action potential moves along an axon due to the sequential opening of voltage-gated Na+ channels. The diagram below shows voltage-gated Na+ channels separated by a short distance in the plasma membrane of an axon. Initially (left panel), only channel (a) is open. Within a very short time (right panel), channel (b) also opens. Which statement correctly describes what causes the second voltage-gated Na+ channel to open?

After the first channel opens, the movement of many types of ions (both inside and outside the cell) alters the distribution of charges near the second channel, causing it to open

A nerve impulse moves away from a neuron's cell body along _____.

Axon

The interplay of multiple excitatory and inhibitory inputs most affects what part of a neuron?

Axon hillock

Where in the neuron do action potentials begin?

Axon hillock

How are neurons structurally adapted to chemically transmit impulses to neighboring neurons?

Axon terminals contain neurotransmitters within synaptic vesicles.

In the diagram, (a), (b), and (c) represent three points along a vertebrate axon where electrodes were implanted to detect action potentials. Under normal conditions, when this neuron produces an action potential, the action potential passes through point (a) first, followed by point (b), and then point (c). Enter the sequence in which the action potential would pass through the points. Enter the letters in the correct order separated by commas. For example if the order is point (c), then (b), then (a), enter c, b, a. If the action potential would not pass though a point, do not include that point in your answer.

B, A, C

Why is an action potential an all-or-none response to stimuli?

Because voltage-gated ion channels open when membrane potential passes a particular level

If the membrane potential of a neuron decreases, the membrane potential _____.

Becomes less negative

At location _____, the membrane potential changes sign (from a positive value to a negative value) and the voltage-gated K+ channels are open.

C

How does the movement of K+ ions through the artificial channel affect the membrane potential?

Causes a hyperpolarization

A neuron's nucleus is located in its _____.

Cell body

Acetylcholinesterase is the enzyme that degrades acetylcholine. What effect on nerve transmission would occur following the administration of a chemical that inhibited acetylcholinesterase?

Continuous excitatory postsynaptic potentials would occur in the postsynaptic neuron.

At location _____, the voltage-gated Na+ channels are inactivating and the voltage-gated K+ channels are opening.

D

Blocking potassium ion channels in a mammalian cell membrane would __________.

Decrease the magnitude of the membrane potential

A nerve impulse moves toward a neuron's cell body along _____.

Dendrites

The "information receiving" section of a neuron is its _____.

Dendrites

The part(s) of a neuron that receive(s) signals is/are the ____________.

Dendrites

At location _____, the membrane potential changes sign (from a negative value to a positive value) and the voltage-gated Na+ channels are open.

E

Which of the following is a natural pain reliever?

Endorphins

Sort the phrases into the appropriate bins depending on which type of postsynaptic potential they describe. If a phrase describes both types of potentials, drag it to the "both" bin.

Excitatory Postsynaptic Potential (EPSP): - Depolarizes the postsynaptic membrane - Results from the movement of Na+ ions into the postsynaptic cell - Brings the postsynaptoc membrane potential closer to threshold Inhibitory Postsynaptic Potential (IPSP): - Hyperpolarizes the postsynaptic membrane - Moves the postsynaptic membrane potential farther away from the threshold - Results from the movement of K+ ions out of the postsynaptic cell Both: - Is a graded potential

At location _____, the axon membrane reaches threshold and the voltage-gated Na+ channels open.

F

True or false? Action potentials travel in only one direction down an axon because potassium channels in the neuron are refractory and cannot be activated for a short time after they open and close.

False

True or false? The potential energy of a membrane potential comes solely from the difference in electrical charge across the membrane.

False

At location _____, the axon membrane is at resting potential.

G

Which of the following neurotransmitters typically has inhibitory effects?

GABA

The neurotransmitter nitric oxide (NO) ____________.

Has more than one target in the body

Which of the following characteristics determines when the refractory period ends?

How long it takes for the voltage-gated Na+ channels to reactivate at the end of an action potential

Which of the following terms describes how a neuronal membrane's potential is altered in the presence of inhibitory signals?

Hyperpolarization

Does the membrane potential promote or impede the movement of K+ ions through the artificial channel?

Impede

Which term describes the difference in electrical charge across a membrane?

Membrane potential

What causes the falling phase of the action potential? Select the best answer.

Inactivation of voltage-gated sodium channels and the opening of voltage-gated potassium channels

All else remaining constant, which of the following would constitute hyperpolarization of a neuron at rest?

Increasing Na+ outside of the cell

A drug that causes potassium to leak out of a neuron, increasing the positive charge on the outside, would __________.

Inhibit transmission of nerve signals by the neuron

Which of the following statements about the resting potential is true?

Inside the cell, the concentration of potassium is much higher than the concentration of sodium.

Which of the following is specifically a part or a function of the central nervous system?

Integration

Resting neurons are most permeable to which of the following ions?

K+

Axons insulated by a(n) _____ are able to conduct impulses faster than those not so insulated.

Myelin Sheath

Which structure is not part of a neuron?

Myelin sheath

Schwann cells make up the __________.

Myelin sheath in the PNS

What is the relationship between neurons and nerves?

Nerves are comprised of neurons.

An impulse relayed along a myelinated axon "jumps" from _____ to _____.

Node of Ranvier...Node of Ranvier

The transmission first triggers the _____.

Opening of voltage-gated sodium channels and the diffusion of sodium ions into the neuron

In what direction will the K+ ions move through the artificial channel?

Out of the cell

Threshold is of great significance in the physiology of neurons because if threshold is not reached, __________.

Positive-feedback depolarization will not occur

Where would a ligand-gated ion channel typically be found on a neuron?

Postsynaptic membrane

Which channel is mainly responsible for the resting potential of a neuron?

Potassium leak channel

In descriptions of synapse organization, the __________ cell is the transmitting neuron and the __________ is the neuron, muscle, or gland cell that receives the signal.

Presynaptic...Postsynaptic

Does the K+ concentration gradient promote or impede the movement of K+ ions through the artificial channel?

Promote

What is the relationship between membrane potential and resting potential?

Resting potential is the membrane potential of a neuron that is at rest.

What type of cell makes up the myelin sheath of a motor neuron?

Schwann cells

A neuron that transmits an impulse to the central nervous system after the neuron is stimulated by the environment is called a(n) __________.

Sensory neuron

There are two properties that affect the conduction speed of an action potential along an axon: the axon's diameter and whether or not the axon is myelinated. Rank the axons from slowest to fastest conduction speed. If two axons have the same conduction speed, place one on top of the other.

Slowest - Non-myleinated invertebrate axon 20 um diameter - Non-myleinated invertebrate axon 30um diameter - Non-mylelinated invertebrate axon 40 um diameter - Myelinated vertebrate axon (with bubbles) 30um diameter Fastest

In a neuron, ion channels permit movement of (but don't pump) ____________.

Sodium (Na+) and potassium (K+)

Sodium-potassium pumps transport ___________.

Sodium ions (Na+) out of a neuron and potassium ions (K+) into a neuron

How is an action potential propagated down an axon after voltage-gated sodium channels open in a region of the neuron's membrane?

Sodium ions enter the neuron and diffuse to adjacent areas, resulting in the opening of voltage-gated sodium channels farther down the axon

A stimulus has opened the voltage-gated sodium channels in an area of a neuron's plasma membrane. As a result, _____ rushes into the neuron and diffuses to adjacent areas; this in turn results in the _____ in the adjacent areas.

Sodium...Opening of voltage-gated sodium channels

Which of the following statements is an accurate description of neurotransmitters?

Some neurotransmitters can bind to multiple different types of receptors.

What part of a neuron relays signals from one neuron to another neuron or to an effector?

Synaptic terminal

The equilibrium potential for a particular ion is __________.

The magnitude of the membrane voltage at equilibrium for that ion

Which event triggers the creation of an action potential?

The membrane depolarizes above a certain threshold potential

What governs the opening of the potassium channels, which establish the resting membrane potential in the plasma membrane of a neuron?

The potassium channels are always open.

The period in which an axon membrane cannot act is called __________.

The refractory period

What behavior is observed if the voltage across a neuronal membrane is set to -20 mV?

The sodium channel opens, and Na+ ions flow in

Which channel maintains the concentration gradients of ions across a neuronal membrane?

The sodium-potassium pump moving Na+ ions out and K+ ions in

At rest, which of these plays a role in establishing the charge differential across a neuron's plasma membrane?

The sodium-potassium pump moving sodium ions out of the neuron and potassium ions into the neuron

Which of the following statements about action potentials in a given neuron is false?

They are propagated down the length of the dendrite

Ions move in the direction opposite to that favored by the chemical concentration gradient when _____.

They are pumped by proteins that require ATP hydrolysis and when the electrical charge gradient repulses or attracts them