Function
This tract carries impulses of crude tactile (protopathic) sensation. The bilateral lesion of this tract leads to loss of crude touch sensation and loss of sensations like itching and tickling. The unilateral lesion of this tract causes loss of crude touch sensation in the opposite side below the level of lesion.
Fig.22. Spinothalamic tracts and pathways for crude touch, pain and temperature sensations. Anterior spinothalamic tract carries crude touch sensation. Lateral spinothalamic tract carries pain and temperature sensations.
LATERAL SPINOTHALAMIC TRACT
Lateral spinothalamic tract is formed by the fibers from the second order neurons of the pathway for the sensations of pain and temperature (Fig.20.).
Situation
This tract is situated in the lateral funiculus towards medial side, i.e. near the gray matter.
Origin
The fibers of lateral spinothalamic tract take origin from substantia gelatinosa of Rolando situated in the posterior gray column. The first order neurons are in posterior nerve root ganglia.
Course
Axons from second order neurons mostly 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 ascend in the lateral column.
All the fibers pass through medulla, pons and midbrain towards thalamus along with the fibers of anterior spinothalamic tract. The fibers of lateral spinothalamic tract form spinal lemniscus along with the fibers of anterior spinothalamic tract at the lower part of medulla. Some of the fibers of lateral spinothalamic tract form collaterals and reach the reticular formation of brainstem.
Termination
The fibers of lateral spinothalamic tract terminate in the ventral posterolateral nucleus of thalamus. From here, third order neuron fibers relay to the somesthetic area of cerebral cortex.
Function
The fibers of this tract carry impulses of pain and thermal sensations. The 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. The bilateral section of this tract leads to loss of pain and temperature sensations on both the sides below the level of lesion.
FASCICULUS GRACILIS (TRACT OF GOLL) AND FASCICULUS CUNEATUS (TRACT OF BURDACH)
The ascending tracts in the posterior white funiculus of the spinal cord are formed by the fibers from posterior root ganglia. Thus, both the tracts are constituted by the fibers of first order neurons of the sensory pathway. The fibers are uncrossed fibers.
Situation
These two tracts are situated in posterior white funiculus of spinal cord. In the cervical and upper thoracic segments of spinal cord, the posterior white funiculus is divided by posterior intermediate septum into medial fasciculus gracilis and lateral fasciculus cuneatus.
Thus, the fasciculus gracilis is situated between posterior median sulcus and posterior median septum on one side and the posterior intermediate sulcus and posterior intermediate septum on the other side.
The fasciculus cuneatus is bound medially by posterior intermediate septum and sulcus and laterally by posterior gray horn, tract of Lissauer and posterior nerve root.
Origin
Fibers of these two tracts are the axons of I order neurons. The cell body of these neurons is in the posterior root ganglia and the fibers form the medial division (bundle) of the posterior nerve root. After entering the spinal cord, the fibers ascend through the posterior white funiculus. These fibers do not synapse in the spinal cord. Some of the fibers of medial division of posterior nerve root descend through the posterior white funiculus in the form of fasciculus interfascicularis or comma tract of Schultze.
Course
The fasciculus gracilis contains the fibers from the lower extremities and lower parts of the body, i.e. from sacral, lumbar and lower thoracic ganglia of posterior nerve root. Fasciculus cuneatus contains fibers from upper part of the body, i.e. from upper thoracic and cervical ganglia of posterior nerve root.