Nervous Tissue
Originally Written By: Dr. Mohammad Al-AttayebTyped in the Computer By: Abo MalikThanks 4: Dr.I
Nervous Tissue
One of the four basic tissuesGenerates, conducts & transmits impulsesIn CNS (brain & spinal cord)In PNS (nerves & ganglia
Components of Nervous Tissue
Neurons (Nerve cells)Neuroglia (Supporting cells)
Neuron (Nerve Cell)
Consists of:-1. Cell body (Perikaryon)
2. Cytoplasmic processes:-– Dendrites
– Axon
The Neuron Cell Body
Large basophilic cell bodyAbundant RER called Nissl bodies in cell
body & dendrites but absent in axonLarge nucleus with euchromatin &
prominent nucleolusNeurons do not divide
Types of Neurons
According to the number of processes arising from the cell body:-
1. Bipolar:-
Two processes (olfactory epithelium)
2. Multipolar:-
More than two processes (e.g. sympathetic ganglia)
3. Pseudounipolar:-
One process dividing into two (e.g. spinal ganglia)
Types of Axons
1. Myelinated axon (with myelin sheath) may be sensory or motor
2. Unmyelinated axon (without myelin sheath) may be sensory or motor
All types of axons in PNS are supported by cells called Schwann cells
Schwann Cells
The Schwann cells of myelinated axon in PNS form myelin sheath around the axon
In the unmyelinated axon a Schwann cell supports several axons without forming myelin sheath
Schwann cells have a basal lamina
1. Myelinated Axon
1. Each Schwann cell forms one segment of myelin sheath around the axon called internode
2. Each internode is about 200-1000 μm long
3. Between internodes is a gap called node of Ranvier where there is no myelin sheath
What Is Myelin Sheath
Myelin sheath is concentric layers of the Schwann cell membrane around the axon
It contains the lipids & proteins of the cell membrane of the Schwann cell
CELL BODY
Muscle Fiber
2. Umyelinated Axons
Successive Schwann cells surround the axon without forming myelin sheath
Many axons are found in deep grooves on the surface of a single Schwann cell
They are smaller than myelinated axons
Structure of Peripheral Nerve
Contains parallel bundles of axonsEach bundle contains myelinated &
umyleinated axonsContains motor & sensory axonsMo nerve cell bodies
Connective Tissue of the Nerve
Epineurium:- external layer of dense irregular CT covering the nerve
Perineurium:- layers of flat cells with tight junctions & basal lamina around each bundle of axons
Endoneurium:- innermost layer of reticular CT around each Schwann cell covering the axon
Ganglia
Ganglia are groups of neuron cell bodies outside the CNS
Types of ganglia:-1. Dorsal root (spinal) ganglia
2. Autonomic ganglia (e.g. Sympathetic ganglia)
1. Dorsal Root Ganglion(Spinal Ganglion)
Contains pseudounipolar neurons in groupsEach neuron is surrounded by a capsule of
supporting cells called satellite cellsContains myelinated axonsSensory ganglion
Sympathetic Ganglion
Contains multipolar neurons separated by spaces containing unmyelinated axons
Capsule of satellite cells is not prominentIt is a motor ganglionContains synapses