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. Nervous Tissue
Originally Written By: Dr. Mohammad Al-Attayeb
Typed in the Computer By: Abo Malik
Thanks 4: Dr.I

2. Nervous Tissue
One of the four basic tissues
Generates, conducts & transmits impulses
In CNS (brain & spinal cord)
In PNS (nerves & ganglia

3. Components of Nervous Tissue
Neurons (Nerve cells)
Neuroglia (Supporting cells)

4. Neuron (Nerve Cell)
 Consists of:-
1. Cell body (Perikaryon)
2. Cytoplasmic processes:-
– Dendrites
– Axon

5. The Neuron Cell Body
Large basophilic cell body
Abundant RER called Nissl bodies in cell
body & dendrites but absent in axon
Large nucleus with euchromatin &
prominent nucleolus
Neurons do not divide

8. 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)

10. 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

11. 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

12. 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

13. 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

16. CELL BODY
Muscle Fiber

17. 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

19. Structure of Peripheral Nerve
Contains parallel bundles of axons
Each bundle contains myelinated &
umyleinated axons
Contains motor & sensory axons
Mo nerve cell bodies

20. 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

24. 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)

26. 1. Dorsal Root Ganglion
(Spinal Ganglion)
Contains pseudounipolar neurons in groups
Each neuron is surrounded by a capsule of
supporting cells called satellite cells
Contains myelinated axons
Sensory ganglion

28. Sympathetic Ganglion
Contains multipolar neurons separated by
spaces containing unmyelinated axons
Capsule of satellite cells is not prominent
It is a motor ganglion
Contains synapses