Dorsal root ganglia
Dorsal root ganglion has
different name like : spinal
ganglion/ posterior root
ganglion
It is a cluster of neuron (a ganglion)
in a dorsal root of a spinal nerve.
The cell bodies of sensory neurons known as first-order neurons are located in the dorsal root ganglia
Gross information
The axons of
dorsal root ganglion neurons are known as afferents.
In the peripheral nervous system,
afferents refer to the axons that relay sensory information into
the central nervous system (i.e. the brain and
the spinal cord).
These neurons are of
the pseudo-unipolar type, meaning they have an axon with two branches
that act as a single axon, often referred to as a distal process and
a proximal process.
Unlike the majority of
neurons found in the central nervous system, an action
potential in posterior root ganglion neuron may initiate in the distal
process in the periphery, bypass the cell body, and continue to
propagate along the proximal process until reaching
the synaptic terminal in the posterior horn of spinal cord.
Histology of dorsal root gangliaon
Connective
tissue capsule
The sensory
ganglion is covered by the vascular connective tissue capsule which also
envalops its sensory root . the collagenous connective tissue septa penetrate
the ganglion.
Neurons
The somata
of these cells are pseudounipolar which is spherical in shape with large nuclei
and nucleoli
Note that
some somata are large and while others are small . so nuclei of somata are not
always in the plane of section.
In hematoxylin and eosin stain the somata is
more or less homogenous and pink so the organelles such as Nissl substance are
not visible.
Each soma is
surrounded by neuroectodermally derived capsule cells.
Capsular
cells are much smaller than small sized somata of neuron and contain small ,
round nuclei.
The smallest
cells of ganglion are Satelline cells or fibroblast are also evident . they are small , elongated
contain densely stain nuclei and
situated peripheral to the capsular cells
Synapses do
not occur in the ganglion
Fibres
Fibres are
mostly myelinated and travel in bundles through the sensory ganglion. They
belong to the large pseudounipolar neurons.
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