Central Nervous System. Major Anatomic regions of Brain Cerebrum Diencephalon Brainstem Cerebellum.
Histology of Brain Stem, Cerebrum and Cerebellum
Transcript of 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) sheet-like membrane in contact with dura 2) 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
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
Layers of the Cerebral Cortex
• 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
• 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
Molecular layer
• Contains – 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.
Granular layer
Barriers in the CNS
• Glia limitans externa- interna
• Blood- brain barrier
• Blood- CSF barrier
Blood-Brain Barrier
• 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.
1) endothelial cells lining the continuous capillaries linked by tight junctions 2) basal lamina 3) end-feet of astrocytes
References
1. Histology: A Text and Atlas by Michael H. Ross, Wojciech Pawlina (2010). 6th ed. Lippincott Williams & Wilkins, Philadelphia. ISBN: 978-0-7817-7200-6
2. Basic Histology: Text & Atlas by Luiz Junqueira, Jose Carneiro (2005). 11th ed. McGraw-Hill, New York. ISBN: 0-07-111888-8
3. Color Textbook of Histology by Leslie P. Gartner, James L. Hiatt (2001). 2nd ed. W.B. Saunders Company, Philadelphia. ISBN: 0-7216-8806-3
4. Histology and Cell Biology: An Introduction to Pathology by Abraham L Kierszenbaum, Laura Tres (2011). 3rd ed. Elsevier Saunders, Philadelphia. ISBN: 978-0-323-07842-9
5. Netter’s Essential Histology by William K. Ovalle, Patrick C. Nahirney (2007). 1st ed. Elsevier Saunders, Philadelphia. ISBN: 978-1-929007-86-8