Post on 15-Jul-2020
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Histology of the CNS
Lecture Objectives• Describe the histology of the cerebral cortex layers.
• Describe the histological features of the cerebellum; layers and cells of cerebellar cortex.
• Describe the elements of the blood‐brain barrier and the blood‐CSF barrier.
• Describe the structure of the choroid plexus and the meninges.
The central nervous system• Major parts
– Cerebrum• Cerebral cortex• Basal ganglia
– Diencephalon • Thalamus• Hypothalamus• Epithalamus
– Brainstem• Medulla• Pons• Midbrain
– Cerebellum– Spinal cord
The central nervous system
• Cerebrum, Cerebellum & Spinal cord• Almost no connective tissue therefore a relatively soft, gel‐like organs
Cerebral Cortex
• Cerebral cortex is gray matter overlying white matter–2‐4 mm thick containing billionsof cells
• Has six layers of cells with different forms and sizes
Cerebral Cortex• Neuronal cells in cortex
– Pyramidal cells• Efferent fibers• Small – more superficial • Large – Betz cells (motor cells)
– Stellate (granule) cells• Star shape• Connect to near neurons
– Cells of Martinotti• Axons to superficial layers
– Fusiform cells• Spindle shape• Vertical orientation• In deep layers
– Horizontal cells of Cajal• Spindle shape• Horizontal orientation• In superficial layers• Connect pyramidal cells
Cerebral Cortex• Layers of cerebral cortex
– Molecular layer• Area of connection between
different cells– Outer granular layer
• Small pyramidal & stellate cells– Pyramidal cell layer
• Medium size pyramidal cells & martinotti cells
– Inner granular layer• Stellate cells
– Ganglionic layer• Large pyramidal cells
– Multiform cell layer• Mix of different cells
Cerebral Cortex
– I – Molecular layer– II – Outer granular layer– III – Pyramidal cell layer– IV – Inner granular layer– V – Ganglionic layer– VI – Multiform cell layer
Cerebral Cortex: Pyramidal cells
Cerebellum
• Content– Cerebellar cortex (folia) & central nuclei are grey matter– Arbor vitae = tree of life = white matter
Cerebellum
• Cerebellar cortex• White mater (medulla)
Cerebellar cortex
• Three layers– Outer molecular layer– Central layer of large Purkinje
cells – Inner granule layer
Cerebellar cortex• Has three layers
– Outer molecular layer• Few neurons• Mostly unmyelinated fibers
– Central layer of large Purkinje cells • One layer of large cells
– Inner granule layer• Very small neurons (smallest in the
body) that is compactly disposed– Connect with the afferent fibers
Purkinje Cells• Purkinje cells has highly developed dendrites – Dendrites occupy most of
the molecular layer– Axons traverse the granular
layer to the central nuclei of the cerebellum
Spinal Cord
• Anterior median fissure• Posterior median sulcus• Gray and white commissures• Central canal• Anterior, posterior & lateral gray horns
– Anterior horns contain motor neurons– Posterior horns receive sensory fibers from neurons in the spinal ganglia
• Anterior, posterior & lateral white columns
Internal Anatomy of Spinal Cord
Spinal Cord
Spinal Cord
Gray matter of spinal cord
Central Canal
Spinal Cord• Gray mater
– Substantia gelatinosa (entire SC)
– Nucleus proprius (entire SC)– Nucleus dorsalis (C8‐L2)– Intermediolateral cell column
(T1‐L2, S2‐S4)– Medial motor nucleus (entire
SC)– Lateral motor nucleus
(enlargements)• White mater
– Fasciculus gracilis (entire SC)– Fasciculus cuneatus (C1‐T6)
Spinal Cord
Spinal Cord
Spinal Cord
Spinal Cord
Meninges
• Meninges – Dura mater– Arachnoid mater– Pia mater
• Spaces– Subdural space– Subarachnoid space
Meninges• Dura mater
– Dense fibroelastic tissue– Lined with a layer of flat cells
• Arachnoid mater– Fibrous layer– Lined and covered by flat cells– Fibrous strands connect it to
pia mater• Pia mater
– Delicate layer – Covered by mesothelial layer
Meninges
• Suparachnoid space– Contains blood vessels
• When the arteries penetrate the brain tissue it takes with it– Arachnoid mesothelium– Pia mater– Perivascular space
» Continuous with subarachnoid space
Blood Brain Barrier
• protects cells from some toxins and pathogens– proteins & antibiotics can
not pass but alcohol & anesthetics do
• Structure– tight junctions seal
together epithelial cells– continuous basement
membrane– astrocyte processes
covering capillaries
Blood Brain Barrier
• Areas without BBB– Area postrema in the
floor of the fourth ventricle
– Areas in the hypothalamus
• Structure– Endothelial fenestrations
Blood Cerebrospinal Fluid Barrier• Structure
– Endothelial cells– BM of endothelial cells– Pale cells– BM of choroidal epithelial cells
– Tight junctions seal the choroidal epithelial cells