Nerve Tissue & the Nervous System

Question 1

The ______, by far the most complex system in the body, is formed by a network of many billion ______ (______), all assisted by many more supporting cells called ______.

Answer 1

human nervous system, nerve cells, neurons, glial cells

Question 2

Each neuron has hundreds of interconnections with other ______, forming a very complex system for ______ and ______.

Answer 2

neurons, processing information, generating responses

Question 3

______ is distributed throughout the body as an integrated communications network.

Answer 3

Nerve tissue

Question 4

Anatomically, the general organization of the nervous system has two major divisions:

Answer 4

Central nervous system (CNS)
Peripheral nervous system (PNS)

Question 5

Anatomically, the general organization of the nervous system has two major divisions:

______, consisting of the brain and spinal cord

Answer 5

Central nervous system (CNS)

Question 6

Anatomically, the general organization of the nervous system has two major divisions:

______, composed of the cranial, spinal, and peripheral nerves conducting impulses to and from the CNS (sensory and motor nerves, respectively) and ______ that are small aggregates of nerve cells outside the CNS.

Answer 6

Peripheral nervous system (PNS), ganglia

Question 7

Anatomically the nervous system is divided into the ______ and ______, which have the major components.

Answer 7

CNS, PNS

Question 8

Functionally the nervous system consists of the following:

Answer 8

1. Sensory division (afferent)
   a. Somatic
   b. Visceral
2. Motor division (efferent)
   a. Somatic
   b. Autonomic

Question 9

Functionally the nervous system consists of the following:

Sensory division (______)
______ - sensory input perceived consciously (eg, from eyes, ears, skin, and musculoskeletal structures)

Answer 9

afferent, Somatic

Question 10

Functionally the nervous system consists of the following:

Sensory division (______)
______ - sensory input not perceived consciously (eg, from internal organs and cardiovascular structures)

Answer 10

afferent, Visceral

Question 11

Functionally the nervous system consists of the following:

Motor division (______)
______ - motor output controlled consciously or voluntarily (eg, by skeletal muscle effectors)

Answer 11

efferent, Somatic

Question 12

Functionally the nervous system consists of the following:

Motor division (______)
______ - motor output not controlled consciously (eg, by heart or gland effectors)

Answer 12

efferent, Autonomic

Question 13

The autonomic motor nerves, comprising what is often called the ______, all have pathways involving two neurons: a ______ neuron with the cell body in the CNS and a ______ neuron with the cell body in a ganglion.

Answer 13

autonomic nervous system (ANS), preganglionic, postganglionic

Question 14

The ANS has two divisions:

Answer 14

parasympathetic division
sympathetic division

Question 15

The ANS has two divisions:

The ______, with its ganglia within or near the effector organs, maintains normal body homeostasis.

Answer 15

parasympathetic division

Question 16

The ANS has two divisions:

The ______ has its ganglia close to the CNS and controls the body’s responses during emergencies and excitement.

Answer 16

sympathetic division

Question 17

ANS components located in the wall of the digestive tract are sometimes referred to as ______.

Answer 17

enteric nervous system

Question 18

Cells in both central and peripheral nerve tissue are of two kinds: ______, which typically have numerous long processes, and various ______ (Gr. glia, glue), which have short processes, support and protect neurons, and participate in many neural activities, neural nutrition, and defense of cells in the CNS.

Answer 18

neurons, glial cells

Question 19

Neurons respond to ______ (______) by altering the ______ that exists across their ______.

Answer 19

environmental changes, stimuli, ionic gradient, plasma membranes

Question 20

All cells maintain such a gradient (ionic gradient), also called an ______, but cells that can rapidly change this potential in response to stimuli (eg, neurons, muscle cells, some gland cells) are said to be ______ or ______.

Answer 20

electrical potential, excitable, irritable

Question 21

Neurons react promptly to stimuli with a reversal of the ______ (______) that generally spreads from the place that received the stimulus and is propagated across the neuron’s entire ______.

Answer 21

ionic gradient, membrane depolarization, plasma membrane

Question 22

This propagation, called the ______, the ______, or the ______, is capable of traveling long distances along neuronal processes, transmitting such signals to other neurons, muscles, and glands.

Answer 22

action potential, depolarization wave, nerve impulse

Question 23

Development of Nerve Tissue

1. The nervous system develops from the ______ of the three early embryonic layers, the ______, beginning in the ______ week of development

Answer 23

outermost, ectoderm, third

Question 24

Development of Nerve Tissue

2. With signals from the underlying axial structure, the ______, ectoderm on the mid-dorsal side of the embryo thickens to form the ______.

Answer 24

notochord, epithelial neural plate

Question 25

Development of Nerve Tissue

3. The sides of this plate fold upward and grow toward each other medially, and within a few days fuse to form the ______. Cells of this tube give rise to the entire ______, including ______ and most ______.

Answer 25

neural tube, CNS, neurons, glial cells

Question 26

Development of Nerve Tissue

4. As the folds fuse and the neural tube separates from the now overlying surface ______ that will form ______, a large population of developmentally important cells, the ______, separates from the neuroepithelium and becomes ______.

Answer 26

ectoderm, epidermis, neural crest, mesenchymal

Question 27

Development of Nerve Tissue

5. ______ migrate extensively and differentiate as all the cells of the ______, as well as a number of other ______.

Answer 27

Neural crest cells, PNS, non-neuronal cell types

Question 28

The functional unit in both the CNS and PNS is the ______. Some neuronal components have special names, such as “______” for the cell membrane.

Answer 28

neuron, neu-rolemma

Question 29

Most neurons have three main parts:

Answer 29

cell body
dendrites
axon

Question 30

Most neurons have three main parts:

The ______ (also called the ______ or ______), which contains the nucleus and most of the cell’s organelles and serves as the synthetic or trophic center for the entire neuron.

Answer 30

cell body, perikaryon, soma

Question 31

Most neurons have three main parts:

The ______, which are the numerous elongated processes extending from the perikaryon and specialized to receive stimuli from other neurons at unique sites called ______.

Answer 31

dendrites, synapses

Question 32

Most neurons have three main parts:

The ______, which is a single long process ending at synapses specialized to generate and conduct nerve impulses to other cells (eg, nerve, muscle, and gland cells).

Answer 32

axon

Question 33

Axons may also receive information from other neurons, information that mainly modifies the transmission of ______ to those neurons.

Answer 33

action potentials

Question 34

______ and their processes or “______” are variable in size and shape. Cell bodies can be very large, measuring up to ______ in diameter. Other neurons, such as those in the ______, are among the body’s ______ cells.

Answer 34

Neurons, nerve fibers, 150 μm, cerebellar granular layer, smallest

Question 35

Neurons can be classified according to the number of processes extending from the cell body:

Answer 35

Multipolar neurons
Bipolar neurons
Unipolar or pseudounipolar neurons
Anaxonic neurons

Question 36

Neurons can be classified according to the number of processes extending from the cell body:

______, each with one axon and two or more dendrites, are the most common.

Answer 36

Multipolar neurons

Question 37

Neurons can be classified according to the number of processes extending from the cell body:

______, with one dendrite and one axon, comprise the sensory neurons of the retina, the olfactory epithelium, and the inner ear.

Answer 37

Bipolar neurons

Question 38

Neurons can be classified according to the number of processes extending from the cell body:

______, which include all other sensory neurons, each have a single process that bifurcates close to the perikaryon, with the longer branch extending to a peripheral ending and the other toward the CNS.

Answer 38

Unipolar or pseudounipolar neurons

Question 39

Neurons can be classified according to the number of processes extending from the cell body:

______, with many dendrites but no true axon, do not produce action potentials, but regulate electrical changes of adjacent CNS neurons.

Answer 39

Anaxonic neurons

Question 40

Because the ______ emerging from cell bodies are seldom seen in sections of nervous tissue, it is difficult to classify neurons structurally by ______.

Answer 40

fine processes, microscopic inspection

Question 41

______ can also be subdivided functionally.

Answer 41

Nervous components

Question 42

______ neurons are afferent, receiving stimuli from receptors throughout the body.

Answer 42

Sensory

Question 43

______ neurons are efferent, sending impulses to effector organs such as muscle fibers and glands.

Answer 43

Motor

Question 44

______ motor nerves are under voluntary control and typically innervate skeletal muscle.

Answer 44

Somatic

Question 45

______ motor nerves control the involuntary or unconscious activities of glands, cardiac muscle, and most smooth muscle.

Answer 45

Autonomic

Question 46

______ establish relationships among other neurons, forming complex functional networks or circuits in the ______.

Answer 46

Interneurons, CNS

Question 47

Interneurons are either ______ or ______ and comprise ______% of all neurons in adults.

Answer 47

multipolar, anaxonic, 99

Question 48

In the CNS most neuronal perikarya occur in the ______, with their axons concentrated in the ______. These terms refer to the general appearance of unstained ______ caused in part by the different ______ of nerve cell bodies.

Answer 48

gray matter, white matter, CNS tissue, densities

Question 49

In the PNS cell bodies are found in ______ and in some ______, such as the ______, and axons are bundled in ______.

Answer 49

ganglia, sensory regions, olfactory mucosa, nerves

Question 50

______ is a slowly progressing disorder affecting muscular activity characterized by tremors, reduced activity of the facial muscles, loss of balance, and postural stiffness.

Answer 50

Parkinson disease

Question 51

Parkinson disease
It is caused by gradual loss by ______ of ______ neurons whose cell bodies lie within the nuclei of the ______.

Answer 51

apoptosis, dopamine- producing, CNS substantia nigra

Question 52

Parkinson disease is treated with ______ (______), a precursor of dopamine that augments the declining production of this neurotransmitter.

Answer 52

l-dopa, l-3,4-dihydroxyphenylalanine

Question 53

The neuronal ______ contains the nucleus and surrounding cytoplasm, exclusive of the cell processes.

Answer 53

cell body

Question 54

______
- It acts as a trophic center, producing most cytoplasm for the processes.

Answer 54

Cell Body

Question 55

Most cell bodies are in contact with a great number of ______ conveying ______ or ______ stimuli generated in other neurons.

Answer 55

nerve endings, excitatory, inhibitory

Question 56

A typical neuron has an unusually large, ______ nucleus with a prominent ______, indicating intense synthetic activity.

Answer 56

euchromatic, nucleolus

Question 57

Cytoplasm of perikarya often contains numerous ______ and highly developed ______, indicating active production of both ______ proteins and proteins for ______ and ______.

Answer 57

free polyribosomes, RER, cytoskeletal, transport, secretion

Question 58

Histologically these regions with concentrated RER and other polysomes are ______ and are distinguished as ______ (or ______, ______).

The amount of this material varies with the type and functional state of the neuron and is particularly abundant in large nerve cells such as ______ neurons.

Answer 58

basophilic, chromatophilic substance, Nissl substance, Nissl bodies, motor

Question 59

The ______ is located only in the cell body, but ______ can be found throughout the cell and are usually abundant in the ______.

Answer 59

Golgi apparatus, mitochondria, axon terminals

Question 60

In both perikarya and processes microtubules, ______ and ______ are abundant, with the latter formed by unique protein subunits and called ______ in this cell type.

Answer 60

actin filaments, intermediate filaments, neurofilaments

Question 61

Cross-linked with certain fixatives and impregnated with ______, neurofilaments are also referred to as ______ by light microscopists.

Answer 61

silver stains, neurofibrils

Question 62

Some nerve cell bodies also contain inclusions of pigmented material, such as ______, consisting of residual bodies left from ______.

Answer 62

lipofuscin, lysosomal digestion

Question 63

______ are typically short, small processes emerging and branching off the soma.

Answer 63

Dendrites

Question 64

Usually covered with many ______, dendrites are the principal ______ and ______ on neurons.

Answer 64

synapses, signal reception, processing sites

Question 65

The large number and extensive ______ of dendrites allow a single neuron to ______ and ______ signals from many other nerve cells.

Answer 65

arborization, receive, integrate

Question 66

For example, up to ______ axonal endings can make functional contact with the dendrites of a single large ______ of the ______.

Answer 66

200,000, Purkinje cell, cerebellum

Question 67

Unlike axons, which maintain a nearly constant diameter, dendrites become much ______ as they branch, with ______ elements predominating in these ______ regions.

Answer 67

thinner, cytoskeletal, distal

Question 68

In the CNS most synapses on dendrites occur on ______, which are dynamic membrane protrusions along the small ______, visualized with ______ and studied by ______ or ______ microscopy.

Answer 68

dendritic spines, dendritic branches, silver staining, confocal, electron

Question 69

______ serve as the initial processing sites for synaptic signals and occur in vast numbers, estimated to be on the order of ______ for cells of the ______.

Answer 69

Dendritic spines, 1014, human cerebral cortex

Question 70

Dendritic spine morphology depends on ______ and changes continuously as synaptic connections on neurons are modified.

Answer 70

actin filaments

Question 71

Changes in dendritic spines are of key importance in the constant changes of the ______ that occurs during embryonic brain development and underlies adaptation, learning, and memory postnatally.

Answer 71

neural plasticity

Question 72

Most neurons have only one ______, typically longer than its ______.

Answer 72

axon, dendrites

Question 73

Axonal processes vary in length and diameter according to the type of ______.

Answer 73

neuron

Question 74

Axons of the ______ neurons that innervate the foot muscles have lengths of nearly a ______; large cell bodies are required to maintain these axons, which contain most of such neurons’ ______.

Answer 74

motormeter, cytoplasm

Question 75

The plasma membrane of the axon is often called the ______ and its contents are known as ______.

Answer 75

axolemma, axoplasm

Question 76

Axons originate from a pyramid-shaped region of the perikaryon called the ______, just beyond which the ______ has concentrated ion channels that generate the ______. At this initial segment of the axon, the various ______ and ______ stimuli impinging on the neuron are algebraically summed, resulting in the decision to propagate—or not to propagate—a ______.

Answer 76

axon hillock, axolemma, action potential, excitatory, inhibitory, nerve impulse

Question 77

Axons generally branch ______ profusely than dendrites, but do undergo ______.

Answer 77

less, terminal arborization

Question 78

Axons of interneurons and some motor neurons also have major branches called ______ that end at smaller branches with synapses influencing the activity of many other neurons.

Answer 78

collaterals

Question 79

Each small axonal branch ends with a dilation called a ______ that contacts another neuron or non-nerve cell at a synapse to initiate an impulse in that cell.

Answer 79

terminal bouton

Question 80

______ contains mitochondria, microtubules, neuro- filaments, and transport vesicles, but very few ______ or ______, features that emphasize the dependence of axoplasm on the ______. If an axon is severed from its cell body, its distal part quickly degenerates and undergoes ______.

Answer 80

Axoplasm, polyribosomes, cisternae of RER, perikaryon, phagocytosis

Question 81

Lively ______ of molecules large and small occurs within axons

Answer 81

bidirectional transport

Question 82

Organelles and macromolecules synthesized in the cell body move by ______ along axonal microtubules via ______ from the perikaryon to the synaptic terminals.

Answer 82

anterograde transport, kinesin

Question 83

______ in the opposite direction along microtubules via ______ carries certain other macromolecules, such as material taken up by endocytosis (including viruses and toxins), from the periphery to the cell body.

Answer 83

Retrograde transport, dynein

Question 84

______ can be used to study the pathways of neurons: if peroxidase or another marker is injected into regions with ______, its later distribution throughout the neurons serving such regions can be determined histochemically.

Answer 84

Retrograde transport, axon terminals

Question 85

Anterograde and retrograde transports both occur fairly rapidly, at rates of ______.

Answer 85

50-400 mm/d

Question 86

A much slower ______, moving only a few millimeters per day, involves movement of the ______ itself. This slow axonal transport corresponds roughly to the rate of ______.

Answer 86

anterograde stream, axonal cytoskeleton, axon growth

Question 87

A ______, or an ______, travels along an axon like a spark moves along an explosive’s fuse.

Answer 87

nerve impulse, action potential

Question 88

______
- It is an electrochemical process initiated at the axon hillock when other impulses received at the cell body or dendrites meet a certain threshold.

Answer 88

Nerve Impulse

Question 89

The action potential is propagated along the axon as a wave of membrane depolarization produced by ______ channels in the ______ that allow diffusion of these ions into and out of the axoplasm.

Answer 89

voltage-gated Na+ and K+, axolemma

Question 90

The ______ around all regions of the neuron is a very thin zone immediately outside the cell that is formed by enclosing glial cells that also regulate its ionic contents.

Answer 90

extracellular compartment

Question 91

In unstimulated neurons, ______ Na-K pumps and other membrane proteins maintain an axoplasmic ______ only one-tenth of that outside the cell and a ______ many times greater than the extracellular concentration.

This produces a potential electrical difference across the axolemma of about ______, with the inside ______ to the outside.

This difference is the axon’s ______.

Answer 91

ATP-dependent, Na+ concentration, K+ level

–65 mV, negative

resting potential

Question 92

When the threshold for triggering an impulse is met, channels at the axon’s initial segment ______ and allow a very rapid influx of extracellular ______ that makes the axoplasm ______ in relation to the extracellular environment and shifts (______) the resting potential from ______ to ______, to ______ mV.

Answer 92

open, Na+, positive, depolarizes, negative, positive, +30

Question 93

Immediately after the membrane depolarization, the voltage-gated Na+ channels ______ and those for K+ ______, which rapidly returns the membrane to its ______.

Answer 93

close, open, resting potential

Question 94

Nerve Impulse
This cycle of events occurs in less than ______.

Answer 94

1 millisecond

Question 95

______ stimulates adjacent portions of the axolemma to depolarize and return immediately to the resting potential, which causes a nerve impulse, or wave of depolarization, to move rapidly along the axon.

Answer 95

Depolarization

Question 96

After a ______ also measured in milliseconds, the neuron is ready to repeat this process and generate another ______.

Answer 96

refractory period, action potential

Question 97

Impulses arriving at the synaptic nerve endings promote the discharge of stored ______ that ______ or ______ action potentials in another neuron or a non-neural cell.

Answer 97

neurotransmitter, stimulates, inhibits

Question 98

______ are sites where nerve impulses are transmitted from one neuron to another, or from neurons and other effector cells.

Answer 98

Synapses

Question 99

The structure of a synapse ensures that transmission is ______.

Answer 99

unidirectional

Question 100

Synapses convert an ______ signal (nerve impulse) from the ______ into a ______ signal that affects the ______.

Answer 100

electrical, presynaptic cell, chemical, postsynaptic cell

Question 101

Most synapses act by releasing ______, which are usually small molecules that bind specific receptor proteins to either open or close ion channels or initiate second- messenger cascades.

Answer 101

neurotransmitters

Question 102

A synapse has the following components:

Answer 102

presynaptic axon terminal (terminal bouton)
postsynaptic cell membrane
synaptic cleft

Question 103

A synapse has the following components:

The ______ (______) contains mitochondria and numerous synaptic vesicles from which neurotransmitter is released by exocytosis.

Answer 103

presynaptic axon terminal, terminal bouton

Question 104

A synapse has the following components:

The ______ contains receptors for the neurotransmitter, and ion channels or other mechanisms to initiate a new impulse.

Answer 104

postsynaptic cell membrane

Question 105

A synapse has the following components:

A 20- to 30-nm-wide intercellular space called the ______ separates these presynaptic and postsynaptic membranes.

Answer 105

synaptic cleft

Question 106

At the presynaptic region the nerve impulse briefly opens ______, promoting a ______ influx that triggers ______ release by exocytosis or similar mechanisms.

Answer 106

calcium channels, Ca2+, neurotransmitter

Question 107

Immediately the released neurotransmitter molecules diffuse across the ______ and bind ______ at the ______ region.

Answer 107

synaptic cleft, receptors, postsynaptic

Question 108

Immediately the released neurotransmitter molecules diffuse across the synaptic cleft and bind receptors at the postsynaptic region.

This produces either an excitatory or an inhibitory effect at the postsynaptic membrane, as follows:

• Neurotransmitters from ______ cause postsynaptic Na+ channels to open, and the resulting Na+ influx initiates a depolarization wave in the postsynaptic neuron or effector cell as just described.

Answer 108

excitatory synapses

Question 109

Immediately the released neurotransmitter molecules diffuse across the synaptic cleft and bind receptors at the postsynaptic region.

This produces either an excitatory or an inhibitory effect at the postsynaptic membrane, as follows:

• At ______ neurotransmitters open Cl– or other anion channels, causing influx of anions and hyperpolarization of the postsynaptic cell, making its membrane potential more negative and more resistant to depolarization.

Answer 109

inhibitory synapses

Question 110

Interplay between ______ and ______ effects on post- synaptic cells allows synapses to process neuronal input and fine-tune the reaction of the effector cell. Impulses passing from presynaptic neurons to postsynaptic cells are usually modified at the ______ by similar connections there with other neurons.

Answer 110

excitatory, inhibitory, synapse

Question 111

The response in ______ neurons is determined by the summation of activity at hundreds of synapses on that cell.

Answer 111

postsynaptic

Question 112

The chemical transmitter used at neuromuscular junctions and some synapses of the CNS is ______.

Answer 112

acetylcholine

Question 113

Within the CNS other major categories of neurotransmitters include the following:

Answer 113

amino acids
Monoamines
catecholamines
polypeptides

Question 114

Within the CNS other major categories of neurotransmitters include the following:

Certain ______ (often modified), such as gluta- mate and γ-aminobutyrate (GABA)

Answer 114

amino acids

Question 115

Within the CNS other major categories of neurotransmitters include the following:

______, such as serotonin (5-hydroxytryptamine or 5-HT)

Answer 115

Monoamines

Question 116

Within the CNS other major categories of neurotransmitters include the following:

______, such as dopamine, all of which are synthesized from amino acids

Answer 116

catecholamines

Question 117

Within the CNS other major categories of neurotransmitters include the following:

Small ______,such as endorphins and substance P.

Answer 117

polypeptides

Question 118

______ support neuronal survival and activities, and are ______ times more abundant than neurons in the mammalian brain.

Answer 118

Glial cells, 10

Question 119

Like neurons most glial cells develop from ______ of the ______. In the CNS glial cells surround both the ______ cell bodies, which are often larger than the glial cells, and the processes of axons and dendrites occupying the spaces between neurons.

Answer 119

progenitor cells, embryonic neural plate, neuronal

Question 120

Except around the larger blood vessels, the CNS has only a very small amount of ______ and ______.

Answer 120

connective tissue, collagen

Question 121

______ substitute for cells of connective tissue in some respects, supporting neurons and creating immediately around those cells microenvironments that are optimal for neuronal activity.

Answer 121

Glial cells

Question 122

The fibrous ______ of CNS tissue superficially resembles collagen by light microscopy, but is actually the network of fine cellular processes emerging from ______ and ______.

Such processes are collectively called the ______.

Answer 122

intercellular network, neurons, glial cells, neuropil

Question 123

______ extend many processes, each of which becomes sheetlike and wraps repeatedly around a portion of a nearby CNS axon.

During this wrapping most cytoplasm gradually moves out of the growing extension, leaving multiple compacted layers of cell membrane collectively termed ______.

Answer 123

Oligodendrocytes, myelin

Question 124

An axon’s full length is covered by the action of many ______.

Answer 124

oligodendrocytes

Question 125

Oligodendrocytes

The resulting ______ electrically insulates the axon and facilitates rapid transmission of nerve impulses.

Answer 125

myelin sheath

Question 126

Found only in the CNS oligodendrocytes are the predominant ______ in ______, which is white because of the lipid concentrated in the wrapped membrane sheaths.

Answer 126

glial cells, white matter

Question 127

The ______ and ______ are not visible by routine light microscope staining, in which oligodendrocytes usually appear as small cells with rounded, condensed ______ and unstained ______.

Answer 127

processes, sheaths, nuclei, cytoplasm

Question 128

Also unique to the CNS ______ have a large number of long radiating, branching processes.

Answer 128

astrocytes

Question 129

Proximal regions of the astrocytic processes are reinforced with bundles of intermediate filaments made of ______ (______), which serves as a unique marker for this glial cell.

Answer 129

glial fibrillary acid protein, GFAP

Question 130

Astrocytes

Distally the processes lack ______, are not readily seen by microscopy, and form a vast net- work of delicate terminals contacting synapses and other structures.

Answer 130

GFAP

Question 131

Astrocytes

Distally the processes lack ______, are not readily seen by microscopy, and form a vast net- work of delicate terminals contacting synapses and other structures.

Answer 131

GFAP

Question 132

______ processes of a single astrocyte typically occupy a large volume and associate with over a million synaptic sites.

Answer 132

Terminal

Question 133

Astrocytes originate from ______ in the embryonic neural tube and are by far the most ______ glial cells of the brain, as well as the most ______ structurally and functionally.

Answer 133

progenitor cells, numerous, diverse

Question 134

______ astrocytes, with long delicate processes, are abundant in ______; those with many shorter processes are called ______ astrocytes and predominate in the ______.

The highly variable and dynamic processes mediate most of these cells’ many functions.

Answer 134

Fibrous, white matter, protoplasmic, gray matter

Question 135

Functions attributed to astrocytes of various CNS regions include the following:

• ______ that associate with or cover synapses, affecting the formation, function, and plasticity of these structures
• ______ around neurons, with particular importance in buffering extracellular K+ levels
• ______ of differentiating neurons during CNS development

Answer 135

Extending processes
Regulating the extracellular ionic concentrations
Guiding and physically supporting movements and locations

Question 136

Astrocytes

Extending fibrous processes with expanded ______ that cover ______ cells and modulate ______ and help move nutrients, wastes, and other metabolites between neurons and capillaries.

Answer 136

perivascular feet, capillary endothelial, blood flow

Question 137

Astrocytes

Forming a barrier layer of expanded protoplasmic processes, called the ______, which lines the meninges at the external CNS surface.

Answer 137

glial limiting membrane

Question 138

Astrocytes

Filling tissue defects after CNS injury by proliferation to form an ______.

Answer 138

astrocytic scar

Question 139

Finally, astrocytes communicate directly with one another via ______, forming a very large cellular network for the coordinated regulation of their various activities in different brain regions.

Answer 139

gap junctions

Question 140

______ are columnar or cuboidal cells that line the fluid-filled ventricles of the brain and the central canal of the spinal cord.

Answer 140

Ependymal cells

Question 141

In some CNS locations, the apical ends of ependymal cells have ______, which facilitate the movement of ______ (______), and ______, which are likely involved in absorption.

Answer 141

cilia, cerebrospinal fluid, CSF, long microvilli

Question 142

Ependymal cells are joined apically by ______ complexes similar to those of epithelial cells. However, unlike a true epithelium there is no ______.

Answer 142

apical junctional, basal lamina

Question 143

Instead, the basal ends of ependymal cells are ______ and extend branching processes into the adjacent ______.

Answer 143

elongated, neuropil

Question 144

Less numerous than oligodendrocytes or astrocytes but nearly as common as neurons in some CNS regions, ______ are small cells with actively mobile processes evenly distributed throughout ______ and ______.

Answer 144

microglia, gray, white matter

Question 145

Unlike other glial cells ______ migrate, with their processes scanning the neuropil and removing damaged or effete synapses or other fibrous components.

Answer 145

microglia

Question 146

______ also constitute the major mechanism of immune defense in the CNS, removing any microbial invaders and secreting a number of immunoregulatory ______.

Answer 146

Microglial cells, cytokines

Question 147

Microglia do not originate from neural progenitor cells like other glia, but from circulating ______, belonging to the same family as macrophages and other antigen-presenting cells.

Answer 147

blood monocytes

Question 148

Nuclei of microglial cells can often be recognized in routine ______ preparations by their small, dense, slightly elongated structure, which contrasts with the larger, spherical, more lightly stained nuclei of other glial cells.

Answer 148

hematoxylin and eosin (H&E)

Question 149

______ using antibodies against cell surface antigens of immune cells demonstrates microglial processes.

Answer 149

Immunohistochemistry

Question 150

When activated by damage or microorganisms microglia retract their processes, proliferate, and assume the morphologic characteristics and functions of ______ cells.

Answer 150

antigen-presenting

Question 151

______ (named for 19th century German histologist ______), sometimes called ______, are found only in the PNS and differentiate from precursors in the neural crest.

Answer 151

Schwann cells, Theodor Schwann, neurolemmocytes

Question 152

Schwann cells are the counterparts to ______ of the CNS, having trophic interactions with axons and most importantly forming their ______.

Answer 152

oligodendrocytes, myelin sheathes

Question 153

However unlike an oligodendrocyte, a Schwann cell forms myelin around a portion of only ______ axon.

Answer 153

one

Question 154

Also derived from the embryonic neural crest, small ______ form a thin, intimate glial layer around each large neuronal cell body in the ganglia of the PNS.

Answer 154

satellite cells

Question 155

______ exert a trophic or supportive effect on these neurons, insulating, nourishing, and regulating their microenvironments.

Answer 155

Satellite cells

Question 156

The major structures comprising the CNS are the ______, ______, and ______.

Answer 156

cerebrum, cerebellum, spinal cord

Question 157

The CNS is completely covered by connective tissue layers, the ______, but CNS tissue contains very little ______ or similar material, making it relatively soft and easily damaged by injuries affecting the protective skull or vertebral bones.

Answer 157

meninges, collagen

Question 158

Most ______ neurons and their functional organization are more appropriately covered in neuroscience rather than histology courses, but certain important cells and basic topics will be introduced here.

Answer 158

CNS

Question 159

Many structural features of ______ tissues can be seen in unstained, freshly dissected specimens.

Answer 159

CNS

Question 160

Central Nervous System

Many regions show organized areas of ______ and ______, differences caused by the differential distribution of lipid-rich myelin.

Answer 160

white matter, gray matter

Question 161

Central Nervous System

The main components of white matter are myelinated ______, often grouped together as ______, and the myelin-producing ______.

Answer 161

axons, tracts, oligodendrocytes

Question 162

Central Nervous System

______ and ______ are also present, but very few ______ cell bodies.

Answer 162

Astrocytes, microglia, neuronal

Question 163

Central Nervous System

______ contains abundant neuronal cell bodies, dendrites, astrocytes, and microglial cells, and is where most synapses occur.

Answer 163

Gray matter

Question 164

Central Nervous System

______ makes up the thick cortex or surface layer of both the cerebrum and the cerebellum; most ______ is found in deeper regions.

Answer 164

Gray matter, white matter

Question 165

Central Nervous System

Deep within the brain are localized, variously shaped darker areas called the ______, each containing large numbers of aggregated neuronal cell bodies.

Answer 165

cerebral nuclei

Question 166

In the folded ______, neuroscientists recognize six layers of neurons with different sizes and shapes. The most conspicuous of these cells are the efferent ______. Neurons of the cerebral cortex function in the integration of sensory information and the initiation of voluntary motor responses.

Answer 166

cerebral cortex, pyramidal neurons

Question 167

The sharply folded ______ coordinates muscular activity throughout the body and is organized with three layers.

Answer 167

cerebellar cortex

Question 168

The sharply folded cerebellar cortex coordinates muscular activity throughout the body and is organized with three layers:

Answer 168

molecular layer
Purkinje cells
granular layer

Question 169

The sharply folded cerebellar cortex coordinates muscular activity throughout the body and is organized with three layers:

■ A thick outer ______ has much neuropil and scattered neuronal cell bodies.

Answer 169

molecular layer

Question 170

The sharply folded cerebellar cortex coordinates muscular activity throughout the body and is organized with three layers:

■ A thin middle layer consists only of very large neurons called ______ (named for the 19th century Czech histologist ______). These are conspicuous even in H&E-stained sections, and their dendrites extend throughout the molecular layer as a branching basket of nerve fibers.

Answer 170

Purkinje cells, Jan Purkinje

Question 171

The sharply folded cerebellar cortex coordinates muscular activity throughout the body and is organized with three layers:

■ A thick inner ______ contains various very small, densely packed neurons (including granule cells, with diameters of only ______-______ μm) and little neuropil.

Answer 171

granular layer, 4, 5

Question 172

In cross sections of the spinal cord, the white matter is ______ and the gray matter forms a ______, ______ mass.

Answer 172

peripheral, deeper, H-shaped

Question 173

The two anterior projections of this gray matter, the ______, contain cell bodies of very large motor neurons whose axons make up the ventral roots of spinal nerves.

Answer 173

anterior horns

Question 174

The two ______ contain interneurons which receive sensory fibers from neurons in the spinal (dorsal root) ganglia.

Answer 174

posterior horns

Question 175

Near the middle of the cord the gray matter surrounds a small ______, which develops from the lumen of the neural tube, is continuous with the ventricles of the brain, is lined by ependymal cells, and contains CSF.

Answer 175

central canal

Question 176

The skull and the vertebral column protect the CNS, but between the bone and nervous tissue are membranes of connective tissue called the ______.

Answer 176

meninges

Question 177

Three meningeal layers are distinguished: the ______,
______, and ______ maters.

Answer 177

dura, arachnoid, pia

Question 178

Three meningeal layers are distinguished:

The thick external ______ consists of dense irregular connective tissue organized as an outer periosteal layer continuous with the periosteum of the skull and an inner meningeal layer.

Answer 178

dura mater

Question 179

Three meningeal layers are distinguished:

These two layers are usually fused, but along the superior sagittal surface and other specific areas around the brain they separate to form the blood-filled ______.

Answer 179

dural venous sinuses

Question 180

Around the spinal cord the dura mater is separated from the periosteum of the vertebrae by the ______, which contains a plexus of thin- walled veins and loose connective tissue.

Answer 180

epidural space

Question 181

The dura mater may be separated from the arachnoid by formation of a thin ______.

Answer 181

subdural space

Question 182

The arachnoid (Gr. arachnoeides, spider web-like) has two components:

Answer 182

(1) a sheet of connective tissue in contact with the dura mater
(2) a system of loosely arranged trabeculae composed of collagen and fibroblasts, continuous with the underlying pia mater layer.

Question 183

Arachnoid

Surrounding these trabeculae is a large, sponge-like cavity, the ______, filled with ______.

Answer 183

subarachnoid space, CSF

Question 184

Arachnoid

______
- This fluid-filled space helps cushion and protect the CNS from minor trauma.

Answer 184

subarachnoid space

Question 185

Arachnoid

The ______ communicates with the ventricles of the brain where the CSF is produced.

Answer 185

subarachnoid space

Question 186

The connective tissue of the arachnoid is said to be ______ because it lacks nutritive capillaries, but larger blood vessels run through it.

Answer 186

avascular

Question 187

Because the arachnoid has fewer ______ in the spinal cord, it can be more clearly distinguished from the pia mater in that area.

Answer 187

trabeculae

Question 188

The arachnoid and the pia mater are intimately associated and are often considered a single membrane called the ______.

Answer 188

pia-arachnoid

Question 189

In some areas, the ______ penetrates the dura mater and protrudes into blood-filled dural venous sinuses located there.

Answer 189

arachnoid

Question 190

Arachnoid

These CSF-filled protrusions, which are covered by the vascular endothelial cells lining the sinuses, are called ______ and function as sites for absorption of CSF into the blood of the venous sinuses.

Answer 190

arachnoid villi

Question 191

The innermost ______ mater consists of flattened, mesenchymally derived cells closely applied to the entire surface of the CNS tissue.

Answer 191

pia

Question 192

The pia does not directly contact nerve cells or fibers, being separated from the neural elements by the very thin superficial layer of ______ (the ______, or ______), which adheres firmly to the pia mater.

Answer 192

astrocytic processes, glial limiting membrane, glia limitans

Question 193

Together, the ______ and the layer of ______ form a physical barrier separating CNS tissue from CSF in the subarachnoid space.

Answer 193

pia mater, astrocytic end feet

Question 194

Blood vessels penetrate CNS tissue through long ______ covered by pia mater, although the pia disappears when the blood vessels branch to form the small capillaries.

However, these capillaries remain completely covered by the ______ of ______ processes.

Answer 194

perivascular spaces, perivascular layer, astrocytic

Question 195

The ______ is a functional barrier that allows much tighter control than that in most tissues over the passage of substances moving from blood into the CNS tissue.

Answer 195

blood-brain barrier (BBB)

Question 196

The main structural component of the BBB is the ______, in which the cells are tightly sealed together with well-developed occluding junctions, with little or no transcytosis activity, and surrounded by the basement membrane.

Answer 196

capillary endothelium

Question 197

The ______ that envelops the basement membrane of capillaries in most CNS regions contributes to the BBB and further regulates passage of molecules and ions from blood to brain.

Answer 197

limiting layer of perivascular astrocytic feet

Question 198

The ______ protects neurons and glia from bacterial toxins, infectious agents, and other exogenous substances, and helps maintain the stable composition and constant balance of ions in the interstitial fluid required for normal neuronal function.

Answer 198

BBB

Question 199

The BBB is not present in regions of the ______ where plasma components are monitored, in the ______ which releases hormones, or in the ______ where CSF is produced.

Answer 199

hypothalamus, posterior pituitary, choroid plexus

Question 200

The ______ consists of highly vascular tissue, elaborately folded and projecting into the large ventricles of the brain.

Answer 200

choroid plexus

Question 201

______
- It is found in the roofs of the third and fourth ventricles and in parts of the two lateral ventricular walls, all regions in which the ependymal lining directly contacts the pia mater.

Answer 201

Choroid Plexus

Question 202

Each villus of the choroid plexus contains a thin layer of well-vascularized ______ covered by ______.

Answer 202

pia mater, cuboidal ependymal cells

Question 203

The function of the choroid plexus is to remove water from blood and release it as the ______.

Answer 203

CSF

Question 204

______ is clear, contains Na+, K+, and Cl– ions but very little protein, and its only cells are normally very sparse lymphocytes.

Answer 204

CSF

Question 205

______
- It is produced continuously and it completely fills the ventricles, the central canal of the spinal cord, the subarachnoid and perivascular spaces.

Answer 205

CSF

Question 206

______
- It provides the ions required for CNS neuronal activity and in the arachnoid serves to help absorb mechanical shocks.

Answer 206

CSF

Question 207

______ provide the main pathway for absorption of CSF back into the venous circulation.

Answer 207

Arachnoid villi

Question 208

There are very few ______ vessels in CNS tissue.

Answer 208

lymphatic

Question 209

The main components of the peripheral nervous system (PNS) are the ______, ______, and ______.

Answer 209

nerves, ganglia, nerve endings

Question 210

______ are bundles of nerve fibers (______) individually surrounded by ______ and ______.

Answer 210

Peripheral nerves, axons, Schwann cells, connective tissue

Question 211

______ are analogous to tracts in the CNS, containing axons enclosed within sheaths of glial cells specialized to facilitate axonal function.

Answer 211

Nerves

Question 212

In peripheral nerves, axons are sheathed by ______ or ______.

Answer 212

Schwann cells, neurolemmocytes

Question 213

Peripheral Nervous System

The sheath may or may not form ______ around the axons, depending on their ______.

Answer 213

myelin, diameter

Question 214

As axons of large diameter grow in the PNS, they are engulfed along their length by a series of differentiating neurolemmocytes and become ______.

Answer 214

myelinated nerve fibers

Question 215

Myelinated Fibers

The plasma membrane of each covering Schwann cell fuses with itself at an area termed the ______ and a wide, flattened process of the cell continues to extend itself, moving circumferentially around the axon many times.

Answer 215

mesaxon

Question 216

Myelinated Fibers

The multiple layers of Schwann cell membrane unite as a thick ______.

Answer 216

myelin sheath

Question 217

Myelinated Fibers

Composed mainly of lipid bilayers and membrane proteins, ______ is a large lipoprotein complex that, like cell membranes, is partly removed by standard histologic procedures.

Answer 217

myelin

Question 218

Myelinated Fibers

Unlike oligodendrocytes of the CNS, a Schwann cell forms myelin around only a portion of ______ axon.

Answer 218

one

Question 219

Myelinated Fibers

With high-magnification TEM, the ______ appears as a thick electron-dense axonal covering in which the concentric membrane layers may be visible.

Answer 219

myelin sheath

Question 220

Myelinated Fibers

The prominent electron-dense layers visible ultrastructurally in the sheath, the ______, represent the fused, protein-rich cytoplasmic surfaces of the Schwann cell membrane.

Answer 220

major dense lines

Question 221

Myelinated Fibers

Along the myelin sheath, these surfaces periodically separate slightly to allow transient movement of cytoplasm for membrane maintenance; at these ______ (or ______) the major dense lines temporarily disappear.

Answer 221

myelin clefts, Schmidt-Lanterman clefts

Question 222

Myelinated Fibers

Faintly seen ultrastructurally in the light staining layers are the ______ that represent the apposed outer bilayers of the Schwann cell membrane.

Answer 222

intraperiod lines

Question 223

Myelinated Fibers

Membranes of Schwann cells have a higher proportion of ______ than do other cell membranes, and the ______ serves to insulate axons and maintain a constant ionic microenvironment most suitable for action potentials.

Answer 223

lipids, myelin sheath

Question 224

Myelinated Fibers

Between adjacent Schwann cells on an axon the
myelin sheath shows small ______ (or ______), where the axon is only partially covered by interdigitating Schwann cell processes.

Answer 224

nodes of Ranvier, nodal gaps

Question 225

Myelinated Fibers

At these nodes the axolemma is exposed to ions in
the interstitial fluid and has a much higher concentration of voltage-gated Na+ channels, which renew the action potential and produce ______ of nerve impulses, their rapid movement from node to node.

Answer 225

saltatory conduction

Question 226

Myelinated Fibers

• The length of axon ensheathed by one Schwann cell, the ______, varies directly with axonal diameter and ranges from ______ to ______ μm.

Answer 226

internodal segment, 300, 1500

Question 227

______
- Unlike the CNS where many short axons are not myelinated at all but course among other neuronal and astrocytic processes, the smallest diameter axons of peripheral nerves are still enveloped within simple folds of Schwann cells.

Answer 227

Unmyelinated fibers

Question 228

These very small ______ do not however undergo multiple wrapping to form a myelin sheath.

Answer 228

unmyelinated fibers

Question 229

In ______ nerves each Schwann cell can enclose portions of many axons with small diameters.

Answer 229

unmyelinated

Question 230

Without the thick myelin sheath, ______ are not seen along unmyelinated nerve fibers.

Answer 230

nodes of Ranvier

Question 231

Unmyelinnated fibers

Moreover, these small-diameter axons have evenly distributed voltage-gated ion channels; their impulse conduction is not ______ and is ______ slower than that of myelinated axons.

Answer 231

saltatory, much

Question 232

In the PNS, nerve fibers are grouped into bundles to form ______.

Answer 232

nerves

Question 233

Except for very thin nerves containing only unmyelinated fibers, nerves have a ______, ______ appearance because of their ______ and ______ content.

Answer 233

whitish, glistening, myelin, collagen

Question 234

______ and ______ are enclosed within layers of connective tissue.

Answer 234

Axons, Schwann cells

Question 235

Immediately around the external lamina of the Schwann cells is a thin layer called the ______, consisting of reticular fibers, scattered fibroblasts, and capillaries.

Answer 235

endoneurium

Question 236

Groups of axons with Schwann cells and endoneurium are bundled together as ______ by a sleeve of ______, containing flat fibrocytes with their edges sealed together by tight junctions.

Answer 236

fascicles, perineurium

Question 237

From two to six layers of these unique connective tissue cells regulate diffusion into the fascicle and make up the ______ which helps maintain the fibers’ microenvironment.

Answer 237

blood-nerve barrier

Question 238

Externally, peripheral nerves have a dense, irregular fibrous coat called the ______, which extends deeply to fill the space between fascicles.

Answer 238

epineurium

Question 239

______ nerves establish communication between centers in the CNS and the sense organs and effectors (muscles, glands, etc).

They generally contain both ______ and ______ fibers.

Answer 239

Peripheral, afferent, efferent

Question 240

Peripheral nerves establish communication between centers in the CNS and the sense organs and effectors (muscles, glands, etc).

They generally contain both afferent and efferent fibers.
• ______ fibers carry information from internal body regions and the environment to the CNS.

Answer 240

Afferent

Question 241

Peripheral nerves establish communication between centers in the CNS and the sense organs and effectors (muscles, glands, etc).

They generally contain both afferent and efferent fibers.
• ______ fibers carry impulses from the CNS to effector organs commanded by these centers.

Answer 241

Efferent

Question 242

Nerves possessing only sensory fibers are called ______.

Answer 242

sensory nerves

Question 243

Those composed only of fibers carrying impulses to the effectors are called ______.

Answer 243

motor nerves

Question 244

Most nerves have both sensory and motor fibers and are called ______, usually also with both ______ and ______ axons.

Answer 244

mixed nerves, myelinated, unmyelinated

Question 245

Very small nerves consist of one ______.

Answer 245

fascicle

Question 246

______ nerves can be found in sections of many organs and often show a winding disposition in connective tissue.

Answer 246

Small

Question 247

______ are typically ovoid structures containing ______ cell bodies and their surrounding ______ satellite cells supported by delicate connective tissue and surrounded by a denser capsule.

Answer 247

Ganglia, neuronal, glial

Question 248

Ganglia

Because they serve as relay stations to transmit nerve impulses, at least one nerve ______ and another ______ from each ganglion.

Answer 248

enters, exits