Histology of

Central Nervous System

Dr..Deepak N.Khedekar.Asst. professor

Dept of AnatomyLTMMC & GH,MUMBAI

2014

Histology of CNSThere are only two functional cell types

1.neurons - excitable nerve cells that transmit electrical signalsMost neuron cell bodies are located within the CNS

Nuclei: clusters of neuron cell bodies in the CNS

Ganglia: clusters of neuron cell bodies in the Peripheral Nervous System.

2.neuroglia (glial) cells - supporting cells

Neurons…

Motor neuron

NUN

D

DA

AH

NB

NB

D

V

A-axon D-dendrite N-nucleus NB-Nissl bodyAH-axon hillock V-blood vessel NU-nucleolus

Basic types of neuronal structure

Neuroglia-Supporting cells…

Neuroglia - 4 types in the CNS

Astrocytes

• star shaped with many processes,connect to neurons; help anchor them to nearby blood capillaries

• control the chemical environment of the neurons

Microglia

• oval with thorny projections

• monitor the health of neurons, if infection occurs, they change into macrophages

Neuroglia…

Neuroglia …Ependymal cells :

• shape from squamous to columnar; are ciliated

• line the cavities of the brain and spinal cord

• form a barrier between the neurons and the rest of the body

Oligodendrocytes :

• have few processes

• line up along neurons and wrap themselves around axons

• form the myelin sheath

Neuroglia…

Neuroglia in the Peripheral NS

Satellite cells

• surround neuron cell bodies in the periphery

• maintain the extracellular environment

Neurolemmocytes (Schwann cells)

• surround axons/dendrites and form the myelin sheath around larger nerve fibers

• similar to oligodendrocytes in function –insulators

Slide 1.Spinal cord…

Spinal cord…

Spinal cord-Gray matter…

Multipolar neurons:

• Vesicular nucleus with distinct nucleolus

• Nissl subastance (basophilic)

Neuroglia :small light staining supportive cells

small basophilic nuclei

Spinal cord…

Spinal cord- Gray mater…

Spinal cord- White matter

Closely packed groups of myelinated axons

Myelin sheaths appear as clear spaces around dark staining axons

Anterior horn of spinal cord

Slide 2.Cerebral Cortex

• The grey matter consists of neuron cell bodies and their dendritic interconnections & glialcells. The cortex contains 30 billion neurons.

• The evolved cortex in mammals called neocortex consists of 6 layers of neurons.

Cerebral Cortex…Neocortex

• >90 % of our total cortical area.

• 6 layered structured, Refered to as homogenic cortex.

Paleocortex

• Covers some parts of the base of the telencephalon.(olfactory area)

-Forms heterogenic cortex.

Archicortex

• The hippocampal formation.

Neuron Cell types

• Two principal cell types are present in neo cortex. (PSM FuC)

– 1.Pyramidal cell .

– 2.Stellate cell .

• Other cells are …

– 3. Cells of Martinotti

– 4.Fusiform cells

– 5.Horizontal cells of Cajal

.

.

Pyramidal Cells…

• Pyramid shaped 10 micr. to 70 micr.).

• Axon arises from the base and the dendrite from the apex.

• The largest of the pyramidal cells are called the BETZ cells.

Functions of pyramidal cells…

• The apical dendrites of pyramidal cells are studded with dendritic spines.( preferential site of synaptic contact)

• Most or all pyramidal cells have long axons

that leave the cortex to reach either other cortical areas or to various subcortical sites.

• Pyramidal cells are the principal output neurons.

Stellate Cells…

Also known as granular cells.

-They are the principal interneurons of cortex .

--They are typically small (< 10 micrometres) multipolarneurons.

• principal interneurons

Cells Of Martinotti…

• Small polygonal cells.

• Forms synapses with the pyramidal cells.

• Have very few short dendrites.

• axon extends towards the surface and bifurcate to run horizontally in most superficial layers.

Fusiform Cells…

• Spindle shaped cells, are oriented at right angles to the cortex.

• Axon arises from the side of the cell body and passes superficially.

• Dendrites extend from each end of the cell body branching into deeper and more superficial layers.

• Functions are similar to that of pyramidal cells.

Horizontal Cells Of Cajal (Or) RetziusCajal Cells…

• Small ,spindle shaped, oriented parallel to the surface.

• Least common cell type, found only in most superficial layer.

• Axons pass laterally to synapse with dendrites of pyramidal cells.

• prominent during development, but disappear after birth.

6 Layers Of Neocortex (MGP-PGM)

1.Plexiform or molecular layer 2.outer granular layer3.outer pyramidal cell layer4.inner granular layer 5.inner pyramidal cell layer/ganglion cell layer6.multiform cell layer

Layers are not equally prominent everywhere. They form granular & agranular layers.

6 cortical layers …

1.Plexiform layer or molecular layer

• Most superficial layer,

• contains many dendritic and axonal synapses with one another.

• Sparse nuclei of neuroglia are seen

• Occasional horizontal cells of cajal are seen.

• 2.OUTER GRANULAR LAYER

• Dense population of small pyramidal cells and stellate cells.

• Different types of neuroglial cells

3.Pyramidal cell layer

• Moderate sized pyramidal cells predominate.

• Large pyramidal cells are present in further deeper layers.Martinotti cells are also present.

• 4.INNER GRANULAR LAYER

• Consists of densely packed granule cells /stellatecells

5.GANGLIONIC LAYER

• Large pyramidal cells,Stellate cells (few),Cells of martinotti

• Huge pyramidal Betz cells of motor cortex are present. Hence the name ganglion cell layer.

Slide 3.Cerebellum…

Gray matter (Cerebellar cortex) consist of 3 layers

Outer molecular layer

middle purkinje layer

Inner granular layer

White matter consist of myelinated nerve fibers or axons

Cerebellum Gray matter(10x)…

Cerebellum(40x)…

Cerebellum…

Outer molecular layer

• Few, small neurons (basket cells and stellate cells)

• Many fibers extending parallel to length of folium

middle purkinje layer

• Purkinje cells few in no., pyriform in shape, dendrites in molecular layer

Inner granular layer

• Numerous neurons with prominent nuclei

• Glomeruli-empty spaces in granular layer

Cerebellum(40x)…

Slide 4.Sensory Ganglia…

• Two types: spinal (dorsal root) and cranial ganglia associated with spinal and cranial nerves, respectively

• Contain large sensory neurons and abundant small glial cells, called satellite cells

• Sensory neurons are pseudounipolar

Sensory or Dorsal root ganglia(10x)

Dorsal root ganglia…

• Enclosed in irregular CT containing adipose tissue,nerves,blood vessels.

• Consist of unipolar neurons with eosinophilic cytoplasm and centrally placed round nucleus, darkly stained nucleolus

• Cells surrounded by well defined connective tissue capsule containing numerous satellite cells (neuroectodermal origin)

Sensory or dorsal root ganglion…

Sensory or Dorsal root ganglia…

Sensory or Dorsal root ganglion…

Autonomic-Sympathetic ganglia…

Autonomic-Sympathetic ganglia…

• Enclosed in irregular CT containing adipose tissue,nerves,blood vessels.

• Consist of multipolar neurons with eosinophilic cytoplasm and ecccentrallyplaced round nucleus, darkly stained nucleolus

• Cells surrounded by ill defined connective tissue capsule containing few satellite cells(neuroectodermal origin)

Sensory Ganglia vs ANS Ganglia

At the end of the every lecture…..