Histology of the Nervous System 2011

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Histology of the Nervous System

Cerebrum, Cerebellum and Spinal

cord

A/P Dr Nan Ommar

Department of Basic Medical Sciences

Faculty of Medicine and Health SciencesUNIMAS



Cells of the Nervous system

• Neurons = nerve cells

• Neuroglia = supporting cells

In CNS: OligodendrocytesAstrocyte

Microglia

Ependyma cells

In PNS:

Schwann cells

Satellite cells Astrocyte

Neuron

Ependyma

Oligodendrocyte

Microglia

Capillary



Neuroglia

• Ten times more numerous

than neurons• About ½ the total volume of

brain and spinal cord

•

Most common origin of cerebral tumours



Neuroglia in CNS

• Astrocytes-star shaped,

processes in contact with

blood vessel

– physical & metabolic support

– maintenance of the composition

of extracellular fluid – removal of transmitters from

synapses & metabolism of

transmitters



Neuroglia-CNS Cont;

• Oligodendrocytes-

– have fewer &shorter processes

– forms parts of myelin sheatharound several axons (50) in CNS-

– functional homologue of Schwanncells (PNS )

• Microcyte (microglia)-

– small cells ,complex shapes,

– only glial cell of mesodermal origin

– -phagocytic cells

Astrocyte



Neuroglia in CNS Cont;

• Ependymal cells

– simple epithelium that lines theventricles and central canal of spinal cord,

– cuboidal or low columnar in shape

– Do not rest on basementmembrane, ramifies with asrtocyteprocesses

– cilia &microvilli at luminal surface

– for propulsion, absorption,secretion



Neuroglia cells of ganglia

• Satellite cells/Capsulecells are foundsurrounding nerve cellsin the sympatheticganglion and dorsalroot ganglion of spinalcord

• They are the neurogliacells of the peripheralnervous system



Histology of neurons and neuroglia



Cerebrum

• The cerebral cortex is a

sheet of neural tissue

that is outermost to the

cerebrum

•

Consist of convolutedcortex of grey matter

overlying the central

white matter.

FrontalParietal

OccipitalTemporal

Cerebellum

http://www.answers.com/topic/cerebrum

http://www.answers.com/topic/cerebrum



Cerebral Cortex

• The human cerebral cortex is2 – 4 mm (0.08 – 0.16 inches)thick

•Gray matter is formed fromneurons and theirunmyelinated fibers,

• White matter below the the

gray matter is formedpredominantly by myelinatedaxons

http://www.answers.com/topic/neuron

http://www.answers.com/topic/myelin

http://www.answers.com/topic/axon-1

http://www.answers.com/topic/axon-1

http://www.answers.com/topic/myelin




Layers and classification of cerebral

cortex

• It is constituted of up to six horizontal layers, each of which has a different composition in terms of neuronsand connectivity.

• Based on the differences in lamination the cerebralcortex can be classified into two major groups:

• Isocortex (homotypical cortex), the part of the cortexwith six layers.

• Allocortex (heterotypical cortex) the part of the cortexwith less than six layers (varying in number).

• The allocortex includes the olfactory cortex and thehippocampus.


http://www.answers.com/topic/neocortex

http://www.answers.com/topic/allocortex

http://www.answers.com/topic/olfactory-system

http://www.answers.com/topic/hippocampus

http://www.answers.com/topic/hippocampus

http://www.answers.com/topic/olfactory-system

http://www.answers.com/topic/allocortex

http://www.answers.com/topic/neocortex




Histology of cerebrum• Neurones - 5

morphological types

- Pyramidal cells,

- Stellate (granule),

- cells of Martinotti,- fusiform cells and

- horizontal cells of

Cajal

• Neuroglia- astrocytes,

oligodendrocytes &

microglia



Layers and Columns

• Neurons in various layers connectvertically to form smallmicrocircuits, called columns.

• Different neocortical architectonicfields (Broadmann’s area) aredistinguished upon

– variations in the thickness of theselayers,

– their predominant cell type and

– other factors such as neurochemicalmarkers.

http://www.answers.com/topic/cortical-column

http://www.answers.com/topic/cortical-column



Layers of the cerebral cortex

• The outermost layer of theneocortex, layer I, consists of amesh of axons and dendrites withvery few cell bodies.

• The other layers consist of

pyramidal and non-pyramidalneurons in varying proportions.

• Layer IV contains a high proportionof non-pyramidal cells, andreceives most of the incomingfibres from the thalamus.

• Layers V and VI have particularlylarge pyramidal cells that projectto subcortical centres, such as thespinal cord and thalamus.



Layers of the Grey matter of Cerebral Cortex

I. Plexiform (molecular layer)

- mainly dendrites and axons andhorizontal cells of Cajal

II. outer granular layer

- Small pyramidal cells and stellate cells

III. Pyramidal cell layer- Pyramidal cells of moderate size

IV. Inner granular cell layer

- Stellate cells +++

V. Ganglionic layer

- Large pyramidal cells, stellate cellsand cells of martinotti

VI. Multiform layer

-all type of cells + fusiform cells

I

II

III

IV

V

VI

White matter



Cortical neurons-Pyramidal cells• A pyramidal cell has a the apical dendrite, which

sprouts out of the top of the cell body and

extends up toward the cortical surface.

• The other dendrites called basal dendrites, form

a skirt around the lower part of the cell body.

•

All dendrites bear large numbers of spines, onwhich incoming nerve fibres terminate to form

synapses.

• Pyramidal cells in layer V ganglionic layer- largest

size and called Betz cells (upper motor neurons).

•

From the motor cortex , the axons project all theway to the spinal cord to contact motor neurons,

which relay the signals out to the muscles.

• Most pyramidal neurons are excitatory and useglutamate as a neurotransmitter.



Pyramidal cells of the Cerebral Cortex

Silver stain

H&E stain



Cortical Neurons –Non-pyramidal cells• Non -pyramidal cells are called interneurons

because they have relatively short axons thatmake local connections and do not leave the

cortex itself.

• Inter-neurons are found throughout the cortex.

• Have a smaller cell body, smaller dendritic

arborization.• Non-pyramidal cells, receive axons from the

thalamus, from other cortical areas, and from

other local interneurons

• Non-pyramidal cells can be either excitatory or

inhibitory .

• If inhibitory they commonly use the important

inhibitory substance GABA (gamma-

aminobutyric acid ) as the transmitter at their

synapses.



Histology of Cerebellum

• Cortex forms deeply

convoluted folds called

folia.

• Has a central core of white

matter containing 4 pairs

of nuclei (Dentate,

Emboliform, Fastigius,Globose ). DEFG



Histology of Cerebellum

• Cerebellar cortex has auniform structure in allparts

• Consists of 3 layers

(I) Molecular layer mostsuperficial

(II) Purkinje cell layer

(III) Granular layer

I

II

III

M

G

P



Layers of the Cerebellar Cortex



Types of cells in Cerebellum

FIVE main types of

neurones:

- Granule cells

- Purkinje cells

- Stellate cells

- Basket cells

- Golgi cells




• I. Molecular layer

contains relatively

few neurons &

large number of

unmyelinated

fibers.




• 2.Purkinje cell layer contains a

single layer of large flasked-

shaped cells with extensively

branching dendrites in the

molecular layer and axon that

passes down to the granular cell

layer.

• 3.Inner granular cell has larger

number of granule cells.

• Their axons run directly upwards

to the molecular layer and

bifurcate in a " T " form.



Afferent & Efferent fibers

• Afferent fibers (excitatory)

(I) Mossy fibers from spinalcord synapse with granulecells.

(II) Climbing fibers mainlyfrom olivary nucleus of

medulla to molecular layerto synapse with purkinjedendrites.

• Efferent fibers (inhibitory)

Purkinje cell axons pass

down through the granularcell layer into the whitematter to the deepcerebellar nuclei.



Cross –section of the Spinal cord



Cross Section of Spinal Cord

• It has anterior median

fissure and posterior

median sulcus.

• In transverse section, it

shows the central H -

shaped grey matter

surrounded by thewhite matter.

Central canal lined by ependyma cells



Cross Section of Spinal Cord

• The H - shaped grey

matter has narrow

posterior horns andthicker anterior horns

and are connected by

horizontal bar or grey

commisure.



Anterior Horn Cells of Spinal cord

• Anterior horn cells are

multipolar neurons.• They are called lower

motor neurons

• dendrites pass to the

lateral white column

• axon pass out into the

white matter and proceed

to the surface of the spinal

cord in groups and form

the anterior/ventral nerve

root…… skeletal muscles



Cross Section of Spinal Cord at different levels

•The dorsal and ventral horns

are larger and wider at levels of

the cervical and lumbosacral

enlargements.

•The lateral horn is present

from L1 to T2.•The white matter increases in

absolute amount from caudal

to rostral.

Histology of the Nervous System 2011

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