Neuro-Histology 1

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cells of the CNS

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neurons
neuroglia (insterstitial cells)

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specialized for:
excitation/inhibition
impulse conduction

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neurons

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astrocytes
oligodendrocytes
microglia (mesoglia)
ependymal cells

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neuroglia

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cell bodies of neurons embedded in a neuropil made up of unmyelinated cell processes plus glial cells

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gray matter

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group/cluster of nerve cell bodies w/ similar function

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nucleus

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group/cluster of nerve cell bodies w/ similar functions outsid CNS

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ganglion

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gray matter location

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central part of spinal cord
brain stem
cortical tissue (of brain)

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long processes of neurons (myelinated) plus glial cells; functional related processes grouped in TRACTS

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white matter

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neuron cell bodies plus myelinated cell process plus glial cells; includes portions of brain stem

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mixed areas

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CNS appearance

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gray matter
white matter
mixed areas
capillaries
no CT fibers except some associated w/ capillaries

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cell body (perikaryon) nucleus

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usually central except for neurons of autonomic nervous system (eccentric nuclei)
chromatin extended (lots of euchromatin)
single, large nucleolus

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cell body Nissl substance

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identified by light microscope as blue patches
stacks of flattened cisternae of rough ER mixed w/ free ribosomes
chromatolysis-following nerve injury, there is dissolution of Nissl substance
located in perikaryon and dendrites (not axons)

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contains golgi mitochondria, microfilaments, microtubules

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cell body (perikaryon)

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cell body pigments

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lipofuscin-increases w/ age of cell
melanin-abundant in substantia nigra of midbrain

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axon characteristics

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variable size
many have collateral branches which leave at right angles (some have recurrent collaterals that curve back along originating axon)
axon hillock-proximal, thicker part of axon
axolemma-plasmamembrane of axon
axoplasm-cytoplasm of axon (lacks golgi and rER)

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classification of neurons

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shape
size

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shape of neurons

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multipolar
bipolar
unipolar
pseudounipolar

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many dendritic processes +1 axon
includes most neurons

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multipolar

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2 processes-1 dendrite +1 axon
located in inner ear, retina of eye

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bipolar

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1 axon only
located in retina of eye

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unipolar

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modified unipolar-axonal process + dendritic process
somatic sensory fibers

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pseudounipolar

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large neurons (golgi type I)

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bigger diameter
longer axons
examples:pyramidal cells, purkinje cells (cerebellar cortex), lower motor neurons

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apical dendrite (extends toward cortical surface)
several basal (horizontal) dendrites
axon arises from base
Betz cells of motor area of cerebral cortex

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pyramidal cells (cerebral cortex)

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flask-shaped
1-2 dendrites extend toward surface (lots of branching)
axon from base of perikaryon passes deep into cerebellum

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purkinje cells (cerebellar cortex)

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located in ventral horns of spinal cord and motor nuclei of cranial nerves

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lower motor neurons

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small neurons (golgi type II)

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smaller diameter
shorter axons (usually unmyelinated)
outnumber golgi type I cells
includes interneurons (internuncials)
examples: stellate cell (cerebral cortex), cell of martinotti, granule cell, horizontal cell

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cerebral cortex
axon ends on one or more cells in the area

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stellate cell (cerebral cortex)

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cerebral cortex
resembels stellate; has longer axon which is directed toward cortical surface

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cell of martinotti

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located in deepest of 3 layers of cerebellar cortex

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granule cell

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cerbral cortex
long axis is parellel to cortical surface
located in retina

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horizontal cell

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spherical nucleus w/ medium-dense chromatin
numerous cytoplasmic processes project from cells to wrap around axons (forms myelin sheath)
disposed in rows b/t axons in white matter; appear to be randomly located in gray matter

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oligodendrocytes

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largest nuclei of glial cell (irregular shape)
contain many processes that project in several directions
contain lots of microfilaments (for rigidity)
ends of processes widen and spread over surfaces of neurons and capillaries

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astrocytes

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astrocyte function

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support
chemical transport (b/t capillaries and neurons)

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astrocyte types

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fibrous-white matter
protoplasmic-gray matter

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line ventricles of brain and central canal of spinal cord
cuboidal-columnar shape
ciliated in ventricles, non-ciliated elsewhere

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ependymal cells

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small cells w/ dark, flattened nuclei
2 schools of thought on origin and function

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microglia

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neuropil light microscope

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appears as fine mottle area b/t cell bodies of neurson

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neuropil electron microscope

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conglomerate of cell bodies and processes of astrocytes along w/ precesses of neurons (mostly unmyelinated)
fine intercellular spaces b/t cells and their processes
GAGS (hyaluronic acid, chondroitin and heparin sulfates) present in spaces