1. Histology of the central nervous system
Prof. Abdulameer Al-Nuaimi
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2. Histology of the gray matter of cerebral hemispheres
Two kinds of neurons can be seen
1- Pyramidal neurons: have apical and basal dendrites, it has an axon arises on the base of the pyramid. The axon divides near to its termination. The axon enters the white matter.
2- Nonpyramidal (granular, stellate) neurons: they are small, multipolar and its branching axon ends within the cortex.
axon

3. Most areas of the cortex have their neurons arranged in six layers
Layer I (molecular layer): is the upper layer of the cortex, situated under the pia mater. This layer contains few nonpyramidal neurons and the apical dendrites of the deeper pyramidal neurons.
Layer II and IV (External and Internal granular layers): They contain numerous nonpyramidal neurons
Layer III and V (External and internal pyramidal layers): They contain pyramidal neurons. In the motor areas, there are very large pyramidal neurons in layer V, called Betz cells
Layer VI (Fusiform layer): Is the deepest layer and adjacent to the white matter. It contains nonpyramidal neurons

4. The pattern of the entering fibres varies from area to area
The pattern of the entering fibres varies from area to area. There are two tangentially placed plexus are present. The outer in layer IV and the inner in layer V The outer layer is very prominent in the visual cortex around the calcarine sulcus and the region is called the Striate area
Cerebral cortex

5. In the sensory areas, the nonpyramidal cells are most numerous
In the motor areas, the pyramidal cells are most numerous and the areas are called agranular cortex.
By using the histological criteria of types of neurons, it is possible to identify the sensory and motor cortex around the central sulcus, visual cortex around calcarine sulcus and the auditory cortex on the superior temporal gyrus.
Other cortical areas are less well defined

6. ganglion cells
Ganglion cells are found in a ganglion.
Ganglion cells are located outside the brain and spinal cord. They form part of the peripheral nervous system. ganglion cells are  either 
1)  pseudounipolar cells of the 
sensory spinal and cranial 
nerves.   
2) Peripheral multipolar motor
neurons 
innervating the
 viscera (visceral or 
autonomic ganglia).

7. Layer III and V Pyramidal layers
Layer II and IV
Nonpyramidal
granular layers
ganglion cell is found in sensory
 ganglion and autonomic
Nervous system
Layer VI
Layer III and V Pyramidal layers

9. Medial side of the cerebral hemisphere

10. White matter of the hemisphere
Nerve fibres of the hemisphere are in three groups
Commissural, association, and projection
1- Commissural fibres: unite corresponding areas of the cortex of the two hemispheres across the midline
They comprise the Corpus callosum, Anterior commissure and
Fornix (Hippocampal commissure)
Corpus callosum: It is the largest white matter structure in the human brain, consisting of 200–250 million axonal projections. It is a broad band of fibres passing between corresponding cortical areas of the two hemispheres. It is located at the base of the median longitudinal fissure (deep groove separates the two hemispheres). In midsagittal section it has a hock shape lying horizontally with a bend anteriorly and a point downward.
The pointed portion is called Rostrum. The bend is Genu

11. The horizontal part is the body
The horizontal part is the body. It has expanded posterior end, the Splenium.
The band extends laterally into each hemisphere. The anterior fibres pass forwards into the frontal poles and are called the Forceps minor.
A thick posterior bundle of fibres pass backwards into the occipital poles, called forceps major.
The rostrum fuses inferiorly with the lamina terminalis.
Anterior commissure: is a bundle of fibres within the lamina terminalis unites the piriform areas and Olfactory tracts of the two sides.
Fornix (Hippocampal commissure): located under the corpus callosum, is made of two crura. The fibres connect the two hippocampi across the midline

12. Medial surface of the cerebral hemisphere
Fornix
Fornix
Mammillary bodies
Frontal lobes
Medial surface of the cerebral hemisphere
Forceps minor
Forceps major
Horizontal section of the brain

13. 2- Association fibres: short and long fibres connecting adjacent or widely separated gyri of the same hemisphere
3- Projection fibres: comprise fibres ascend from or descend to lower lying parts of the central nervous system. Example is the Internal capsule: in horizontal section, it is V shaped, located between the Lentiform nucleus laterally and the thalamus and Caudate nucleus medially.
The anterior limb of the internal capsule contains
a- frontopontine fibres
b- Fibres from the thalamus to the frontal lobe
The posterior limb contains from before backwards
a- Pyramidal fibres (corticonuclear fibres situated at the genu and corticospinal fibres)
b- Somatosensory fibres from thalamus to the postcentral gyrus

14. c- Temporopontine fibres
d- Auditory radiation: from Medial geniculate body superior temporal gyrus
e- visual radiation, from Lateral geniculate body visual cortex
Coronal section of the brain
Horizontal section of the brain

15. Histology of the cerebellum
The cerebellum is a projecting part of the brain above the medulla. The cerebellum consists of a cortex of gray matter and a central core of white matter. The cerebellar cortex contains three well-defined layers, which are, from inside to outside, the granular layer, the Purkinje cell layer, and the molecular layer.
The granular layer is densely packed with granule cells, small neurons whose axons extend into the molecular layer The Purkinje cell layer consists of a single row of Purkinje cells, large neurons with a single axon extending deep into the cerebellum and multiple dendrites branching extensively in the molecular layer The molecular layer contains mostly the axons of granule cells and the dendrites of Purkinje cells. Cells in the molecular layer are primarily glial cells.

16. The molecular layer of the cerebellar cortex contains two types of inhibitory interneuron: stellate (a star-like shape) cells and basket cells. Both stellate and basket cells form GABAergic (Neurons that produce GABA - gamma-Aminobutyric acid-) synapses onto Purkinje cell dendrites.
Nuclei of the cerebellum
The cerebellum has four deep cerebellar nuclei embedded in the white matter in its centre.  the four deep cerebellar nuclei are the dentate, emboliform, globose, and fastigii These nuclei receive Inhibitory (GABAergic) inputs from Purkinje cells in the cerebellar cortex and 
They receive Excitatory (glutamatergic) inputs from mossy fibre and climbing fibre pathways. Most output fibres of the cerebellum originate from these nuclei.

17. Mossy fibres 
Mossy and climbing fibres are fibres coming to the cerebellum. They are one of the major inputs to cerebellum.
There are many sources of this pathway
1- the cerebral cortex, which sends the largest input to the cerebellum via the pontocerebellar pathway.
Other pathways include
2- the vestibular nerve
 and vestibular nuclei
3- the spinal cord
4- the reticular formation

18. Cerebellum

19. Cerebellum

21. A B
Basket neuron
A and B Basket neurons. Basket neurons are named for their widely ramified dendritic trees, which resemble baskets. They are cortical interneurons with axons that spread horizontally to make many inhibitory contacts with the soma (cell body) of other neurons. Distally, each axon breaks up into simple or complex arborizations

22. Thank you