Histology of Central Nervous System

1. Histology of Central Nervous System

2. Introduction • Central nervous system (CNS) – Brain and spinal cord • Peripheral nervous system (PNS) - cranial nerves and spinal nerves

3. Protective layers of CNS • Nervous tissue is very delicate – protected by bones, connective tissue layers and CSF. • Connective tissue coverings – Meninges • Dura mater, arachnoid mater and pia mater • Subarachnoid space - CSF

4. Cerebrospinal fluid • Clear, colourless fluid • Acts like cushion for brain and spinal cord • Produced by choroid plexus in lateral, third and fourth ventricles • Absorbed via arachnoid villi into venous blood of the superior sagittal sinus • Arachnoid villi are small extensions of arachnoid layer which is projected into venous sinuses of dura mater.

5. Morphology of a typical neuron

6. Types of neurons in the CNS • Multipolar – brain and spinal cord • Bipolar- Retina of eye, inner ear, olfactory epithelium • Unipolar/pseudounipolar – craniosacral ganglia

7. Grey matter and white matter • Grey matter – neurons, dendrites and neuroglial cells • White matter – myelinated axons

8. SPINAL CORD

10. Spinal cord is the lowerelongated part of CNS. • Cylindrical in shape. • 45 cm in length. • 30 gm in weight.

11. Extension • From upper border of first cervical vertebra to the lower border of first lumbar vertebra. • Conus medullaris. • Filum terminale.

12. Meninges

13. Extension of meninges

14. Features of spinal cord

16. Spinal nerve

17. Shape of the spinal cord sections

18. Shape of the cervical segment Spinal cord, cerebrum & cerebellum

19. Shape of the thoracic segment

20. Shape of the lumbar segment

21. Shape of the sacral segment

23. Grey matter of spinal cord & brain

24. CEREBRUM

25. INTRODUCTION In the cerebrum the grey matter lies superficial to the white matter. • Grey matter • Collection of cell bodies of neurons, neuroglia and blood vessels. • Appears grey because it does not contain much myelin. • White matter • Contains bundles of nerve fibres. • White appearance is due to the myelin sheath around the fibres.

26. Types of cells in cerebrum • Pyramidal cells • Stellate cells • Fusiform cells • Horizontal cells of Cajal • Cells of Martinotti

28. Pyramidal cells • Cell body is triangular in shape • Large vesicular nucleus. • Size:- 10 -120 microns • Apical dendritic end faces the surface of the cerebrum • Dendrites originate from all 3 angles • Axon is given off at the base and extends to deeper layers Granular [stellate] cells • Star shaped • Size- 8 microns • Their processes extend only into the neighbouring areas

29. Fusiform cells • Long axis vertical to the surface • Seen mostly in the deepest layers of cortex • Dendrites arise from each pole of the body • Axon arises from inferior aspect of the body • Horizontal cells of Cajal • Small, fusiform, horizontally oriented • Found in most superficial layers of cortex • Dendrite emerges from each end. • Axon runs parallel to cortex. • Cells of Martinotti • Small, multipolar, present throughout the cortex. • Axon directed towards pial surface.

30. LAYERS OF CEREBRUM • 6in number • Named on basis of predominance of cell type. • Distinction between layers is not well marked.

31. Layers of cerebrum • Named from superficial to deep • They are:- • The molecular [ plexiform layer] • External granular layer • External pyramidal cell layer • Inner granular layer • Inner pyramidal [ganglionic] layer • Pleiomorphic [polymorphic] layer

36. MOLECULAR LAYER • Also called plexiform layer • Just beneath piamater • Contains horizontal cells of Cajal. • The processes of horizontal cells. • EXTERNAL GRANULAR LAYER • Contains :- • small pyramidal cells • granular cells • Their apical dendrites extend into the 1st layer and their axons end in the deeper layers.

37. EXTERNAL PYRAMIDAL LAYER • Contains :- • medium sized pyramidal cells • some scattered granular cells • INNER GRANULAR LAYER • A thin layer • Densely packed granular cells • White horizontal fiber layer called external band of Baillarger /white stria (prominent in visual cortex).

38. INNER PYRAMIDAL [GANGLIONIC] LAYER • Contains-largest pyramidal cells [Betz cells] • Few non-pyramidal cells • granular cells • Martinotti cells • Horizontal fibres in the deeper part called internal band of Baillarger. • PLEIOMORPHIC LAYER • Contains neurons of different shapes like pyramid, spindle and ovoid. • Many nerve fibres entering and leaving the underlying white matter.

39. MOTOR CORTEX • Predominantly pyramidal cells in layers III & V • The pyramidal cells are densely packed and large. • SENSORY CORTEX • Very few pyramidal cells in layers III & V • Most layers have small granular cells

41. Cerebellum

42. Location: posterior cranial fossa behind Pons & medulla oblongata (MO) fourth ventricle separates cerebellum from Pons & MO

43. EXTERNAL FEATURES

44. Inferior Olivary Nucleus Mossy Fibers Climbing Fibers Afferents CEREBELLUM Efferents Thalamus Vestibular Complex Red Nucleus

47. Microscopic structure Grey matter Neurons are arranged in 3 layers 1. outer molecular layer consist of cell bodies of stellate & basket cells 2. intermediate layer consist of cell bodies of purkinje cells 3. inner granular layer consist of cell bodies of granule cells, Golgi cells, & their processes

49. Summary

50. Spinal cord