Anatomy & Physiology Chapter 11 Homework

axon The axon is the conducting region of the neuron. It generates nerve impulses (action potentials) and transmits them, typically away from the cell body, along the axolemma (cell membrane of the axon).

Which part of the neuron is responsible for generating a nerve impulse? dendrite chromatophilic substance axon soma

B The astrocytes within the CNS support neurons and anchor them to their nutrient source.

Which of the neuroglial cell types shown is the most abundant in the CNS? A B C D E

D Despite the hyperpolarized state of the membrane at point D, a significantly strong stimulus may create enough depolarization to return the membrane to threshold. Point D would be considered within the relative refractory period. An important consequence of this design is that greater stimulus intensity will result in an increase in nerve impulse frequency.

At which of the points along the illustrated action potential can a second action potential be produced, but only with a stimulus significantly greater than that which produced the first? B C D E

B Voltage-gated Na+ channels open when the membrane potential reaches threshold and soon close when temporarily inactivated during the repolarization phase (C).

At which point of the illustrated action potential are the most gated Na+ channels open? A B C D E

anterograde axonal transport

Cold sores on the skin of the mouth occur when herpes simplex viruses that are dormant in neural ganglia become active and travel to the skin of the mouth. Which of the following is the mechanism by which these viruses travel from the ganglia (located within the head) to the skin of the mouth? transport along nerve impulses that travel down the axons anterograde axonal transport retrograde axonal transport travel of the viruses along neurofibrils

A The defects in nerve transmission associated with MS are caused by a loss of myelin within the CNS. Myelin within the CNS is primarily produced by the oligodendrocytes shown in A.

Destruction of which of the neuroglial cell types leads to the disease multiple sclerosis (MS)? A B C D F

oligodendrocytes Oligodendrocytes are a type of neuroglial cell that function to form the myelin sheath around the axons of neurons within the central nervous system.

In multiple sclerosis, the cells that are the target of an autoimmune attack are the _________. neurons muscle cells Schwann cells oligodendrocytes

C Graded potentials originating in the dendrites and cell body are integrated (summated) at the axon hillock (C). Membrane potentials above threshold at the hillock will open voltage gated Na+ channels found in the "trigger zone," producing an action potential that proceeds down the axon.

In which area of the neuron is an action potential initially generated? A B C D E

Touch stimulation of this sensory receptor will open the mechanically gated ion channels, but action potentials are still not initiated because propagation of an action potential requires the opening of voltage-gated Na+ channels. Propagation (spreading) of an action potential from the cell body to the axon hillock and eventually the axon terminals (synaptic knobs) requires the sequential opening of mechanically and voltage-gated ion channels. When the sequence is interrupted, the message cannot spread to the sensory regions of the central nervous system, causing numbness.

Local anesthetics block voltage-gated Na+ channels, but they do not block mechanically gated ion channels. Sensory receptors for touch (and pressure) respond to physical deformation of the receptors, resulting in the opening of specific mechanically gated ion channels. Why does injection of a local anesthetic into a finger still cause a loss of the sensation of touch from the finger? The local anesthetic prevents Na+ from causing the initial depolarization of this sensory receptor. The local anesthetic prevents any type of repolarization of this sensory receptor. Touch stimulation of this sensory receptor requires that there be a simultaneous opening of voltage-gated Na+ channels and mechanically gated ion channels. Touch stimulation of this sensory receptor will open the mechanically gated ion channels, but action potentials are still not initiated because propagation of an action potential requires the opening of voltage-gated Na+ channels.

True The billions of neurons, also called nerve cells, are the structural units of the nervous system. They are typically large, highly specialized cells that conduct messages in the form of nerve impulses from one part of the body to another.

Neurons are also called nerve cells. True False

True Opening K+ or Cl- channels in a postsynaptic membrane, resulting in K+ efflux or Cl- influx, respectively, would induce hyperpolarization. As the membrane potential increases and is driven farther from the axon's threshold, the postsynaptic neuron becomes less and less likely to "fire," and larger depolarizing currents are required to induce an action potential (AP). Hyperpolarizing changes in potential are called inhibitory postsynaptic potentials (IPSPs).

Opening K+ or Cl- channels in a postsynaptic membrane would produce an inhibitory postsynaptic potential (IPSP). True False

Ions diffusing out of the presynaptic cell can enter the postsynaptic cell, but cannot reenter the presynaptic cell. Ion movement between neurons is important in electrical synapses, but not in a chemical synapse, such as that shown in this figure.

Signals generated at a chemical synapse are said to move only in the direction of the presynaptic cell to the postsynaptic cell. Which of the following statements regarding the mechanisms determining this one way transmission is INCORRECT? The contents of synaptic vesicles are released from presynaptic membranes, not from postsynaptic membranes. Neurotransmitter receptors are found in the postsynaptic membranes, not in the presynaptic membranes. Ions diffusing out of the presynaptic cell can enter the postsynaptic cell, but cannot reenter the presynaptic cell. All of the listed responses are correct.

resting membrane potential At rest, the cell membrane is about 25 times more permeable to potassium than to sodium, and so more potassium ions diffuse out of the neuron down their concentration gradient than sodium ions diffuse into the neuron down theirs. The consequence is a cell membrane that has more positive charges (ions) along its external surface and relatively more negative charges along its internal surface. This separation of charges, or membrane voltage, is called the resting membrane potential.

The __________ is due to the difference in K+ and Na+ concentrations on either side of the plasma membrane, and the difference in permeability of the membrane to these ions. active potential intermittent membrane potential resting membrane potential dendrite potential

A Oligodendrocytes form myelin sheaths within the white matter of the CNS.

Which of the neuroglial cell types shown form myelin sheaths within the CNS? A B C F

reuptake of the neurotransmitter by transport into the postsynaptic cell Neurotransmitters are generally not transported into the postsynaptic cell upon which they exert their effects.

The box labeled D illustrates three mechanisms by which the effects of a neurotransmitter may be terminated. Which of the following mechanisms is NOT included in the figure? reuptake of the neurotransmitter by transport into the presynaptic cell breakdown of the neurotransmitter within the synaptic cleft diffusion of the neurotransmitter out of the synaptic cleft reuptake of the neurotransmitter by transport into the postsynaptic cell

reverberating circuits Reverberating circuits are involved in the control of rhythmic activities such as breathing, the sleep-wake cycle, and repetitive motor activities like walking. A signal travels through a chain of neurons, each feeding back to previous neurons in the pathway.

Which neuron circuit pattern is involved in the control of rhythmic activities such as breathing? parallel after-discharge circuit diverging circuit reverberating circuit converging circuit

False Actually, the sodium-potassium pump ejects three Na+ from the cell and then transports two K+ back into the cell. This action is essential to maintaining the concentration gradients for sodium and potassium, which are needed to generate and maintain the resting membrane potential.

The sodium-potassium pump ejects two Na+ from the cell and then transports three K+ back into the cell in order to maintain the concentration gradients for sodium and potassium. True False

False Myelinated fibers (axons bearing a myelin sheath) conduct nerve impulses rapidly, whereas unmyelinated fibers conduct impulses more slowly. Note that myelin sheaths are associated only with axons; dendrites are always nonmyelinated.

Unmyelinated fibers conduct impulses faster than myelinated fibers. True False

the voltage measured across the axon membrane at a specific point as an action potential travels past It is important to recognize that an identical event will begin in the adjacent area of the axon membrane as the action potential observed here decays.

What change in a neuron is being measured in the graph? the speed of an action potential as it moves down the length of an axon the voltage measured across the axon membrane at a specific point as an action potential travels past the voltage measured between the neuron cell body and the axonal terminals as an action potential is generated and decays the voltage measured across the axon membrane at various points along an axon at a specific instance of time during an action potential

integration center The integration center receives sensory information (input), determines the proper response, and then signals the appropriate effector(s) to produce the response.

What component of the reflex arc determines the response to a stimulus? integration center receptor effector sensory neuron

movement of Ca2+ into the interior of the axonal terminus through voltage-gated channels Depolarization caused by the action potential results in the opening of voltage-gated Ca2+ channels (indicated by A) in the membrane of the axonal terminus.

What event is depicted in the structure labeled A? movement of neurotransmitters into the interior of the axonal terminus through chemically gated channels movement of Ca2+ into the interior of the axonal terminus through voltage-gated channels movement of the action potential into the interior of the axonal terminus through voltage-gated channels movement of Na+ into the interior of the axonal terminus through chemically gated channels

diffusion of K+ out of the axon through gated ion channels The hyperpolarization phase (D) is characterized by the diffusion of K+ down its electrochemical gradient out of the axon. During this phase, voltage-gated Na+ channels are closed until another threshold event occurs.

What major ion currents occur at the point along the action potential phase labeled D? diffusion of Na+ out of the axon through gated ion channels diffusion of Na+ into the axon through gated ion channels diffusion of K+ into the axon through gated ion channels diffusion of both Na+ and K+ across the membrane in the direction of their respective electrochemical gradients diffusion of K+ out of the axon through gated ion channels

central nervous system The central nervous system, which consists of the brain and spinal cord, is the integrating and control center of the nervous system. It interprets sensory input and dictates motor output based on reflexes, current conditions, and past experience.

What part of the nervous system performs information processing and integration? somatic nervous system parasympathetic nervous system central nervous system sympathetic nervous system

unipolar The unipolar neuron has a single short process that emerges from the cell body and divides into proximal and distal branches. Such neurons are found chiefly in the ganglia in the PNS where they conduct sensory information.

What structural classification describes the neuron associated with the neuroglia shown by E and F? unipolar multipolar nonpolar bipolar

multipolar The neuron shown has a many processes (axons and dendrites) that emerge from the cell body. Such a neuron is described as multipolar and typically functions as a motor neuron or interneuron.

What structural classification describes this neuron? multipolar bipolar unipolar nonpolar

a threshold level depolarization The axolemma must be depolarized to threshold in order to generate an action potential.

What type of stimulus is required for an action potential to be generated? multiple stimuli a threshold level depolarization a suprathreshold stimulus hyperpolarization

E Neurotransmitters are stored in synaptic vesicles within axonal terminals for release into the synaptic cleft.

Which area would contain an abundance of vesicles containing neurotransmitter? A C D E

Both A and B The dendrites and soma of the cell receive signals from other neurons.

Which areas of this neuron would be classified as receptive regions? E only Both A and B D only Both A and E

the direction in which the nerve impluse travels relative to the central nervous system Functional classification groups neurons according to the direction in which the nerve impulse travels relative to the central nervous system. Based on this criterion, there are sensory neurons, motor neurons, and interneurons.

Which criterion is used to functionally classify neurons? whether the neurons are found within the CNS or the PNS the direction in which the nerve impulse travels relative to the central nervous system the number of processes extending from the cell body neuron whether the nerve fibers are myelinated or unmyelinated

B The cell body of neurons are alternatively termed perikaryon or soma.

Which lettered region in the figure is referred to as the soma? A B C D E

excitatory postsynaptic potential An excitatory postsynaptic potential, a type of graded potential, occurs because of the influx of Na+ through chemically gated channels in the receptive region, or postsynaptic membrane, of a neuron. Graded potentials are generated by chemically gated channels, whereas action potentials are produced by voltage-gated channels.

Which membrane potential occurs because of the influx of Na+ through chemically gated channels in the receptive region of a neuron? excitatory postsynaptic potential inhibitory postsynaptic potential inhibitory action potential action potential

astrocytes Astrocytes are the most abundant and versatile glial cells. Examples of their many functions include: anchoring neurons to capillaries, aiding in the exchanges between neurons and blood, guiding the migration of young neurons, and helping control the chemical environment around neurons.

Which neuroglia are the most abundant and versatile of the glial cells? Schwann cells ependymal cells astrocytes oligodendrocytes

endorphins Endorphins are natural opiates that inhibit substance P, the neurotransmitter that mediates pain transmission in the peripheral nervous system.

Which neurotransmitter(s) is/are the body's natural pain killer? acetylcholine endorphins norepinephrine substance P

the somatic nervous system The somatic nervous system is composed of somatic motor nerve fibers that conduct impulses from the central nervous system to skeletal muscles. It is often referred to as the voluntary nervous system because it allows us to consciously control our skeletal muscles.

Which of the following allows us to consciously control our skeletal muscles? the parasympathetic division of the autonomic nervous system the afferent division of the nervous system the somatic nervous system the sympathetic division of the autonomic nervous system

neurofibrils Microtubules and neurofibrils, which are bundles of intermediate filaments (neurofilaments), are important in maintaining cell shape and integrity. They form a network throughout the cell body.

Which of the following are bundles of neurofilaments that are important in maintaining the shape and integrity of neurons? axolemma perikaryon neurofibrils chromatophilic substance

nodes of Ranvier Adjacent Schwann cells along an axon do not touch one another, so there are gaps in the sheath. These myelin sheath gaps, or nodes of Ranvier, occur at regular intervals (about 1 mm apart) along a myelinated axon. Axon collaterals can emerge from the axon at these gaps.

Which of the following are gaps found along a myelin sheath? terminal boutons axolemma nodes of Ranvier outer collar of perinuclear cytoplasm

reverberating circuits Reverberating circuits are involved in the control of rhythmic activities such as breathing, the sleep-wake cycle, and repetitive motor activities such as walking. A signal travels through a chain of neurons, each feeding back to previous neurons in the pathway.

Which of the following circuit types is involved in the control of rhythmic activities such as the sleep-wake cycle, breathing, and certain motor activities (such as arm swinging when walking)? converging circuits diverging circuits reverberating circuits parallel after-discharge circuits

Spatial summation is used to increase the amplitude of a graded potential; temporal summation is used to increase the amplitude of an action potential.

Which of the following is NOT a difference between graded potentials and action potentials? Graded potentials can result from the opening of chemically gated channels; action potentials require the opening of voltage-gated channels. Spatial summation is used to increase the amplitude of a graded potential; temporal summation is used to increase the amplitude of an action potential. Greater stimulus intensity results in larger graded potentials, but not larger action potentials. Graded potentials occur along dendrites, whereas action potentials occur along axons.

multipolar Multipolar is a structural classification that groups neurons according to the number of processes extending from their cell body. Multipolar neurons have three or more processes - one axon and multiple dendrites.

Which of the following is NOT a functional classification of neurons? sensory interneurons efferent multipolar

pre-discharge circuits The patterns of synaptic connections in neuronal pools, called circuits, determine the pool's functional capabilities. Pre-discharge circuits are not one of the four basic types of circuits.

Which of the following is NOT a type of circuit? pre-discharge circuits diverging circuits converging circuits reverberating circuits

regulation of neurogenesis Most active during pre-natal development, neurogenesis (formation of neurons) is the process by which neurons are generated from neural stem cells. It is not one of the basic functions of the nervous system.

Which of the following is NOT one of the basic functions of the nervous system? integration of sensory input control the activity of muscles and glands regulation of neurogenesis monitor changes occurring both inside and outside the body

chlorides Neurotransmitters fall into several chemical classes based on molecular structure, but "chlorides" is not one of these classes.

Which of the following is NOT one of the chemical classes into which neurotransmitters fall? gases and lipids chlorides peptides amino acids

They are specialized for release and reception of chemical neurotransmitters. This is incorrect; electrical synapses do not involve the release and reception of neurotransmitters. Instead, the neurons are electrically coupled by gap junctions, which allow ions to flow directly from one neuron to the next.

Which of the following is NOT true of an electrical synapse? They are specialized for release and reception of chemical neurotransmitters. Transmission across these synapses is very rapid. Communication through these synapses may be unidirectional or bidirectional. They are less common than chemical synapses.

Most association neurons are confined witin the peripheral nervous system (PNS) Most association neurons are confined within the CNS (not PNS).

Which of the following is NOT true of association neurons? Association neurons account for over 99% of the neurons in the body. Association neurons are also known as interneurons. Most association neurons are multipolar. Most association neurons are confined within the peripheral nervous system (PNS).

degree of myelination of the axon The rate of impulse propagation depends largely on two factors, degree of myelination and axon diameter. The presence of a myelin sheath dramatically increases the rate of impulse (action potential) propagation. Heavily myelinated axons propagate impulses faster than lightly myelinated axons. Also, larger (thicker) axons conduct impulses faster than smaller (thinner) axons.

Which of the following is a factor that determines the rate of impulse propagation, or conduction velocity, along an axon? degree of myelination of the axon the number of axon collaterals extending from a truncated axon length of the axon whether the axon is located in the central nervous system or in the peripheral nervous system

opening of voltage gated Na+ channels The threshold value is the point at which voltage sensitive Na+ channels open. This leads to the characteristic rapid depolarization phase of the action potential.

Which of the following is expected to occur first if the membrane potential decrease shown in the graph were to reach the threshold value indicated at -55 mV? opening of voltage gated Na+ channels opening of chemically gated K+ channels opening of chemically gated Na+ channels opening of voltage-gated K+ channels the simultaneous opening of voltage-gated Na+ and K+ channels

axon Functionally, the axon is the conducting region of the neuron. It generates nerve impulses and transmits them, typically away from the cell body, along the plasma membrane, or axolemma.

Which of the following is the conducting region of the neuron? terminal boutons dendrites soma axon

A neuron can have only one axon, but the axon may have occasional branches along its length. This is true; a neuron can have only one axon, but the axon may have occasional branches along its length.

Which of the following is true of axons? Axons use chemically gated ion channels to generate graded potentials. A neuron can have only one axon, but the axon may have occasional branches along its length. Neurons can have multiple axons but only one dendrite. Smaller (thinner) axons are more likely to bear myelin sheaths than larger (thicker) axons.

An excitatory event may result in an action potential, but this will be less likely if the excitatory stimulus occurs during the response to the stimulus observed in the graph. Because the IPSP occurring in graph A results in a hyperpolarization of the neuron, a subsequent excitatory stimulus will be less likely to depolarize the membrane to threshold.

Which of the following is true regarding a response to an excitatory event which might occur soon after the initial stimulus indicated in the graph? An excitatory event will be more likely to generate an action potential if it occurs during the response to the stimulus observed in the graph. No action potential can be induced in the neuron by an excitatory event if it occurs during the response observed in the graph. An excitatory event may result in an action potential, but this will be less likely if the excitatory stimulus occurs during the response to the stimulus observed in the graph.

closure of the voltage-gated K+ channels

Which of the following mechanisms is most significant in returning the membrane potential to the resting state (from point D to point E)? closure of the voltage-gated K+ channels the opening of voltage gated Na+ channels the opening of voltage gated K+ channels the closing of leakage channels in the axon membrane

C and D Voltage-gated Na+ and K+ channels allow for the triggering of an action potential at the axon hillock (C) and its propagation down the axon (D).

Which of the following membrane regions would have significant numbers of voltage-gated Na+ and K+ ion channels? Voltage-gated ion channels are found in all areas of a typical neuron. C and D A only D only A and B

release of neurotransmitter into the synaptic cleft by exocytosis The influx of Ca2+ (shown by A) triggers the release of neurotransmitters stored in synaptic vesicles (B) by exocytosis.

Which of the following most accurately describes the involvement of the structure labeled B in synaptic signaling? release of Na+ and/or K+ ions into the synaptic cleft by facilitated diffusion release of neurotransmitter into the synaptic cleft by active transport release of neurotransmitter into the synaptic cleft by exocytosis release of Ca2+ into the synaptic cleft by exocytosis

Schwann cells Schwann cells (also called neurolemmocytes) surround all nerve fibers in the PNS and form myelin sheaths around the larger fibers. Myelin protects and electrically insulates nerve fibers, and it increases the transmission speed of nerve impulses.

Which of the following peripheral nervous system (PNS) neuroglia form the myelin sheaths around larger nerve fibers in the PNS? astrocytes Schwann cells oligodendrocytes satellite cells

Both responses are examples of graded potentials Both responses are short-lived, relatively small changes in the membrane potential.

Which of the following statements is true of both membrane potential responses shown in the graphs? Both responses are examples of graded potentials. Both responses are examples of EPSPs. Both responses are examples of action potentials. Both responses are examples of IPSPs.

the membrane potential of the postsynaptic membrane changes Binding of ligand (in this case a neurotransmitter) to a receptor (labeled C in the figure) causes the opening of receptor associated ion channels. Depending on the particular types of channels that open, diffusion of certain ions (typically Na+, K+, or Cl-) will cause a depolarizing or hyperpolarizing effect on the postsynaptic membrane.

Which of the following statements most accurately describes the effects caused by binding of the ligand shown to the structure labeled C? The ligand is transported into the presynaptic neuron. The membrane potential of the postsynaptic membrane changes. The membrane potential of the presynaptic membrane changes. The ligand is transported into the postsynaptic neuron.

microglia Microglial cells are small andovoid with relatively long "thorny" processes. Their processes touch nearby neurons, monitoring their health, and when they sense that certain neurons are injured or are in other trouble, the microglial cells migrate toward them. Where invading microorganisms or dead neurons are present, the microglial cells transform into a special type of macrophage that phagocytizes the microorganisms or neuronal debris.

Which of the following types of glial cells monitors the health of neurons, and can transform into a special type of macrophage to protect endangered neurons? ependymal cells oligodendrocytes astrocytes microglia

oligodendrocytes Oligodendrocytes wrap their processes around the thicker axons in the CNS, producing an insulating covering called a myelin sheath that increases the transmission speed of nerve impulses.

Which of the following types of glial cells produces the myelin sheaths that insulate axons, or nerve fibers, in the central nervous system (CNS)? microglia oligodendrocytes ependymal cells astrocytes

motor Motor, or efferent, neurons carry impulses away from the CNS to the effector organs (muscles and glands) of the body periphery.

Which of the following types of neurons carry impulses away from the central nervous system (CNS)? motor association afferent sensory

E The satellite cell shown by E wraps and insulates the soma of neurons within ganglia in the PNS.

Which of the neuroglial cell types shown are found in the PNS? A B C D E

D Ependymal cells line central cavities of the CNS. Much as the cilia of respiratory epithelium moves mucous along the surface of the tissue layer, the cilia of ependymal cells help circulate the cerebrospinal fluid that nourishes and cushions the brain and spinal cord.

Which of the neuroglial cell types shown control the flow of cerebrospinal fluid within the CNS? A B C D

serial processing In serial processing, the whole system works in a predictable, all-or-nothing manner. One neuron stimulates the next, which stimulates the next, and so on, eventually causing a specific, anticipated response. The most clear-cut examples of serial processing are spinal reflexes - rapid, automatic responses to stimuli in which a particular stimulus always causes the same response.

Which pattern of neural processing works in a predictable, all-or-nothing manner, where reflexes are rapid and automatic responses to stimuli in which a particular stimulus always causes the same response? oscillative processing parallel processing serial processing reflexive processing

opening of gated Na+ channels Opening of gated Na+ channels allows Na+ to diffuse into the neuron, causing an increase in the local membrane potential.

Which result of the stimulus applied is the likely cause of the response observed in the left graph? opening of gated Na+ channels opening of gated K+ channels opening of gated Cl- channels opening of gated Ca2+ channels