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HISTOLOGY OF NERVOUS TISSUE
BY
DR. MUDASSAR ALI ROOMI
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Overview-Nervous system
Anatomically, nervoussystem is divided intoCNS & PNS.
CNS includes brain andspinal cord.
PNS includes nervesoutside of CNS and their
associated ganglia(small groups of nervecell bodies outside theCNS).
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ANATOMIC AND FUNCTIONAL DIVISIONS OF
NERVOUS SYSTEM
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Cells of nervous tissue
TWO TYPES OF CELLS ARE
PRESENT IN THE NERVOUS
TISSUE:
Nerve cells or Neurons:
which are excitable and
conduct electrical
impulses
Glial (neuroglial) cells or
supporting cells: which
support, nurture, and
protect the neurons.
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The Neuron
A neuron consists of:
a) Cell body
b) Processes (dendrites
and axons)
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Nerve cell body (perikaryon or soma)
It contains nucleus,cytoplasmic organelles,inclusions and cytoskeletalcomponents.
Nucleus: it is large sphericaland pale staining (vesicular)and centrally placed in mostof the cases. It contains
abundant euchromatin(chromatin is finelydispersed) and a largenucleolus (owl-eye nucleus).
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Nerve cell body (perikaryon or soma)
(a) Nissl bodies/granules/substance(chromatophilic substance) - basophilic
patches, cytoplasmic structures are
concentrations of RER. ***
The amount of chromatophilic substance
varies according to the type and
functional state of the neuron and isparticularly abundant in large nerve cells
such as motor neurons
(b) Neurofilaments - a variety of
intermediate filament - are aggregated
into neurofibrils visible in the cytoplasm
after silver impregnations.
(c) Surrounding the nucleus are elements
of the Golgi apparatus, mitochondria,
lysosomes, and microtubules.
(d) Pigment is sometimes present, e.g.,
melanin in substantia nigra neurons
(midbrain), and brown granules of
lipofuscin pigment (wear and tearpigment) in old neurons. ***28 May 2012 7
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dendrites
(a) Definition: These are theneuronal processes that receiveinformation and transmit it tothe cell body.
(b) Contain mitochondria,
microtubules, and granular ER.(c) Nissl granules are present in the
proximal part of the dendrites.
(d) Lack Golgi apparatus***
(e) dendrites have spine-like sideprocesses.
function: Dendrites integrate theexcitatory influences and increasethe receptive area of a neuron.
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axon
(a) Contains axoplasm flowingcentrifugally from the pyramidal shape
starting-point of the axon - the axon
hillock. ***
initial segment is the site b/w the apex of
the axon hillock and the start of the
myelin sheath. Action potential is
generated here.***
(b) Has mitochondria, neurofilaments,
microtubules, travelling vesicles, and, in
some neurons, secretion droplets, in the
axoplasm.
(c) Membrane of the axon is called as
axolemma, swelling out into a bag at itsends (synaptic boutons) which holds
vesicles.
Axonal transport: Kinesin, are
responsible for anterograde transport.
Dynein allows retrograde transport .***
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CLASSIFICATION OF NEURONS
Neurotransmitter Released
Cholinergic GABAergic
Cell Processes
MultipolarMotor, pyramidal, purkinje
BipolarSensory, retina, olfactory mucosa,
cochlear, vest. ganglia
Unipolar
rods & cones
Pseudo-unipolarSensory, dorsal roots & cranial
ganglia
Cell Size
Golgi I
Motor paramidal cell,
Golgi IIInterneuron spinal cord
Function
Motor Interneurons Sensory
Sympathatic Parasympathatic
Adrenergic Noradrenergic
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Morphological Classification of neurons-according to the number of cell processes
Unipolar neurons : rare in humans.
Found in the mesencephalic nucleus of
the 5th cranial nerve. probably occur only
during development.
pseudounipolar neurons, which have a
single process that bifurcates close to the
perikaryon, with the longer branchextending to a peripheral ending and the
other toward the CNS. Examples: found
in the dorsal root ganglia of spinal nerves,
and sensory ganglia of cranial nerves. **
Bipolar neurons, with one dendrite and
one axon. These neurons are found in
cochlear and vestibular ganglia, retina and
olfactory epithelium.
Multipolar neurons, which have one axon
and two or many dendrites. Most human
neurons are of this type. Some examples
are: pyramidal cells of cerebral cortex,
Purkinje cells of cerebellar cortex, andanterior horn cells of the spinal cord.
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Classification of Neurons by
Functional Role
Motor neurons
Motor neurons control effector organs and
muscle fibers.
Sensory neurons
Sensory neurons receive sensory stimuli from
the internal or external environment and relay
them to the CNS.
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Classification of Neurons-according to
the length of their axonsGolgi type I neurons: possess many dendrites and a very long
axon that leaves the grey matter in which its cell body ispresent.
Examples:
pyramidal cells of the cerebral cortex anterior horn cells of the spinal cord.
Golgi type II neurons: possess many dendrites and a relativelyshort axon that does not leave the part of grey matter in
which the cell body of the neuron is present.Example:
Interneurons.
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