brain histology

l Nerve cells/neurons
Oligodendrocytes, Astrocytes, Ependymal cells,
Microglia Special glial cells - (CNS)
2 Glial cells|
Schwann cells, Satellite/Capsule cells,
Enteric (gut) glia - (PNS)
3 Blood vessels
4 Connective tissue enclosing sheaths 
ELEMENTS OF NERVOUS SYSTEM
 
NEURONS  : Pseudounipolar:one process branching into two a short way from the cell soma, e.g., dorsal-root ganglion cell
Bipolar cells processes come off from opposite poles of the cell, and the cell then assumes a spindle shape
Multipolar cells :
stellate or star-like, pyramidal with apical and basal dendrites, Purkinje with a plump body tapering to an espalier-oriented dendritic tree

NEURONS
Neuron , Axis-cylinder process = Axon 
Protoplasmic processes = Dendrites
Body of the nerve cell = Soma
 
Nerve Cell 
Neuron
Neuron 
Body of the nerve cell = Soma

Soma contains a large central nucleus with little chromatin. The nucleolus is prominent because the neuron has to synthesize organelles and cytoplasm to fill its long processes
Around the nucleus is the perikaryon with:  

(a) Nissl bodies/granules - basophilic, cytoplasmic structures are concentrations of granular ER. 
(b) Neurofilaments - a variety of intermediate filament - are aggregated into neurofibrils visible in the cytoplasm after silver impregnations. 
(c) Surrounding the nucleus are elements of the Golgi apparatus, mitochondria, lysosomes, and microtubules. Actin filaments move vesicles in the zone directly under the neuron's plasmalemma. 
(d) Pigment is sometimes present, e.g., melanin in substantia nigra neurons, and lipofuscin in old neurons. 
(e) Cell membrane has specialized receptive areas, the subsynaptic membranes of synapses.  
 
Synapses 
A junction that mediates information transfer from one neuron:
To another neuron
To an effector cell
Presynaptic neuron – conducts impulses toward the synapse
Postsynaptic neuron – transmits impulses away from the synapse
 
Cell to Cell Conduction: the Synapse

Cell to Cell Conduction: the Synapse 
Electrical synapses: gap junctions
Very fast conduction
Example: cardiac muscle
Chemical synapses
Pre synaptic terminal
Synthesis of Neurotransmitters (L-glutamate, GABA, dopamine, serotonin, acetylcholine, noradrenaline and glycine OR "minor" transmitters such as cholecystokinin, endogenous opioids, somatostatin, substance P …)
Ca2+ releases Neurotransmitters
Synaptic cleft
Postsynaptic cell: Neurotransmitter receptors

Astrocytes :Protoplasmic astrocytes: large, star-shaped with many processes, some of which attach pedicels to blood vessels or the basal lamina under the pia mater; have cytoplasmic filaments and microtubules; are common in grey matter.
Fibrous astrocytes: similar to protoplasmic astrocytes, but have more filaments and glycogen, and lie in the white matter
Astrocytes 
Fibrous Astrocytes (Objective 40x) 
Astrocytes in BBB

Astrocytes: 
 Provide physical support to neurons 
Clean up carcasses of dead neurons 
Provide controlling chemicals to neurons 
Play important role in providing nourishment to neurons 

Oligodendrocytes 
= oligodendroglia: plump cell body with fairly dense cytoplasm and a darker nucleus and fewer, shorter processes than an astrocyte; common in white matter, but some are perineuronal Provide physical support to neurons Produce myelin sheath that insulates axons


Microglia  
(a) derived from mesenchyme via bone marrow; 
(b) potentially phagocytic; 
(c) dispersed throughout the brain; 
(d) a small elongated cell with many short processes and a dark nucleus.This is the ramified or resting microglial cell, which becomes round and phagocytic as a reactive microglial cell (Gitter cell), when responding to damage
 
Clean up CNS debris 
Play role of immune system in brain  
(similar to microphages in blood)
 Functions: Ependymal cells lining ventricles, and covering the choroid plexus, they are typically cuboidal and often have cilia 
Ependymal cells  : Form a relatively permeable barrier between CSF and the tissue fluid that surrounds the cells of the CNS. In certain region of the brain ependymal cells possess cilia, the beating of which help to circulate the CSF.  Modified ependymal cells contribute to the formation of the choroids plexus which is a capillary knot that protrudes into a brain ventricle, and is involved in the synthesis of cerebrospinal fluid. 

 
Cerebral neocortex :
The number of layers to be clearly seen depends on the particular area of the cerebral cortex and the criteria of the investigator. Thus Cajal worked with an 8-layered scheme, whereas Brodmann adopted 6 - today's choice. Even so, in the motor region only 5 are to be easily made out. 

Cerebral Cortex 
I: plexiform (molecular): dendrites and axons of cortical neurons making synapses; neuroglia and rare horizontal cells 
II: outer granular: dense population small pyramidal cells and stellate cells [small neurons]; various axons and dendritec connections 
III: (outer) pyramidal cell: moderate size; increasing size deeper 
IV: inner granular: densely packed stellate cells 
V: ganglionic or inner pyramidal: lg pyramidal cells (including Betz cells) and smaller numbers of stellate cells and small neurons 
VI: multiform (fusiform) cell: numerous small neurons, small pyramidal cells, stellate cells, especially superficially and fusiform cells in deeper part.

Cerebral Cortex 
I: plexiform 
II: outer granular
III: (outer) pyramidal cell
IV: inner granular
V: ganglionic or inner pyramidal
VI: multiform (fusiform) cell