Histology of the CNS Lecture Objectives Describe the

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 billions of 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 (C 8‐L 2) – Intermediolateral cell column (T 1‐L 2, S 2‐S 4) – Medial motor nucleus (entire SC) – Lateral motor nucleus (enlargements) • White mater – Fasciculus gracilis (entire SC) – Fasciculus cuneatus (C 1‐T 6)

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 – –