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The dorsal (rear) root is the sensory
root. The ventral (front) root is the motor root.
The dorsal root ganglion contains cell
bodies of general somatic afferent (inbound) neurons, mediates pain
and temperature and synapse in the dorsal horn of the spinal cord.
A-delta
fibers are myelinated (insulated with a myelin sheath). The pain
is fast and well localized, like the initial prick or stinging sensation
following an injury.
C fibers
are nonmyelinated and smaller than A-delta fibers. They transmit
pain much slower. The pain is more lasting, generalized and described
as a dull ache.
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Dorsal Root
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Ventral Root
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Synonym:
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back
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front
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Role:
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sensation
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movement
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Nerve Diameter:
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0.25 - 1.5 µm
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1.00 - 5.0 µm
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Signal Rate:
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0.25-1.5
m/s
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6 - 10 m/s
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Diameter:
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0.25 - 1.5 µm
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1.00 - 5.0 µm
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Sensation Speed:
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Slow
Pain
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Fast Pain
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Duration:
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Lasting
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Stinging
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Sensation Region:
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Generalized
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Localized
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Sensation Type:
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Dull Ache
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Prick
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Fiber Type:
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non-
myelinated
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myelinated
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Thalamocortical fibers from neurons in
the thalamic nuclei relay pain information to the cerebral cortex.
Painful stimuli originating in the periphery
decussate (cross) and ascend in the contralateral (opposite side)
spinal thalamic tract.
The lateral spinal thalamic tract is the
main tract carrying general somatic afferent fibers to their central
nervous connections.
Peripheral
receptors are terminals of pain pathway fibers. (A-delta and C nerve
fibers.)
This process is referred to as nociception.
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