Download Histology Nervous system Nervous system components Divisions

Histology
Nervous system
 Nervous system components
1. Divisions. The nervous system is actually two structurally and functionally
interconnected systems: the central nervous system (CNS), which includes the
brain and spinal cord, and the peripheral nervous system (PNS), which
includes the nerves and ganglia scattered throughout the peripheral portions of
the body.
2. Cells
a. Neurons are the basic cellular elements of the nervous system. Neuron
structure varies tremendously.
1) Motor neurons, which conduct motor impulses from the spinal cord to
skeletal muscles, have cell bodies located in the ventral (anterior)
horns of the spinal cord and axonal terminations on muscle fibers a
meter or more away.
2) Other CNS neurons have a highly complex dendritic arborization; still
others are small interconnecting cells.
b. Glial cells, Such as astrocytes and Schwann cells perform subsidiary
functions unrelated to communication.
3. Synapses are the sites of anatomic and functional interaction between
neurons.
 Central Nervous System (CNS).
 General characteristics
1. The CNS includes the brain and spinal cord. It contains both neurons and glial
cells. The human CMS contains more than 10 billion neurons and
approximately 50 billion glial cells.
2. In some sections of the CMS, neuronal cell bodies form macroscopic clusters
called nuclei, and large bundles of myelinated nerve fibers run together in
tracts.
a. Many functional nuclei in the brain contain vast collections of nerve cell
bodies, axons, dendrites, and glial cells, which form a complex tangle of
processes called the neuropil.
b. The neuropil contains about half of all neuronal cytoplasm in the CNS.
Nerve cell bodies contain the remainder.
3. Functional variations from one CNS region to another are partially due to
variations in the kind of neurons present in each region and to variations in the
organization of communicating processes in the surrounding neuropil.
 Grey matter and white matter
1. The brain and spinal cord contain grey matter, which is relatively rich in
neuronal cell bodies and glia, and white matter, which is relatively rich in
neuronal axon, dendrites, glia, and myelin.
2. In the spinal cord, the centrally located grey matter is divided into anterior
horns (containing motor neurons), intermediate horns (containing autonomic
neurons), and posterior horns (containing sensory neurons). Most grey matter
in the spinal cord is surrounded by white matter.
3. In the brain, the relationship between grey and white matter is slightly
different, due to the presence of superimposed cortical grey matter.
 The components of CNS:
1. The brain: It has a second layer of grey matter (the cortex) that is
superimposed peripherally over the white matter.
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Histology
Nervous system
a. The cerebrum
1) A series of grey matter nuclei, containing numerous neuronal cell
bodies, exists deep in the cerebrum.
a) Large bundles of fiber tracts, consisting largely of neuronal axons,
connect the nuclei.
b) The nuclei are surrounded by a layer of white matter composed of
axons and myelin sheaths derived from oligodendroglial cells.
Numerous axons project both away from and toward the deep
nuclei.
2) The cerebral cortex is a layer of grey matter surrounding the white
matter. It is composed of a peripheral layer of pyramidal neurons and
associated interneurons and glia.
3) Layers of cerebrum
a) Molecular layer: it is the surface layer localize under pia mater.
b) External Granular layer: consists of small neural or pyramidal
cells.
c) External pyramidal layer
1. Consists of cells which have a roughly pyramidal shaped cell
body and a long slender axon projecting from their base.
2. They have numerous dendrites with many long branches and
regions where hundreds of synaptic terminals from other
cortical neurons make contact.
d) Internal Granular layer: consists of small pyramidal or astrocytes
cells.
e) Internal pyramidal layer: the pyramidal cells of this layer are large
and bigger than external pyramidal layer cells.
f) Polymorphic cells layer: consists of different forms of cells except
pyramidal cells.
b. The cerebellum
1) The cerebellar portion of the brain also contains an inner layer of grey
matter, an intermediate layer of white matter, and a cortical (outer)
layer of grey matter.
2) The cerebellar cortex consists of a granular layer, a Purkinje cell layer,
and a molecular layer.
a) The cerebellar cortex is folded into sections called folia, which
enclose central cores of white matter. Adjacent to the white matter
is a granular layer, rich in neurons and glia, which has a highly
cellular appearance.
b) Outside the granular layer is a Purkinje cell layer containing the
cell bodies of Purkinje cells and basket cells. Basket cells surround
the cell body of Purkinje cells.
c) The complex dendritic arborizations of the Purkinje cells project
away from the cell body and into the outermost molecular layer of
the cerebellar cortex. The molecular layer also contains glial cells
and nerve fibers.
2. The spinal cord
a. The central canal is small hole in the middle of the spinal cord lined by
ependymal cells. The central canal contains CSF and communicates with
the ventricles of the brain.
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Histology
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Nervous system
b. Horns of the spinal cord. Transverse sections of the spinal cord reveal
three horns surrounding the central canal.
1) The anterior horns (ventral horns) are paired structures containing the
cell bodies of motor
2) The posterior horns (dorsal horns) are paired structures containing the
cell bodies of sensory
3) The intermediate horns are paired structures containing the cell bodies
of autonomic
c. Meninges. The spinal cord is surrounded by a layer of meninges that are
identical to the meninges of the brain.
Neural ganglia: it is spherical structures surrounded by dense connective
tissue. The ganglia cells are circular, unipolar and contain central nucleus.
1. Type of neural ganglia
a. Root ganglia (sensory)
b. Autonomic ganglia
2. Components of neural ganglia
a. Capsule surrounded the ganglia cells.
b. Inner layer consists of satellite cells.
c. External layer consists of fibrous connective tissue which contain some
fibroblasts.
d. Between cells found connective tissue, fibroblasts and nervous fibers.