Mastering A&P Chapter 11: Fundamentals of the Nervous System and Nervous Tissue

Also called a nerve impulse transmitted by axons.

Action Potential

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

B. Leak channels [Leak channels for Na+ and K+ are ubiquitous, and they allow for the diffusion of these ions across plasma membranes.]

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

D. 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.]

What neuroglial cell type forms myelin sheaths within the CNS?

Oligodendrocytes [Oligodendrocytes form myelin sheaths within the white matter of the CNS.]

An exceptionally strong stimulus can trigger a response.

Relative Refractory Period

The neuron cannot respond to a second stimulus, no matter how strong.

Absolute Refractory Period

Assume you have a membrane with only potassium leak channels. The RMP is -90mV. Predict the RMP if we add Na+ leak channels. The most likely RMP value of Na+ is __________. A. -70 mV B. -90 mV C. +70 mV D. +90 mV E. -50 mV

A. -70 mV

Cl− is a common negatively charged extracellular ion. Predict the effect on the RMP if many Cl− gated channels are suddenly opened. A. A more negative RMP would result. B. There would be no change in the RMP. C. The membrane would become hypopolarized or have less charge separation across the membrane. D. The RMP would become more positive.

A. A more negative RMP would result. [Cl− is negatively charged and has a higher concentration in the ECF. The opening of Cl− channels would allow more negative charge to attempt to enter the cytoplasm. If the cell's normal RMP were -70mV, it would now become more negative. The farther away the RMP is from zero, either in the positive or negative direction, the greater the separation of charges is. This is called hyperpolarization. When the RMP moves closer to 0mV, it is known as depolarization.]

What prevents the Na+ and K+ gradients from dissipating? A. Na+-K+ ATPase B. Na+ and K+ leaks C. H+-K+ ATPase D. Na+ cotransporter

A. Na+-K+ ATPase [Also known as the Na+-K+ pump, or simply the pump, this transporter moves three Na+ out of the cell and two K+ into the cell for every ATP it hydrolyzes. This pumping action prevents the Na+ and K+ gradients from running down as these ions passively move through leak channels.]

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

A. Once the membrane depolarizes to a peak value of +30 mV, it repolarizes to its negative resting value of -70 mV. [The plasma membrane was depolarized to a positive value at the peak of the first phase of the action potential. Thus, it must repolarize back to a negative value.]

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? A. Resting membrane potential (RMP) B. Positive membrane potential C. Action potential D. Threshold potential

A. Resting membrane potential (RMP) [The resting membrane potential is the baseline potential that can be recorded across the plasma membrane of an excitable cell prior to excitation.]

On average, the resting membrane potential is -70 mV. What does the sign and magnitude of this value tell you? A. The inside surface of the plasma membrane is much more negatively charged than the outside surface. B. The outside surface of the plasma membrane is much more negatively charged than the inside surface. C. There is no electrical potential difference between the inside and the outside surfaces of the plasma membrane. D. The inside surface of the plasma membrane is much more positively charged than the inside surface.

A. The inside surface of the plasma membrane is much more negatively charged than the outside surface. [The inside surface of the plasma membrane accumulates more negative charge because of the presence of Na+ and K+ gradients and the selective permeability of the membrane to Na+ and K+.]

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. A. The presence of concentration gradients and leak channels B. The presence of concentration gradients and Na+-K+ pumps C. The presence of concentration gradients and voltage-gated channels D. The presence of a resting membrane potential and leak channels

A. The presence of concentration gradients and leak channels [The concentration gradient and the large number of K+ leak channels allow for rather robust K+ diffusion out of a cell. In contrast, the concentration gradient and the relatively few Na+ leak channels allow for much less Na+ diffusion into a cell.]

What is the first change to occur in response to a threshold stimulus? A. Voltage-gated Na+ channels change shape, and their activation gates open. B. Voltage-gated Na+ channels change shape, and their inactivation gates close. C. Voltage-gated Ca2+ channels change shape, and their activation gates open. D. Voltage-gated K+ channels change shape, and their activation gates open.

A. Voltage-gated Na+ channels change shape, and their activation gates open. [The activation gates of voltage-gated Na+ channels open very rapidly in response to threshold stimuli. The activation gates of voltage-gated K+ channels are comparatively slow to open.]

Which of the following is the conducting region of the neuron? A. axon B. dendrites C. terminal boutons D. soma

A. 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.]

What part of the nervous system performs information processing and integration? A. central nervous system B. sympathetic nervous system C. somatic nervous system D. parasympathetic nervous system

A. 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.]

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

A. chlorides

What does the central nervous system use to determine the strength of a stimulus? A. frequency of action potentials B. origin of the stimulus C. size of action potentials D. type of stimulus receptor

A. frequency of action potentials

What component of the reflex arc determines the response to a stimulus? A. integration center B. effector C. sensory neuron D. receptor

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

When neurotransmitter molecules bind to receptors in the plasma membrane of the receiving neuron, A. ion channels in the plasma membrane of the receiving neuron open. B. the receiving neuron becomes more positive inside. C. ion channels in the plasma membrane of the sending neuron open. D. the receiving neuron becomes more negative inside. E. vesicles in the synaptic terminal fuse to the plasma membrane of the sending neuron.

A. ion channels in the plasma membrane of the receiving neuron open.

The small space between the sending neuron and the receiving neuron is the A. synaptic cleft. B. synaptic terminal. C. calcium channel. D. neurotransmitter. E. vesicle.

A. synaptic cleft. [The synaptic cleft is the small space between the sending neuron and the receiving neuron.]

If a signal from a sending neuron makes the receiving neuron more negative inside, A. the receiving neuron is less likely to generate an action potential. B. the receiving neuron immediately generates an action potential. C. the sending neuron becomes more positive inside. D. the sending neuron becomes more negative inside. E. the receiving neuron is more likely to generate an action potential.

A. the receiving neuron is less likely to generate an action potential.

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

A. 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.]

What neuroglial cell type is the most abundant in the CNS?

Astrocytes [The astrocytes within the CNS support neurons and anchor them to their nutrient source.]

Which area of a neuron would contain an abundance of vesicles containing neurotransmitter?

Axon terminals [Neurotransmitters are stored in synaptic vesicles within axonal terminals for release into the synaptic cleft.]

You are going to record RMP from a cell using an electrode. You place your electrode and record a resting membrane potential every millisecond. You record an initial value of -70mV; however, over time you notice that your recordings become more and more positive until the RMP reaches 0mV. Assuming that and are the major determinants of RMP in this cell, which of the following could best explain your results? A. The cell is becoming depleted of K+. B. The cell's Na+−K+ ATPase pumps have stopped functioning. C. The cell's Na+ leak channels have stopped functioning. D. The cell's K+ leak channels have stopped functioning. E. The cell is becoming depleted of Na+.

B. The cell's Na+−K+ ATPase pumps have stopped functioning. [Since the RMP eventually becomes zero, the concentration of ions on either side of the membrane would be roughly equal. Without active processes to maintain concentration gradients, we would expect the concentration of ions on either side of the membrane to equilibrate.]

Which statement best characterizes a K+ leak channel? A. Chemically gated K+ channels that open and close according to the binding of other molecules. B. Trans-membrane protein channels that are always open to allow K+ to cross the membrane without the additional input of energy. C. Common trans-membrane channels are always open for any ion to move through in the presence of K+. D. Trans-membrane channels that use energy to allow the movement of K+ across the membrane.

B. Trans-membrane protein channels that are always open to allow K+ to cross the membrane without the additional input of energy.

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? A. transport along nerve impulses that travel down the axons B. anterograde axonal transport C. retrograde axonal transport D. travel of the viruses along neurofibrils

B. anterograde axonal transport

What is the role of acetylcholinesterase? A. stimulate the production of acetylcholine B. destroy ACh a brief period after its release by the axon endings C. act as a transmitting agent D. amplify or enhance the effect of ACh

B. destroy ACh a brief period after its release by the axon endings

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? A. ependymal cells B. microglia C. oligodendrocytes D. astrocytes

B. 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.]

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

B. neurotransmitter. [Neurotransmitter molecules carry information across a synaptic cleft.]

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

B. 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.]

Where do most action potentials originate? A. Axon terminal B. Cell body C. Initial segment D. Nodes of Ranvier

C. Initial segment [The first part of the axon is known as the initial segment. The initial segment is adjacent to the tapered end of the cell body, known as the axon hillock.]

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

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

Imagine that the cell membrane from the previous problem becomes more permeable to Na+. Predict how this will affect the RMP. A. The RMP will be more negative. B. The RMP will be zero. C. The RMP will be more positive. D. The RMP will be unaffected.

C. The RMP will be more positive.

Which part of the neuron is responsible for generating a nerve impulse? A. chromatophilic substance B. dendrite C. axon D. soma

C. 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 neurotransmitter(s) is/are the body's natural pain killer? A. acetylcholine B. substance P C. endorphins D. norepinephrine

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

Which of the following is NOT a functional classification of neurons? A. efferent B. interneurons C. multipolar D. sensory

C. 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.]

What characterizes depolarization, the first phase of the action potential? A. The membrane potential changes to a less negative (but not a positive) value. B. The membrane potential reaches a threshold value and returns to the resting state. C. The membrane potential changes to a much more negative value. D. The membrane potential changes from a negative value to a positive value.

D. The membrane potential changes from a negative value to a positive value. [The plasma membrane, which was polarized to a negative value at the RMP, depolarizes to a positive value.]

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

D. The membrane potential must depolarize from the resting voltage of -70 mV to a threshold value of -55 mV. [This is the minimum value required to open enough voltage-gated Na+ channels so that depolarization is irreversible.]

The plasma membrane is much more permeable to K+ than to Na+. Why? A. There are many more voltage-gated K+ channels than voltage-gated Na+ channels. B. Ligand-gated cation channels favor a greater influx of Na+ than K+. C. The Na+-K+ pumps transport more K+ into cells than Na+ out of cells. D. There are many more K+ leak channels than Na+ leak channels in the plasma membrane.

D. There are many more K+ leak channels than Na+ leak channels in the plasma membrane. [More leak channels translates into more leakiness. Thus the outward flux of K+ is greater than the inward flux of Na+.]

What opens first in response to a threshold stimulus? A. Voltage-gated K+ channels B. Ligand-gated cation channels C. Ligand-gated Cl- channels D. Voltage-gated Na+ channels

D. Voltage-gated Na+ channels [The activation gates of voltage-gated Na+ channels open, and Na+ diffuses into the cytoplasm.]

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

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

The operation of the Na+−K+ ATPase pump __________. A. moves 2 Na+ to the ECF and 3 K+ to the cytoplasm B. releases 3 K+ to the ECF C.. releases 1 Na+ to the ECF and 1 K+ to the cytoplasm D. moves 3 Na+ to the ECF and 2 K+ to the cytoplasm

D. moves 3 Na+ to the ECF and 2 K+ to the cytoplasm [The pumps move more Na+ than K+, which counteracts the effect of the membrane being more permeable to K+ (more K+ leak channels than Na+).]

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

D. 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 gaps found along a myelin sheath? A. outer collar of perinuclear cytoplasm B. axolemma C. terminal boutons D. nodes of Ranvier

D. 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.]

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

D. 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.]

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

D. the direction in which the nerve impulse 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 areas of a neuron would be classified as receptive regions?

Dendrites and Soma [The dendrites and soma of the cell receive signals from other neurons.]

The interior of the cell becomes less negative due to an influx of sodium ions.

Depolarization

When calcium ions enter the synaptic terminal, A. they cause an action potential in the sending neuron. B. neurotransmitter molecules are quickly removed from the synaptic cleft. C. the inside of the receiving neuron becomes more negative. D. the inside of the receiving neuron becomes more positive. E. they cause vesicles containing neurotransmitter molecules to fuse to the plasma membrane of the sending neuron.

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

What neuroglial cell type controls the flow of cerebrospinal fluid within the CNS?

Ependymal cells [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.]

Unmyelinated fibers conduct impulses faster than myelinated fibers.

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.]

Destruction of which neuroglial cell type leads to the disease multiple sclerosis (MS)?

Oligodendrocytes [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.]

The specific period during which potassium ions diffuse out of the neuron due to a change in membrane permeability.

Repolarization

Neurons are also called nerve cells.

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.]