Cerebrum
• Cerebral cortex described as six layered structure.
1. Outer most layer is molecular or plexiform layer-mainly nerve fibers and ſew horizontal cells.
2. External granular layer-contains predominantly stellate cells and few small pyramidal cells.
3. External pyramidal layer-made up of small and medium sized pyramidal cells with few stellate cells.
4. Internal granular layer-made up of stellate cells and few pyramidal cells.
There is a band of white fibers in the middle of this layer called external band of Baillarger
5. Internal pyramidal or ganglionic layer made up of
large pyramidal cells of Betz. In this layer there is thin
band of white fibers called internal band of Baillarger
6. Multiform or pleiomorphic layer with neurons of different sizes and shapes, Cells present are fusiform and cells of Martinotti.
• There is a considerable variation in structure from region to region. In motor cortex pyramidal cells predominate and in sensory cortex stellate cells are more in number
• Pyramidal cells pyramidal in shape with apex towards the surface of cortex. Axon arises from the base.
Cerebellum
•Cortex--three-layered structure.
1. Outer molecular layer contains basket and stellate cells, dendrites of Purkinje cells and parallel fibers of granular cells.
2. Middle Purkinje cell-is single cell layer. These are large flask-shaped cells. Axons from the base of these cells enter medulla and synapse with cells of intracerebellar
nuclei.
3. Inner granular cell layer made up of granule and Golgi cells and synaptic glomerull.
•Synaptic glomeruli formed by dendrites of granule cell, axon terminals of Golgi cell and terminal part of mossy fibers.
• Medulla is made up of white matter.
• Appearance of white matter is described as arbor vitae cerebelli. Made of myelinated nerve fibers.
• In cerebellar cortex only excitatory cell is granule cell. Remaining cells are inhibitory.
• Cerebellum is concerned with balance, co-ordination and muscle tone and posture.
Spinal Cord
•Spinal cord extends from outer margin of foramen magnum to lower border of first lumbar vertebrae. It is part of central nervous system (CNS).
•It has three layers of meningeal coverings-dura mater, arachnoid, pia mater.
•Median anterior fissure is deep.
•Made up of central gray matter and outer white matter
•Central H-shaped gray matter divided into anterior and posterior horns. Lateral horns are seen in thoracic segments.
•Anterior horns are larger than posterior. Contains multipolar motor neurons and interneurons.
•The gray matter of two sides is connected by gray commissure containing the central canal.
•White matter contains ascending and descending tracts. These are grouped as anterior, lateral and posterior columns.