Chapter 48 Practice

Which channel maintains the concentration gradients of ions across a neuronal membrane? a. the sodium-potassium pump moving Na+ ions our and K+ ions in b. the sodium-potassium pump moving Na+ ions in and K+ ions out c. the potassium leak channel allowing K+ ions out d. the sodium leak channel allowing NA+ ions out

a. the sodium-potassium pump moving Na+ ions out and K+ ions in

Resting neurons are most permeable to which of the following ions? a. K+ b. O-- c. Na+ d. Cl--

a. K+

A neuron's nucleus is located in its _____. a. cell body b. axon c. myelin sheath d. dendrite e. synaptic terminals

a. cell body

An action potential moves along a(n) ______. a. myelin sheath b. axon c. dendrite d. synapse e. cell body

b. axon

A neuron has a resting potential of about _____ mV. a. +50 b. +35 c. -55 d. -70 e. -80

d. -70

Effect of Multiple Synapses description

A single neuron can receive signals from many sending neurons. Two sets of signals - excitatory and inhibitory cancel each other out and no action potential is generated.

What type of cell makes up the myelin sheath of a motor neuron? a. astrocytes b. microglial cells c. Ranvier cells d. ependymal cells e. Schwann cells

e. Schwann cells Myelin sheaths are formed when Schwann cells wrap around the axons of motor neurons

Where is the neuron do action potentials begin? a. axon hillock b. synapse c. cell body d. dendrite

a. axon hillock

Which channel is mainly responsible for the resting potential of a neuron? a. voltage gated potassium channel b. chloride leak channel c. voltage gated sodium channel d. potassium leak channel

d. Potassium leak channel K+ ions flow along their concentration gradient to maintain the resting potential of a neuron

Which term describes an electrical signal generated by neurons? a. resting potential b. equilibrium potential c. membrane potential d. action potential

d. action potential

A nerve impulse moves away from a neuron's cell body along ________. a. dendrites b. Nissl bodies c. synapses d. axon e. glia

d. axon Axons conduct a nerve impulse away from the cell body

Conduction of an Action Potential description

As the change in charge difference across the membrane spreads from open sodium channels, other sodium channels farther along the axon begin to open. The original sodium channels close and adjacent potassium channels open. As potassium ions move out of the cell, the original charge difference across the membrane is restored and then the potassium channels close. Meanwhile, new sodium channels open, followed by the opening of new potassium channels and the closing of sodium channels. In this manner, the action potential is propagated along the axon of the neuron, eventually reaching another cell. The information carried by this action potential will be processed with other information.

How neurons work

Each neuron receives input from one or more cells. In response, the neuron may generate an electrical signal known as an action potential that travels down the length of the axon.

Resting Potential description

Even without an action potential, the axon is a busy place, with many ions moving across its membrane. Much of this ion movement is driven by the sodium-potassium pump. Using energy from ATP, sodium potassium pumps actively transport sodium ions out of the cell and potassium ions in creating an uneven distribution of charge across the membrane. Some potassium channels are open all the time, allowing potassium ions to leave the cell. As a result of these ion movements, the inside of the cell is negative relative to the outside. This condition is called the resting potential

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

False Action potentials travel in only one direction down an axon because sodium channels in the neuron are refractory

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

False The potential energy of a membrane potential comes from the difference in electrical charge and from the concentration gradient of ions across a membrane

The synapse description

Signals are passed from a sending neuron to a receiving neuron at a junction called a synapse. An action potential in the sending neuron travels down the axon until it reaches a synaptic terminal. The narrow gap between the synaptic terminal and the receiving neuron is called the synaptic cleft.

Action Potential description

The membrane of an axon is also packed with gated ion channels that open and close during an action potential. At resting potential, the gated channels are closed. If a stimulus changes the distribution of charge across the membrane sufficiently, the gated sodium channels open. Movement of sodium ions across the membrane makes the inside of the cell more positive. This reversal of the charge distribution causes the gated sodium channels to close and the gated potassium channels to open. As potassium ions move out of the cell, the original charge difference is re-established across the membrane, closing the gated potassium channels. This sequence of events is called the action potential. The sodium-potassium pump restores the distribution of ions back to their levels at resting potential.

If the membrane potential of a neuron decreases, the membrane potential _____. a. remains unchanged b. becomes less negative c. becomes more negative

b. becomes less negative

Neurotransmitters descrition

The synaptic terminal of a sending neuron contains numerous vesicles filled with neurotransmitters, chemicals that carry information across the synaptic cleft. When an action potential reaches the synaptic terminals, the vesicles fuse with the plasma membrane of the sending neuron, releasing neurotransmitters into the synaptic cleft. The neurotransmitters affect the receiving neuron, changing the distribution of charge across its membrane. An action potential is propagated down an axon by the opening and closing of sodium and potassium channels. When an action potential arrives at the synaptic terminal, it causes the opening of calcium channels. Calcium ions enter the synaptic terminal through the calcium channels. Calcium ions bind to the vesicles containing neurotransmitters. This causes the vesicles to fuse with the plasma membrane of the sending neuron, releasing neurotransmitters into the synaptic cleft. The neurotransmitters diffuse across the synaptic cleft and bind to receptors in the plasma membrane of the receiving neuron. Neurotransmitters are quickly removed from the synaptic cleft, ending their effect on the receiving neuron

Why is an action potential an all-or-none response to stimuli? a. because voltage-gated ion channels open when membrane potential passes a particular level b. because a typical neuron receives signals through multiple dendrites but transmits signals through a single axon c. because neurons contain gated ion channels that are either open or closed

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

A nerve impulse moves toward a neuron's cell body along ________. a. dendrites b. synaptic terminals c. oligodendrocytes d. axons e. nodes of Ranvier

a. dendrites Dendrites conduct an impulse from a synapse toward the cell body

Of these choices, neuronal communication between the brain and the muscles of the leg is best conceptualized as ________. a. electrical and chemical signaling b. the transcription and translation of genes c. the transcription of genes d. chemical signaling e. electrical signaling

a. electrical and chemical signaling

The plasma membrane of a neuron has voltage-gated sodium and potassium channels. What is the effect of membrane depolarization on these channels? a. membrane depolarization first opens sodium channels and then opens potassium channels b. membrane depolarization first opens sodium channels at the same time c. membrane depolarization opens sodium channels but closes potassium channels

a. membrane depolarization first opens sodium channels and then opens potassium channels

Which term describe the difference in electrical charge across a membrane? a. membrane potential b. electrical potential c. electrical current d. resting potential

a. membrane potential

Temporal summation always involves ________. a. multiple inputs at a single synapse b. both inhibitory and excitatory inputs c. electrical synapses d. inputs that are not simultaneous e. synapses at more than one site

a. multiple inputs at a single synapse

Identify the correct statement(s) about the resting membrane potential of a cell. a. potassium and sodium gradients are maintained by active transport in a resting mammalian neuron b. neurons are the only cells that have a charge difference across their membranes c. concentration gradients of potassium and sodium across the plasma membrane represent potential energy

a. potassium and sodium gradients are maintained by active transport in a resting mammalian neuron c. concentration gradients of potassium and sodium across the plasma membrane represent potential energy

Which of the following terms describes how a neuronal membrane's potential is altered in the presence of inhibitory signals? a. Depolarization b. Hyperpolarization c. Polarization d. Repolarization

b. hyperpolarization Inhibitory signals hyperpolarize the membrane and make the membrane potential even more negative than normal.

What causes the falling phase of the action potential? a. the opening of voltage-gated sodium channels b. inactivation of voltage-gated sodium channels and the opening of voltage-gated potassium channels c. the opening of voltage-gated potassium channels

b. inactivation of voltage-gated sodium channels and the opening of voltage-gated potassium channels

The transmission first triggers the _________. a. action of the sodium-potassium pump b. opening of voltage-gated sodium channels and the diffusion of sodium ions into the neuron c. opening of voltage-gated sodium channels and the diffusion of sodium ions out of the neuron d. opening of voltage-gated potassium channels and the diffusion of potassium ions out of the neuron e. opening of voltage-gated potassium channels and the diffusion of potassium ions into the neuron

b. opening of voltage-gated sodium channels and the diffusion of sodium ions into the neuron This is the first of the events listed here. As a result of the inward flux of sodium ions, that region of the neuron depolarizes.

What happens when a resting neuron's membrane depolarizes? a. the neuron is less likely to generate an action potential b. the neuron's membrane voltage becomes more positive c. the cell's inside is more negative than the outside d. there is a net diffusion of Na+ out of the cell e. the equilibrium potential for K+ becomes more positive

b. the neuron's membrane voltage becomes more positive

Which structure is not part of a neuron? a. dendrite b. axons c. myelin sheath d. cell body

c. myelin sheath Myelin sheath is just a layer of Schwann cells wrapped around a neuron

Axons insulated by a(n) ______ are able to conduct ipulses faster than those not so insulated. a. node of Ranvier b. synaptic terminal c. myelin sheath d. layer of asbestos e astrocytes

c. myelin sheath Myelin sheaths, formed when Schwann cells wrap around an axon, allow such neurons to conduct impulses more rapidly than unmyelinated axons.

An impulse relayed along to myelinated axon "jumps" from ______ to _______. a. oligodendrocyte / Schwann cell b. node of Ranvier / Schwann cell c. node of Ranvier / node of Ranvier d. Scwann cell / Schwann cell e. Schwann cell / node of Ranvier

c. node of Ranvier / node of Ranvier In myelinated neurons the impulse jumps from node to node.

A stimulus has opened the voltage-gated sodium channel 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. a. potassium / opening of voltage-gated potassium channels b. sodium / opening of voltage-gated potassium channels c. sodium / opening of voltage-gated sodium channels d. sodium / closing of voltage-gated sodium channels e. potassium / opening of voltage-gated sodium channels

c. sodium / opening of voltage-gated sodium channels

What part of a neuron relays signals from one neuron to another neuron or to an effector? a. dendrite b. axon hillock c. synaptic terminal d. axon e. node of Ranvier

c. synaptic terminal Synaptic terminals contain neurotransmitter molecules that relay the nerve impulse across a synapse

Why are action potentials usually conducted in one direction? a. the axon hillock has a higher membrane potential than the terminals of the axon b. ions can flow along the axon in only one direction c. the brief refractory period prevents reopening of voltage-gated NA+ channels d. the nodes of Ranvier conduct potentials in one direction e. voltage-gated channels for both Na+ and K+ open in only one direction

c. the brief refractory period reopening of voltage-gated Na+ channels

How is an action potential propagated down an axon after voltage-gated sodium channels open in a region of the neuron's membrane? a. Potassium ions enter the neuron and diffuse to adjacent areas, resulting in the opening of voltage-gated sodium channels farther down the axon b. potassium ions enter the neuron and diffuse to adjacent areas, resulting in the opening of voltage-gated potassium channels farther down the axon c. sodium ions enter the neuron and diffuse to adjacent areas, resulting in the opening of voltage-gated potassium channels farther down the axon d. sodium ions enter the neuron and diffuse to adjacent areas, resulting in the opening of voltage-gated sodium channels farther down the axon

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

Which event triggers the creation of an action potential? a. the sodium-potassium pump shuttles ions across the membrane b. there is an undershoot of the resting potential c. Voltage-gated potassium channels open, and K+ ions diffuse out of the neuron d. the membrane depolarizes above the certain threshold potential

d. the membrane depolarizes above the certain threshold potential

What are neurotransmitter receptors located? a. synaptic vesicles membranes b. the nodes of Ranvier c. the nuclear membrane d. the postsynaptic membrane e. the myelin sheath

d. the postsynaptic membrane

What behavior is observed if the voltage across a neuronal membrane is set to -20mV? a. the potassium channel opens, and K+ ions flow in b. the sodium channel opens, and NA+ ions flow out c. the voltage-gated sodium and potassium channels both remain closed d. the sodium channel opens, and NA+ ions flow in

d. the sodium channel opens, and NA+ ions flow in

At rest, which of these plays a role in establishing the charge differential across a neuron's plasma membrane? a. the sodium-potassium pump moving sodium ions into the neuron and potassium ions out of the neuron b. the diffusion of sodium ions out of the neuron c. the diffusion of potassium ions into the neuron d. the sodium-potassium pump moving sodium ions out of the neuron and potassium ions into the neuron e. the diffusion of sodium ions into the neuron

d. the sodium-potassium pump moving the sodium ions out of the neuron and potassium ions into the neuron The net loss of positive ions establishes a charge differential across the plasma membrane.

Which of the following statements about action potential in a given neuron is false? a. they occur after the threshold potential is reached b. they are identical in magnitude c. they are identical in duration d. they are propagated down the length of the dendrite

d. they are propagated down the length of the denrite