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

Nervous Tissue  One of the four basic tissues  Generates, conducts & transmits impulses  In 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 body  Abundant RER called Nissl bodies in cell body & dendrites but absent in axon  Large nucleus with euchromatin & prominent nucleolus  Neurons 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 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 axons  Each bundle contains myelinated & umyleinated axons  Contains motor & sensory axons  Mo 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 groups  Each neuron is surrounded by a capsule of supporting cells called satellite cells  Contains myelinated axons  Sensory ganglion

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