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