1st Lecture on Histology of Nervous Tissue by Dr. Roomi

7/31/2019 1st Lecture on Histology of Nervous Tissue by Dr. Roomi

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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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1st Lecture on Histology of Nervous Tissue by Dr. Roomi

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