Download Nervous Tissue

NERVOUS TISSUE
Dr.Mohammed Shamiah
Nervous Tissue
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1- Central Nervous System (CNS),
consists of the brain and spinal cord.
2- Peripheral Nervous System (PNS),
consists of cranial nerve, spinal nerves, ganglia,
nerve endings and glial cells.
Dr.Mohammed Shamiah
The Neuron
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It is the structural and functional unit of nervous
system.
It is formed of a nerve cell & its processes (axon &
dendrites).
Dr.Mohammed Shamiah
The nerve cells:
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Size:
Range from 4-100 microns.
Small cells as in cerebellum.
Large cells as in cerebrum.
Dr.Mohammed Shamiah
Structure of nerve cells:
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The cell membrane are very thin.
 The Nucleus has a thick nuclear membrane and
clear nucleolus.
 The cytoplasm contains all cell organoids &
inclusions but with no centrioles.
 The cytoplasm is rich in microtubules &
nerofilaments.
 The cytoplasm is rich in Nissl granules or bodies.
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Dr.Mohammed Shamiah
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Nissl granules are specific basophilic bodies
consisting of rough endoplasmic reticulum with their
attached ribosomes.
Nissl granules are not present in axon and near
the nuclear or cell membrane.
Nissl granules help in nutrition & carrying the
memory of nerve cells.
Dr.Mohammed Shamiah
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Mitochondria are present in the body & processes
of nerve cell.
Cell inclusion of the nerve cells:
Glycogen granules are important for the function of the
nerve cell.
Melanin pigments may be present in some nerve cells.
Yellowish lipofuscin granules are present & increase in old
age.
Dr.Mohammed Shamiah
Classification of Neurons
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According to the shape of nerve cells:
I.
1)
2)
3)
4)
Unipolar neurons : amacrine cells of the retina.
Pseudo-unipolar neurons: spinal ganglia.
Bipolar neurons: retina & olfactory mucosa .
Multipolar nerve cells: (stellate, pyramidal & pyriform-shaped )
According to the functions:
II.
1)
2)
3)
Sensory neurons.
Motor neurons.
Interneurons.
According to the length of the axons:
III.
1)
2)
Golgi Type 1 neurons. (long axons as the neurones of cerebral cortex)
Golgi Type 2 neurons. (short axons as neurones of retina)
Dr.Mohammed Shamiah
NEURON TYPES
Bipolar Neuron
(retina & olfactory epithelium)
Pseudounipolar Neuron
(sensory spinal reflex arc)
Unipolar Neuron
(embryonic)
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Dr.Mohammed Shamiah
Dr.Mohammed Shamiah
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Nerve cell processes
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The Axon:
- Formed of cytoplasm known as axoplasm containing
mitochondria, neurofibrils & neurotubule.
- Surrounded by membrane called (axolemma).
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The Dendrites:
They are extensions of the cell body.
They conduct nerve impulses towards the cell body.
Dr.Mohammed Shamiah
Differences Between Axon and Dendrites
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The Axon
The Dendrites
1. Single process.
2. Thin & long.
3. Uniform diameter along its
length.
4. Branches & also give collateral.
1. Usually multiple process.
2. Usually short & thick.
3. Their thickness decreases
gradually towards its end.
4. Have many fine side projections
called spines.
5. Contains neurofibrils but no Nissl 5. Contain Nissl granules &
granules.
neurofibrils.
6. Two types of axonal transport
6. Receive impulses from other
neurons .
exist (Antigrade & retrograde).
Dr.Mohammed Shamiah
Types of nerve axons according to
covering sheath:
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1- Naked nerve axons without a myelin sheath
&without a neurolemma.
(e.g. grey matter)
2- Covered with myelin sheath but without
neurolemma.
(e.g. white matter)
3- Nerve fibres covered with myelin sheath & covered
also with neurolemma.
(e.g. peripheral somatic axon outside the spinal cord).
4- Covered with neurolemma but are not covered with
myelin sheath.
(e.g. post ganglionic sympathetic
nerve axon).
Dr.Mohammed
Shamiah
The Myelin Sheaths
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It is a fatty tubular covering around the axon.
Formed by neurolemma cells surround the peripheral
nerves.
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In the brain formed by neurglia cells(oligodendroglia).
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Composed of cholesterol, fatty acids &phospholipids.
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The Myelin Sheaths is white in color.
Dr.Mohammed Shamiah
١٥
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Interrupted at intervals by nodes of Renvier &
Lantermann’s clefts.
At the nodes of Renvier, the axon not covered by
myelin sheath.
Lantermann’s clefts: discontinuities in the myelin
sheath, facilitate the passage of the nutrition from
Schwann cells to the myelin sheath.
Dr.Mohammed Shamiah
Function of Myelin sheath:
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1)
2)
3)
Protection of the axons.
Isolates nerve impulses.
Accelerate conduction of nerve impulse.
Dr.Mohammed Shamiah
Schwann cells (neurolemmal)
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Formed of chain of Schwann cells around Myelin
Sheath.
Each cell corresponds to an internodal segment & its
comes in contact with axon at the nodes of Ranvier.
Function of neurolemmal cells:
1- Isolate nerve impulses.
2- Help in regeneration of neurons.
3- Form the myelin sheath around axons.
Dr.Mohammed Shamiah
Dr.Mohammed Shamiah
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Dr.Mohammed Shamiah
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Dr.Mohammed Shamiah
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ANATOMY OF A NEURON
axons
impulse conduction
dendrites
axo-somatic synapse
axo-dendritic synapse
boutons
Nissl’s
substance
axon
hillock
oligodendrocyte
axon
myelin sheath
myelin sheath
myelin sheath
axo-axonic synapse
unmyelinated collateral
central nervous system (CNS)
peripheral nervous systen (PNS)
Schwann cell
motor end plate
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synaptic vesicles
motor
end
Dr.Mohammed
Shamiah
plate
MOTOR NEURON CELL BODY (H&E)
DENDRITIC SPINES (boutons)-silver
axo-denritic
synapses
dendrite
(boutons)
Nissl’s
substance
nucleolus
dendrite
nucleus
axon
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Dr.Mohammed Shamiah
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Thank you
Dr.Mohammed Shamiah