Chapter 48: the nervous system

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. True False

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

Which term describes an electrical signal generated by neurons? Membrane potential. Resting potential. Action potential. Equilibrium potential.

An action potential is a rapid electrical signal generated by neurons.

A nerve impulse moves toward a neuron's cell body along _____. dendrites synaptic terminals oligodendrocytes axons nodes of Ranvier

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

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

Membrane depolarization opens both types of channels, but they respond independently and sequentially. Sodium channels open first, initiating the action potential. As the action potential proceeds, the sodium channels become inactivated and remain inactivated until after the membrane returns to the resting potential and the channels close. Potassium channels open more slowly than sodium channels but remain open and functional throughout the action potential. Read about the generation of action potentials.

Axons insulated by a(n) _____ are able to conduct impulses faster than those not so insulated. node of Ranvier synaptic terminal myelin sheath layer of asbestos astrocytes

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

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

multiple inputs at a single synapse.

An action potential moves along a(n) _____. myelin sheath axon dendrite synapse cell body

An axon is the only portion of a neuron capable of generating an action potential.

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

Resting neurons are most permeable to K+ ions.

The space between an axon of one neuron and the dendrite of another neuron is called a(n) _____. synaptic cleft node of Ranvier internodes synapse synaptic terminal

"Synaptic cleft" is the name given to the space between two neurons that meet at a synapse.

Which channel is mainly responsible for the resting potential of a neuron? Potassium leak channel. Voltage-gated sodium channel. Voltage-gated potassium channel. Chloride leak channel.

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

A nerve impulse moves away from a neuron's cell body along _____. dendrites Nissl bodies synapses axon glia

Axons conduct a nerve impulse away from the cell body.

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

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

The simultaneous arrival of graded depolarization and a graded hyperpolarization of equal but opposite magnitude at a particular location on the dendritic membrane is likely to _____. cause depolarization, because graded depolarizations are more important to neuron function cause hyperpolarization, because graded hyperpolarizations are more important to neuron function cancel each other out, making it appear as if there was no change in membrane potential cause the apoptosis of the neuron allow only the entry of sodium ions into the neuron, and prevent potassium ions from exiting the neuron

Grade potentials are summable, so a depolarization and a hyperpolarization can offset each other to make it appear that there were no changes in membrane potential at that location.

An impulse relayed along a myelinated axon "jumps" from _____ to _____. oligodendrocyte ... Schwann cell node of Ranvier ... Schwann cell node of Ranvier ... node of Ranvier Schwann cell ... Schwann cell Schwann cell ... node of Ranvier

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

Select the choice that describes neurons with the fastest conduction velocity for action potentials. thick, myelinated neurons thin, nonmyelinated neurons thick, nonmyelinated neurons thin, myelinated neurons All of these choices conduct action potentials at the same velocity.

Increased diameter and myelination yields very high conduction velocities for action potentials. [a]

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

Influx of Na+ ions into the neuron can lead to membrane depolarization above the threshold potential; this event triggers the creation of an action potential.

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

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

acetylcholine is an excitatory stimulus to the muscle binding of acetylcholine to its receptor triggers release of a second messenger, e.g., cAMP, inside the muscle these receptors have a corequisite binding of magnesium ions in order to function binding of acetylcholine to the receptor protein converts the protein to an open ion channel the receptors ionize as a result of binding acetylcholine, and this directly alters membrane potentials

Ionotropic receptors have both binding sites for their messenger ligands and the capacity to alter shape enough to become an open ion channel, allowing an increase in cross-membrane traffic of ions, thus altering the membrane potential.

Which term describes the difference in electrical charge across a membrane? Membrane potential. Resting potential. Electrical current. Electrical potential.

Membrane potential is the difference in electrical charge across a membrane.

What type of cell makes up the myelin sheath of a motor neuron? astrocytes microglial cells Ranvier cells ependymal cells Schwann cells

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

Choose the set that includes the most charged compounds that are more abundant inside neurons, in the cytosol, than outside the neurons, in the extracellular fluid. potassium ions and proteins sodium and potassium ions chloride ions and proteins proteins and sodium ions sodium and chloride ions

Proteins are abundant in all cells of the body and are mostly anions, thus contributing significantly to the membrane potential; and potassium ions are actively pumped into the cytosol of all cells in the body

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. The sodium channel opens, and Na+ ions flow out. The voltage-gated sodium and potassium channels both remain closed. The potassium channel opens, and K+ ions flow in.

Sodium ions flow into the cell when the membrane potential is between -20 mV and 30 mV.

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

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

Where in the neuron do action potentials begin? Dendrite. Cell body. Synapse. Axon hillock.

The axon hillock is the region where voltage-gated channels begin in a neuron, near the cell body.

A nerve poison that blocks acetylcholine receptors on dendrites would _____. reduce the binding of acetylcholine to its receptors on the postsynpatic membrane inhibit the regeneration of acetylcholine for use by the presynaptic terminals inactivate acetylcholinesterase, allowing acetylcholine to persist in the synapse cause continued stimulation of the postsynaptic membrane cause an immediate and enduring depolarization

The binding of neurotransmitter molecules to their specific receptors on the postsynaptic membrane opens ion channels, which completes the transmission of the impulse to the receiving cell. A nerve poison that blocked the acetylcholine receptors would prevent reception of the signal.

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

The brief refractory period prevents reopening of voltage-gated Na+ channels.

A neuron's nucleus is located in its _____. cell body axon myelin sheath dendrite synaptic terminals

The cell body is the region of a neuron where the nucleus is found.

The "information receiving" section of a neuron is its _____. Schwann cells dendrites glia axon terminal

The dendrites have receptor proteins that receive information by binding chemical messages called neurotransmitters. Together with the cell body, the dendrites receive signals from other neurons.

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

The entry of sodium ions into the neuron and their diffusion to adjacent areas of the membrane causes those portions of the membrane to become depolarized and results in the opening of voltage-gated sodium channels farther down the axon, which release potassium ions to the outside, returning the charge to its previous state.

Which structure is not part of a neuron? Cell body. Axons. Dendrite. Myelin sheath.

The myelin sheath is the layer of Schwann cells wrapped around a neuron.

What happens when a resting neuron's membrane depolarizes? There is a net diffusion of Na+ out of the cell. The neuron is less likely to generate an action potential. The cell's inside is more negative than the outside. The equilibrium potential for K+ (E K) becomes more positive. The neuron's membrane voltage becomes more positive.

The neuron's membrane voltage becomes more positive.

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

The sodium-potassium pump moves more sodium ions out of the cell than potassium ions into the cell; this net loss of positive ions establishes a charge differential across the plasma membrane.

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

The sodium-potassium pump moving Na+ ions out and K+ ions in - this channel maintains the ion concentration gradients across a neuronal membrane.

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

They are propagated down the length of 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. potassium ... opening of voltage-gated potassium channels sodium ... opening of voltage-gated potassium channels sodium ... opening of voltage-gated sodium channels sodium ... closing of voltage-gated sodium channels potassium ... opening of voltage-gated sodium channels

This describes part of the process by which an action potential travels along an axon.

The transmission first triggers the _____. action of the sodium-potassium pump opening of voltage-gated sodium channels and the diffusion of sodium ions into the neuron opening of voltage-gated sodium channels and the diffusion of sodium ions out of the neuron opening of voltage-gated potassium channels and the diffusion of potassium ions out of the neuron opening of voltage-gated potassium channels and the diffusion of potassium 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.

A neuron has a resting potential of about _____ millivolts. +50 +35 -55 -70 -80

This is the resting potential, the charge difference found across the plasma membrane of a "resting" neuron.

Neurons store neurotransmitter molecules in vesicles located within _____. the cell body myelin the synaptic cleft dendrites synaptic terminals

Vesicles within synaptic terminals contain neurotransmitter that may be released into the synaptic cleft.

Which of the following is a direct result of depolarizing the presynaptic membrane of an axon terminal? Synaptic vesicles fuse with the membrane. Voltage-gated calcium channels in the membrane open. The postsynaptic cell produces an action potential. Ligand-gated channels open, allowing neurotransmitters to enter the synaptic cleft. An EPSP or IPSP is generated in the postsynaptic cell.

Voltage-gated calcium channels in the membrane open.

Which of these causes the release of neurotransmitter molecules? the receipt of a signal from the postsynaptic neuron the opening of voltage-regulated calcium channels and the diffusion of calcium ions out of the neuron an action potential reaching the end of the cell body an action potential reaching the end of the axon an action potential reaching the end of the dendrite

When an action potential reaches the end of an axon, vesicles fuse with the plasma membrane and release neurotransmitter into the synaptic cleft. [d]

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

When the membrane potential of a neuron decreases, the negative value of the electrical potential across the plasma membrane is reduced and the membrane potential becomes more positive. Read about membrane potential.

A common feature of action potentials is that they move at the same speed along all axons. require the diffusion of Na+ and K+ through ligand-gated channels to propagate. cause the membrane to hyperpolarize and then depolarize. are triggered by a depolarization that reaches the threshold. can undergo temporal and spatial summation.

are triggered by a depolarization that reaches the threshold.

Where are neurotransmitter receptors located? the nodes of Ranvier the postsynaptic membrane the myelin sheath the nuclear membrane synaptic vesicle membranes

the postsynaptic membrane