Histology of the Nervous System

Divisions of the Nervous SystemAnatomically

CNS: Brain and Spinal cord

PNS : Nerves and Ganglia

Histologically

Nerve cells

Glial cells

Neurons

Are the unit structure and function Function: Reception, Processing and

Transmission of nerve stimuli

Triggering certain cell activity

Release of neurotransmitters

Parts: Cell body

Dendrites

Axon- Aroriziation, Bouton

They vary in shape

They vary in size (5-150 µm)

Neurons can be classified

Morphologically:

Multipolar

Bipolar

Pseudounipolar

Functionally:

Motor

Sensory

Interneurons

Neuron consists of:Cell body: the trophic center

Dendrites: Receive and process of signals

Many arborizations

Dendritic spines

Axon: Structure

Anterograde flow-

Slow for proteins and actin,tubulin

Medium for mitochondria

Fast for neurotransmitters,AA, vesicles

Retrograde flow

Motor proteins- Kinesin and dyenin

SynapsesStructure

Types:

Chemical and Electrical

Excitatory and Inhibitory

Symmetrical and asymmetrical

Glial Cells

1. Oligodendrocytes

2. Schwann cells

3. Astrocytes

4. Ependymal cells

5. Microglia

Nerves

Consists of nerve fibers

Endoneurium

Perineurium

Epineurium

Nerve fibers

Myelinated, Node of Ranvier

Unmyelinated

Ganglia• Structure:

Cells, axons, Satellite cells

• Types:Sensory

Autonomic

Regeneration and Degeneration

• Destroyed processes and nerve fibers can regenerate to certain extent?

• Dead neuron will not affect neuron in vicinity except if one neuron is in contact with dead one

(Transneuronal degeneration)

Axon Transection1. Proximal segment

regenerate while the

distal one degenerate

2. Perikaryon undergoes

chromatolysis

3. Proximal segment first

degenerate then start

regeneration

4. Distally, axon and myelin

sheath degenerate and

removed except the surroundings

Axon Transection

5. Schwann cells proliferate

giving solid cellular columns

which direct the sprouting

nerve

6. Proximal end grows and

branches giving many filaments

which progress in the direction

of Schwann cell columns

7. Neuroma: is a mass of growing

nerve tissue fail to meet the

distal segment

Clinical Application

1. Multiple Sclerosis

2. Nerve Tissue Tumors

Medulloblastoma

Glioma (Astrocytoma)

Schwannoma