MIDTERM: NERVOUS TISSUE Flashcards
consisting of the brain
and spinal cord
Central nervous system (CNS
composed of
the cranial, spinal, and peripheral nerves conducting
impulses to and from the CNS (sensory and motor
nerves, respectively) and ganglia that are small aggregates of nerve cells outside the CNS.
Peripheral nervous system (PNS)
sensory input perceived consciously (eg, from
eyes ears, skin, and musculoskeletal structures)
A. Somatic
sensory input not perceived consciously (eg,
from internal organs and cardiovascular structures)
B. Visceral
motor output controlled consciously or voluntarily (eg, by skeletal muscle effectors)
A. Somatic
motor output not controlled consciously (eg,
by heart or gland effectors)
B. Autonomic
efferent
Motor division
afferent
Sensory division
The autonomic motor nerves, comprising what is often called
the
autonomic nervous system (ANS)
each with one axon and two or
more dendrites, are the most common
Multipolar neurons
, with one dendrite and one axon,
comprise the sensory neurons of the retina, the olfactory
epithelium, and the inner ear.
Bipolar neurons
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.
Unipolar or pseudounipolar neurons
with many dendrites but no true
axon, do not produce action potentials, but regulate electrical changes of adjacent CNS neurons.
Anaxonic neurons,
which contains the nucleus and most of the cell’s organelles and serves as the synthetic or trophic center for the
entire neuron
cell body
which are the numerous elongated processes extending from the perikaryon and specialized to
receive stimuli from other neurons at unique sites called
synapses.
dendrites
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). Axons may also receive information from
other neurons, information that mainly modifies the
transmission of action potentials to those neurons.
axon
establish relationships among other neurons, forming complex functional networks or circuits in
the CNS.
Interneurons
Histologically these regions with
concentrated RER and other polysomes are basophilic and
are distinguished as
chromatophilic substance (or Nissl
substance, Nissl bodies)
is often large, with a large,
euchromatic nucleus and well-developed nucleolus.
cell body
A “typical” neuron has three major parts:
The cell body
Numerous short (dendrites)
A long (axon)
carries impulses from the cell body and
is covered by a myelin sheath composed of other cells.
axon
extend from the perikaryon, receiving input from other
neurons.
Numerous short dendrites
are typically short, small processes emerging and branching off the soma
Dendrites
Most neurons have only _____ axon, typically longer than its
dendrites.
Axons
The plasma membrane of the axon is often called the ________ and its contents are known as _________
axolemma / axoplasm
Axons originate from a pyramid-shaped region of the
perikaryon called the
axon hillock
support neuronal survival and activities, and are
10 times more abundant than neurons in the mammalian
brain.
Glial cells
. Fibrous astrocytes, with long delicate processes, are
abundant in white matter; those with many shorter processes
are called
protoplasmic astrocytes
wrap processes around portions of axons in
the CNS, forming myelin sheaths that insulate the axons and
facilitate nerve impulses.
Oligodendrocytes
the most numerous cell of the CNS, all produce hundreds of processes to cover and provide regulated microenvironments for neuronal perikarya, synapses, and capillaries.
Astrocytes
are epithelial-like cells, lacking basement
membranes, which line the fluid-filled cerebral ventricles and
central canal of the spinal cord.
Ependymal cells
a differs from all other glial cells in originating from
blood monocytes, not from neural tissue precursors; they mediate immune defense activity within the CNS
Microglia
enclose all axons in nerves
of the PNS, producing myelin sheaths around large-diameter
axons, whose impulse conductivity is augmented at the nodes
of Ranvier between successive Schwann cells.
Schwann cells (neurolemmocytes)
are located within PNS ganglia, aggregated sensory or autonomic neuronal cell bodies, where they enclose
each perikaryon and regulate its microenvironment.
Satellite cells
is a thin connective tissue layer immediately surrounding Schwann cells in peripheral nerves, containing a few nonfenestrated capillaries and much reticulin.
Endoneurium
which can be either sensory or autonomic, contain neuronal cell bodies and their satellite cells and are surrounded by connective tissue continuous with that of nerves.
Ganglia,
characterize the cortex of the cerebellum, and
layers of small pyramidal neurons form the cerebral cortex
Purkinje neurons
- Which of the following is characteristic of the chromatophilic
material called Nissl substance in neural tissue?
a. Found throughout neurons
b. Site of mRNA translation for proteins of the axolemma
c. Most abundant in unipolar neurons
d. Becomes more abundant as an individual gets older
e. An example of intermediate filament proteins
b
The human nervous system, by far the most complex system in the body, is formed by a network of many billion
nerve cells (neurons), all assisted by many more supporting cells called
glial cells
is a slowly progressing disorder affecting
muscular activity characterized by tremors, reduced activity
of the facial muscles, loss of balance, and postural stiffness.
Parkinson disease
It is caused by gradual loss by apoptosis of dopamineproducing neurons whose cell bodies lie within the nuclei
of the CNS substantia nigra.
Parkinson disease
is treated
with l-dopa (l-3,4-dihydroxyphenylalanine), a precursor of
dopamine that augments the declining production of this
neurotransmitter.
Parkinson disease
autonomic nervous system (ANS), all have pathways involving
two neurons: a
preganglionic neuron
postganglionic neuron
with the cell body in the CNS
preganglionic neuron
with the cell body in a ganglion.
postganglionic neuron
The
ANS has two divisions:
parasympathetic division
sympathetic division
with its
ganglia within or near the effector organs, maintains normal body
homeostasis
.parasympathetic division,
has its ganglia close to
the CNS and controls the body’s responses during emergencies and
excitement
sympathetic division
ANS components located in the wall of the digestive
tract are sometimes referred to as the
enteric nervous system
As the neural tube detaches from the now overlying ectoderm,
many cells separate from it and produce a mass of mesenchymal
cells called the
neural crest
Histologically these regions with
concentrated RER and other polysomes are basophilic and
are distinguished as
chromatophilic substance (or Nissl
substance, Nissl bodies)
Cells in both central and peripheral nerve tissue are of
two kinds:
neurons
glial cells
which typically have numerous long
processes
neurons
which have
short processes, support and protect neurons, and participate
in many neural activities, neural nutrition, and defense of cells
in the CNS
glial cells
is capable of traveling long distances
along neuronal processes, transmitting such signals to other
neurons, muscles, and glands.
action potential, the depolarization wave,
or the nerve impulse, i
The functional unit in both the CNS and PNS is the
neuron
Some neuronal components have special names, such as
“neurolemma”
A “typical” neuron has three major parts
cell body
dendrites
axon
(also called the perikaryon or soma) is often large, with a large,
euchromatic nucleus and well-developed nucleolus. The cytoplasmic contains basophilic Nissl substance or Nissl bodies,
which are large masses of free polysomes and RER indicating
the cell’s high rate of protein synthesis.
cell body
extend from the perikaryon, receiving input from other
neurons.
Numerous short dendrites
carries impulses from the cell body and
is covered by a myelin sheath composed of other cells. The ends
of axons usually have many small branches (telodendria), each
of which ends in a knob-like structure that forms part of a functional connection (synapse) with another neuron or other cell.
A long axon
latter formed by unique protein subunits and called ______ in this cell type.
neurofilaments
are typically short, small processes emerging and branching off the soma (Figure 9–3).
Usually covered with many synapses, dendrites are the principal
signal reception and processing sites on neurons.
Dendrites (Gr. dendron, tree)
In the
CNS most synapses on dendrites occur on _________ which are dynamic membrane protrusions along the small
dendritic branches, visualized with silver staining and studied by confocal or electron microscopy
dendritic spines
serve as the initial processing sites for synaptic signals
and occur in vast numbers, estimated to be on the order of 1014
for cells of the human cerebral cortex
Dendritic
spines
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.
neural plasticity
Most neurons have only one _______ typically longer than its
dendrites.
axon
The plasma membrane of the axon is often called the ________
axolemma
The plasma membrane of the axon is often called the ________ and its contents are known as ________
axolemma
axoplasm
Axons originate from a pyramid-shaped region of the
perikaryon called the ________
axon hillock
travels along
an axon like a spark moves along an explosive’s fuse
nerve impulse, or an action potential
The action potential is propagated along
the axon as a wave of membrane depolarization produced by
__________ in the axolemma that
allow diffusion of these ions into and out of the axoplasm
voltage-gated Na+ and K+ channels
Axons generally branch less profusely than dendrites,
but do undergo ________
terminal arborization
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.
collaterals
which are the numerous elongated processes extending from the perikaryon and specialized to
receive stimuli from other neurons at unique sites
synapses
Each
small axonal branch ends with a dilation called _________ that contacts another neuron or
non-nerve cell at a synapse to initiate an impulse in that cell.
terminal bouton
Organelles and macromolecules
synthesized in the cell body move by ________ t along axonal microtubules via _______ from the perikaryon to the synaptic terminals.
anterograde transport
kinesin
_______ 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.
Retrograde transport
dynein
This difference is the axon’s
resting potential
are low-molecular-weight molecules
that bind to the voltage-gated sodium channels of the axolemma, interfering with sodium ion influx and, consequently,
inhibiting the action potential responsible for the nerve
impulse.
local anesthetics
_________ are sites where nerve impulses
are transmitted from one neuron to another, or from neurons
and other effector cells
Synapses (Gr. synapsis, union)
Synapses convert
an electrical signal (nerve impulse) from the _______ into a chemical signal that affects the _________
presynaptic
cell
postsynaptic cell
Most synapses act by releasing_______ which
are usually small molecules that bind specific receptor proteins to either open or close ion channels or initiate secondmessenger cascades.
neurotransmitters
cell bodies can be very large and can be measure upto ______
150 um
are sites where nerve impulses
are transmitted from one neuron to another, or from neurons
and other effector cells
Synapses
contains receptors for the neurotransmitter, and ion channels or other
mechanisms to initiate a new impulse
postsynaptic cell membrane
contains mitochondria and numerous synaptic vesicles
from which neurotransmitter is released by exocytosis
presynaptic axon terminal (terminal bouton)
A 20- to 30-nm-wide intercellular space called the
synaptic cleft
Neurotransmitters from ________ cause
postsynaptic Na+ channels to open, and the resulting Na
excitatory synapses
_______ neurotransmitters open Cl–
or other anion channels, causing influx of anions and _________ of the postsynaptic cell, making its
membrane potential more negative and more resistant to
depolarization.
inhibitory synapses /
hyperpolarization
The chemical transmitter used at neuromuscular junctions
and some synapses of the CNS is ________
acetylcholine
________ such as glutamate and γ-aminobutyrate (GABA)
amino acids
_______ such as serotonin (5-hydroxytryptamine
or 5-HT) and ______ such as dopamine, all of
which are synthesized from amino acids
Monoamines / catecholamines
______ such as endorphins and substance
Small polypeptides
Within the
CNS other major categories of neurotransmitters include the
following
amino acids
Monoamines and catecholamines
polypeptides
______ support neuronal survival and activities, and are
10 times more abundant than neurons in the mammalian
brain.
Glial cells
Proximal regions of the astrocytic
processes are reinforced with bundles of intermediate filaments
made of _______
glial fibrillary acid protein (GFAP),
_______ with long delicate processes, are
abundant in white matter; those with many shorter processes
are called _______
Fibrous astrocytes
protoplasmic astrocytes
_________ a widely used class of drugs for treatment of depression and anxiety disorders, were designed to
augment levels of this neurotransmitter at the postsynaptic
membrane of serotonergic CNS synapses by specifically
inhibiting its reuptake at the presynaptic membrane.
Selective serotonin reuptake
inhibitors (SSRIs)
Most brain tumors are _______ derived from fibrous
astrocytes. These are distinguished pathologically by their
expression of GFAP.
astrocytomas
Chemical structure significantly different from that of other neurotransmitters; active in
CNS and in both somatic and autonomic parts of PNS; binds to ACh receptors (cholinergic
receptors) in PNS to open ion channels in postsynaptic membrane and stimulate muscle
contraction
ACETYLCHOLINE (ACh)
Molecules with both carboxyl (—COOH) and amine (—NH2
) groups and various R groups;
act as important transmitters in the CNS
AMINO ACIDS
Excites activity in neurons to promote cognitive function in the brain (learning and memory);
most common neurotransmitter in the brain; opens Na+ channels
Glutamate
Synthesized from glutamate; primary inhibitory neurotransmitter in the brain; also influences
muscle tone; opens or closes various ion channels
Gamma-aminobutyric acid (GABA)
Inhibits activity between neurons in the CNS, including retina; opens Cl–
channels
Glycine
Molecules synthesized from an amino acid by removing the carboxyl group and retaining the
single amine group; also called biogenic amines
MONOAMINES
Has various functions in the brain related to sleep, appetite, cognition (learning, memory), and
mood; modulates actions of other neurotransmitters
Serotonin or 5-hydroxytryptamine (5-HT)
A distinct group of monoamines
Catecholamines
Produces inhibitory activity in the brain; important roles in cognition (learning, memory),
motivation, behavior, and mood; opens K+ channels, closes Ca2+ channels
Dopamine
Neurotransmitter of PNS (sympathetic division of autonomic nervous system) and specific
CNS regions
Norepinephrine (noradrenaline)
Has various effects in the CNS, especially the spinal cord, thalamus, and hypothalamus
Epinephrine (adrenaline)
Small polypeptides act as signals to assist in and modulate communication among neurons in
the CNS
NEUROPEPTIDES
Helps regulate response to noxious and potentially harmful stimuli
Enkephalin
Involved in memory regulation and energy balance (increased food intake and decreased
physical activity)
Neuropeptide Y
Inhibits activities of neurons in specific brain areas
Somatostatin
Assists with pain information transmission into the brain
Substance P
Stimulates neurons in the brain to help mediate satiation (fullness) and repress hunger
Cholecystokinin (CCK)
Prevents release of pain signals from neurons and fosters a feeling of well-being
Beta-endorphin
Helps control and moderate the effects of dopamine
Neurotensin
Also part of a nucleotide, inhibits activities in certain CNS neurons
Adenosine
Involved in learning and memory; relaxes muscle in the digestive tract; important for
relaxation of smooth muscle in blood vessels (vasodilation)
Nitric oxide
Extending fibrous processes with expanded ___________ that cover capillary endothelial cells and
modulate blood flow and help move nutrients, wastes,
and other metabolites between neurons and capillaries
perivascular feet
Forming a barrier layer of expanded protoplasmic processes, called the ____________ which lines
the meninges at the external CNS surface
glial limiting membrane
Filling tissue defects after CNS injury by proliferation to
form an
astrocytic scar.
Oligodendrocyte
- Origin
-location
- Main functions
-Neural tube
-CNS
-Myelin production, electrical insulation
Astrocyte
- Origin
-location
- Main functions
-Neural tube
-CNS
-Structural and metabolic support of
neurons, especially at synapses; repair
processes
Ependymal cell
- Origin
-location
- Main functions
-Neural tube
- Line ventricles and central
canal of CNS
-Aid production and movement of CSF
Microglia
- Origin
-location
- Main functions
-Bone marrow (monocytes)
-CNS
-Defense and immune-related activities
Schwann cell
- Origin
-location
- Main functions
-Neural crest
-Peripheral nerves
-Myelin production, electrical insulation
Satellite cells (of ganglia)
-Neural crest
-Peripheral ganglia
-Structural and metabolic support for
neuronal cell bodies
a common type of dementia in the
elderly, affects both neuronal perikarya and synapses within
the cerebrum.
Alzheimer disease
. Functional defects are due to ______which are accumulations of tau protein associated
with microtubules of the neuronal perikaryon and axon hillock regions, and ______ which are dense aggregates of β-amyloid protein that form around the outside of
these neuronal regions.
neurofibrillary
tangles, neuritic plaques
_____ are columnar or cuboidal cells that line the
fluid-filled ventricles of the brain and the central canal of the
spinal cord
Ependymal cells
_______ are
small cells with actively mobile processes evenly distributed
throughout gray and white matter
microglia
_____ are monocyte-derived, antigen-presenting cells of the
CNS, less numerous than astrocytes but nearly as common as
neurons and evenly distributed in both gray and white matter
Microglia
_____ sometimes called neurolemmocytes,
are found only in the PNS and differentiate from precursors in the neural crest.
Schwann cells
Schwann cells are the counterparts
to oligodendrocytes of the CNS, having trophic interactions
with axons and most importantly forming their ______
myelin
sheathes.
Also derived from the embryonic neural crest, small ______ s form a thin, intimate glial layer around each large
neuronal cell body in the ganglia of the PNS
satellite cells
In the _____ the myelin sheaths surrounding axons are damaged by an autoimmune mechanism
that interferes with the activity of the affected neurons and
produces various neurologic problems.
multiple sclerosis
The major structures comprising the CNS are the ____
cerebrum,
cerebellum, and spinal cord
Many regions show
organized areas of ________, differences caused by the differential distribution of lipid-rich
myelin
white matter and gray matter
Deep within the brain are localized,
variously shaped darker areas called the ______ each
containing large numbers of aggregated neuronal cell bodies
cerebral nuclei
In the folded ______ neuroscientists recognize
six layers of neurons with different sizes and shapes.
cerebral cortex,
The most
conspicuous of these cells are the efferent ______
pyramidal neurons
The sharply folded cerebellar cortex coordinates muscular activity throughout the body and is organized with three
layers:
molecular layer
Purkinje cells
granular layer
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.
anterior horns
The two ______ contain interneurons which
receive sensory fibers from neurons in the spinal (dorsal root)
ganglia.
posterior horns
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
central canal
The skull and the vertebral column protect the CNS, but
between the bone and nervous tissue are membranes of
connective tissue called the
meninges
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
dura mater
____ has two
components: (1) a sheet of connective tissue in contact with
the dura mater and (2) a system of loosely arranged trabeculae composed of collagen and fibroblasts, continuous with the
underlying pia mater layer
arachnoid
Surrounding these trabeculae is a
large, sponge-like cavity, the _____filled with
CSF
subarachnoid space
Around the spinal cord
the dura mater is separated from the periosteum of the vertebrae by the _____ which contains a plexus of thinwalled veins and loose connective tissue
epidural space
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 ____
dural venous sinuses
covered by the vascular endothelial cells lining the sinuses, are _____ and function as sites for absorption of
CSF into the blood of the venous sinuses.
arachnoid villi
_____ consists of flattened, mesenchymally derived cells closely
applied to the entire surface of the CNS tissue.
pia matter
_____ 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.
blood-brain barrier (BBB)
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
capillary endothelium
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
perivascular spaces
the ______ consists of highly vascular tissue, elaborately folded and projecting into the large ventricles of the
brain.
choroid plexus
A decrease in the absorption of CSF or a blockage of outflow
from the ventricles during fetal or postnatal development
results in the condition known as _______which promotes a progressive
enlargement of the head followed by mental impairment.
hydrocephalus
A decrease in the absorption of CSF or a blockage of outflow
from the ventricles during fetal or postnatal development
results in the condition known as _______which promotes a progressive
enlargement of the head followed by mental impairment.
hydrocephalus
______ are analogous to tracts in the CNS, containing axons
enclosed within sheaths of glial cells specialized to facilitate
axonal function.
nerves
In peripheral nerves, axons are sheathed by _______
Schwann cells or neurolemmocytes
The multiple layers of Schwann cell membrane unite as a thick _____
myelin sheath
As axons of large diameter grow in the PNS, they are engulfed
along their length by a series of differentiating neurolemmocytes and become _____
myelinated nerve fibers
The main components of the peripheral nervous system (PNS)
are the ____
nerves, ganglia, and nerve endings
Along the myelin sheath, these surfaces periodically
separate slightly to allow transient movement of cytoplasm for
membrane maintenance; at these _____
myelin clefts
The
prominent electron-dense layers visible ultrastructurally
in the sheath, the ____
major dense lines
Between
adjacent Schwann cells on an axon the myelin sheath shows
small _____, where the axon is only partially covered by
interdigitating Schwann cell processes
nodes of Ranvier
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
saltatory conduction
The length of axon ensheathed
by one Schwann cell, the _____ varies directly
with axonal diameter and ranges from 300 to 1500 μm
internodal segment,
These
very small ____do not however undergo
multiple wrapping to form a myelin sheath
In unmyelinated nerves each Schwann cell can enclose portions of many axons with small diameters.
unmyelinated fibers
The axon
is enveloped by the myelin sheath, which, in addition to membrane, contains some Schwann cell cytoplasm in spaces called ______ between the major dense
lines of membranes
Schmidt-Lanterman or myelin clefts
Immediately around the external lamina of the Schwann cells is a
thin layer called the _____
endoneurium
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
fascicles / perineurium
From
two to six layers of these unique connective tissue cells regulate diffusion into the fascicle and make up the _____
blood-nerve
barrier
helps maintain the fibers’ microenvironment.
Externally, peripheral nerves have a dense, irregular fibrous
coat called the ____ which extends deeply to fill the
space between fascicles.
epineurium
fibers carry information from internal body
. Afferent
fibers
carry impulses from the CNS to effector organs commanded
by these centers.
Efferent
Nerves possessing only sensory fibers are
called ______
sensory nerves
those composed only of fibers carrying impulses to the effectors are called
motor nerves
Most
nerves have both sensory and motor fibers and are called _______, usually also with both myelinated and unmyelinated axons.
mixed nerves
are typically ovoid structures containing neuronal
cell bodies and their surrounding glial satellite cells supported by delicate connective tissue and surrounded by a
denser capsule
Ganglia
The direction of the nerve impulse
determines whether the ganglion will be a ____ or ____
sensory or an
autonomic ganglion
The large neuronal cell bodies of ganglia
(Figure 9–29) are associated with thin, sheetlike extensions of
small glial _____
satellite cells
______ are small bulbous dilations in autonomic nerves, usually with multipolar neurons.
Autonomic ganglia
Some are
located within certain organs, especially in the walls of the
digestive tract, where they constitute the _____
intramural ganglia
____nerves effect the
activity of smooth muscle, the secretion of some glands, heart
rate, and many other involuntary activities by which the body
maintains a constant internal environment (homeostasis).
Autonomic
This neural plasticity and reformation of processes are controlled by several growth factors produced by both neurons and glial cells in a family of proteins
called ______
neurotrophins
The onset of regeneration is signaled by changes in the
perikaryon that characterize the process of _______
chromatolysis
Autonomic nerves use two neuron circuits. The first neuron of the chain, with the ____ is located
in the CNS
preganglionic fiber,
. Its axon forms a synapse with _______ of the second multipolar neuron in the chain located
in a peripheral ganglion system
postganglionic
fibers
As indicated earlier autonomic nerves make up the autonomic nervous system. This has two parts:
the sympathetic
and the parasympathetic divisions
