LATERAL SPINOTHALAMIC TRACT

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.