Download Histology of Brain Stem, Cerebrum and Cerebellum

Histology of Brain Stem, Cerebrum and
Cerebellum
Brain stem
• Brain stem is structurally continuous with the spinal cord.
• It consists of;
– medulla oblangata
– pons
– mesencephalon
• The regions of gray and white matter are not clearly separated
• The nuclei of the cranial nerves appear as islands surrounded by
white matter
Meninges
• Connective tissue coverings of the brain and spinal cord
Dura Mater
• Dense, collagenous connective tissue
• Dura of the brain is composed of two layers;
– periosteal dura mater (outer);
• attached to the inner surface of the skull
• serves as the periosteum
• osteoprogenitor cells, fibroblasts, collagen bundles, blood vessels
– meningeal dura mater (inner);
• fibroblasts, fine collagen fibers, small blood vessels
• Dura of the spinal cord
– forms a continuous tube around the spinal cord
– does not adhere to the walls of the vertebral canal
– pierced by the spinal nerves
– epidural space;
• between the dura mater and the periosteum of the vertebral canal
• filled with epidural fat and a venous plexus.
Arachnoid Mater
• Connective tissue without blood vessels,
blood vessels course through it
• Composed of two regions:
1)
2)
sheet-like membrane in contact with dura
arachnoid trabeculae
 loosely arranged cells (modified fibroblasts)
with collagen fibers
 contact the underlying pia
• Subarachnoid space;
– cavities between the trabeculae
– filled with cerebrospinal fluid (CSF)
• Arachnoid villi;
– regions where arachnoid perforates the dura
for the passage of CSF into the dural venous
sinuses
• Clinical significance: Subdural space is a “potential space”, it appears
only after subdural hemorrhage, when blood forces two layers apart
Pia Mater
• Innermost layer of the meninges
• Follows all the surface irregularities of
CNS
• Composed of a thin layer of flattened,
modified fibroblasts and abundant
blood vessels surrounded by fine
connective tissue fibers
• Completely separated from the
underlying neural tissue by basement
membrane and neuroglial processes
Cerebrospinal Fluid
• Bathes, nourishes and protects the brain and spinal cord
• Produced by the choroid plexus
• %90 water, low protein and low density, rich in ions, few
desquamated cells, 2-5 lymphocytes/ ml
• Reabsorbed through the thin cells of the arachnoid villi
into the superior sagittal venous sinus
• Clinical correlations;
– Hydrochephalus; reason is a decrease in absorption of the
fluid or a blockage within the ventricles which increases
intracranial pressure.
– Congenital hydrocephalus; leads to enlargement of the
head, followed by impairment of mental and muscular
functions and death if left untreated.
Choroid Plexus
• Fenestrated capillaries covered by the modified ependymal cells
• Modified ependymal cells
–
–
–
–
tight junction
infolding of the basal plasma membrane,
microvilli
mitochondrion
• Extend into the ventricles of the brain
• Produces CSF
Ventricles
•
•
•
•
Cavities in the brain (4th, 3rd, lateral)
Contain CSF
Ependymal cells
Tanycytes;
– special ependymal cells located in the floor of the 3rd ventricle.
– processes extend deep into the hypothalamus.
– Transfer chemical signals from CSF to CNS.
Cerebrum
• Cortex
– gray matter (peripheral)
• Medulla
– white matter
Layers of the Cerebral Cortex
I.
Molecular layer; parallel nerve fibers, horizontal
cells of Cajal, neuroglia
II. External granular layer; small pyramidal cells,
granule (stellate) cells, neuroglia
III. External pyramidal layer; large pyramidal cells,
neuroglia
IV. Internal granular layer; thin layer composed of
closely arranged small granule (stellate) cells,
neuroglia.
V. Internal pyramidal layer; largest pyramidal cells
(Betz cells), neuroglia. This layer has the lowest
cell density of the cerebral cortex
VI. Multiform layer; cells of various shapes
(Martinotti cells, fusiform cells, pyramidal etc.),
neuroglia
• Isocortex (neocortex) is the outer layer of the cerebral hemispheres made
up of typical six layers
• Anisocortex (archicortex) (e.g. hippocampus)
Hippocampus (sea horse)
• hippocampus, dentate gyrus, temporal lobe gyrus
• polymorphic layer; nerve fibers, small cell bodies of interneurons
• pyramidal cell layer; pyramidal cells
• molecular layer; dendrites of the pyramidal cells
Dentate gyrus
• polymorphic layer; nerve fibers, interneurons
• granule cell layer; granule cells
• molecular layer; dendrites of the granule cells
Hilus
• region where the head of hippocampus join the dentate gyrus
• contains multipolar neurons
Cerebellum
• Outer gray matter “cortex”
– Molecular layer- Purkinje cell layer
– Granular layer
• Inner white matter “medulla”
• Surrounded by piamater
Molecular layer
• lies directly below the pia mater
• contains
–
–
–
–
superficially located stellate cells
basket cells
Purkinje cells and their dendrites
unmyelinated axons from the granular layer (parallel fibers)
• Purkinje cells
–
–
–
–
large pear-shaped cells
arborized dendrites projecting into the molecular layer
myelinated axons project into the white matter
only cell of the cerebellar cortex that sends information
(always inhibitory) to the outside
• Contains
Granular layer
– small granule cells
– Golgi type II cells
– glomeruli; synaptic regions between axons entering the cerebellum and the
granule cells.
• Axons of the granule cells extend to the molecular layer and synapse with
the dendrites of Purkinje cells and basket cells (parallel fibers).
• Parallel fibers extend parallel to the longitudinal axis of the folium in the
molecular layer.
Barriers in the CNS
• Glia limitans externa- interna
• Blood- brain barrier
• Blood- CSF barrier
Blood-Brain Barrier
1) endothelial cells lining the continuous capillaries linked by tight junctions
2) basal lamina
3) end-feet of astrocytes
• This barrier prevents the free passage of selective blood-borne
substances into the neural tissue.
• O2, CO2, water, small lipid soluble materials can penetrate the barrier.
• Transfer of glucose, amino acids, vitamins, nucleosides and ions require
transmembrane proteins.
References
1.
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5.
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Histology and Cell Biology: An Introduction to Pathology by Abraham L
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