LATERAL SPINOTHALAMIC TRACT
Lateral
spinothalamic tract is formed by the fibers from second order neurons of
the pathway for the sensations of pain and temperature.
Situation
Lateral
spinothalamic tract is situated in the lateral column towards medial side, i.e. near the gray matter.
Origin
Fibers of lateral
spinothalamic tract take origin from two sources:
i.
Marginal nucleus
ii.
Substantia gelatinosa of Rolando.
Course
Lateral
spinothalamic tract has crossed fibers. Axons from
marginal nucleus and substantia
gelatinosa of Rolando cross to the opposite side and reach the lateral column of same segment. Few fibers may ascend one or two
segments, then cross to the opposite side and then
ascend in the lateral column.
All the
fibers pass through medulla, pons and midbrain and reach thalamus along with
fibers of anterior
spinothalamic
tract. Some of the fibers of lateral spinothalamic tract form collaterals
and reach the reticular formation of brainstem. Fibers
of lateral spinothalamic tract form spinal lemniscus along with the fibers of anterior spinothalamic tract at the lower part of medulla.
Termination
Fibers of lateral
spinothalamic tract terminate in the ventral posterolateral nucleus of thalamus along
with
anterior
spinothalamic tract fibers. From here, third order neuron fibers run to
somesthetic area (sensory
cortex) of
cerebral cortex.
Function
Fibers of lateral
spinothalamic tract carry impulses of pain and temperature
sensations. Fibers arising from this
marginal nucleus transmit impulses of fast pain sensation.
Fibers arising from substantia gelatinosa of Rolando transmit impulses of
slow pain and temperature sensations.
Effect of Lesion
Bilateral lesion of this
tract leads to total loss of pain and temperature sensations on both sides
below the level of lesion. Unilateral lesion or
sectioning of the lateral spinothalamic tract causes loss of pain (analgesia) and
temperature (thermoanesthesia) below the level of lesion in the opposite side.
VENTRAL
SPINOCEREBELLAR TRACT
Ventral spinocerebellar
tract is also known as Gower tract, indirect spinocerebellar tract or anterior
spinocerebellar tract. It is constituted by the
fibers of second order neurons of the pathway for subconscious kinesthetic
sensations.
Situation
This tract is situated in lateral
white column of the spinal cord along the lateral periphery.
Origin
Fibers of this tract arise
from the marginal nucleus in posterior gray
horn. Neurons of marginal nucleus
form the
second order neurons. Fibers from these neurons make their first
appearance in lower lumbar
segments of spinal cord. First order neurons are in the posterior root ganglia and receive the impulses of proprioception from the proprioceptors in muscle, tendon and joints. Fibers
from neurons of posterior root ganglia reach the marginal
cells through posterior nerve root.
Course
Ventral spinocerebellar
tract contains both crossed and uncrossed fibers. Majority of the fibers from the
marginal nucleus cross the
midline and ascend in lateral white column of opposite
side. Some fibers
ascend in the lateral
white column of the same side also. These nerve fibers
ascend through other spinal
segments,
medulla, pons and midbrain Finally, the fibers reach the cerebellum through the
superior cerebellar peduncle.
Termination
These
fibers terminate in the cortex of anterior lobe of cerebellum.
Function
Ventral spinocerebellar
tract carries the impulses of subconscious kinesthetic
sensation (proprioceptive
impulses
from muscles, tendons and joints). Impulses of subconscious kinesthetic
sensation are also called non-sensory
impulses.
Effect of Lesion
Lesion of
this tract leads to loss of subconscious
kinesthetic
sensation in the opposite side. all the segments of spinal cord and
terminate on the lateral vestibular nucleus. This tract is also
concerned with proprioception.
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