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The anterior spinothalamic tract (Latin: tractus spinothalamicus anterior) or ventral spinothalamic fasciculus situated in the marginal part of the anterior funiculus and intermingled more or less with the vestibulospinal tract, is derived from cells in the posterior column or intermediate gray matter of the opposite side.
The name dorsal-column medial lemniscus comes from the two structures that carry the sensory information: the dorsal columns of the spinal cord, and the medial lemniscus in the brainstem. There are three groupings of neurons that are involved in the pathway: first-order neurons , second-order neurons , and third-order neurons .
These axons enter the spinal column and penetrate the grey matter of the dorsal horn, where they synapse on second-order neurons in either the substantia gelatinosa of Rolando or the nucleus proprius. Those neurons project their axon to the anterolateral quadrant of the contralateral half of the spinal cord, where they give the spinothalamic tract.
However, the trigeminal lemniscus also carries pain and temperature sensations from the contralateral orofacial region, just as the spinothalamic tract carries these sensations from the contralateral body. Thus, the trigeminal lemniscus of the head is functionally analogous to both the DCML tracts and the spinothalamic tract of the body.
The first-order neurons from the trigeminal ganglion enter the pons and synapse in the principal (chief sensory) nucleus or spinal trigeminal nucleus.Axons of the second-order neurons cross the midline and terminate in the ventral posteromedial nucleus of the contralateral thalamus (as opposed to the ventral posterolateral nucleus, as in the dorsal column medial lemniscus (DCML) system).
The ventral posterior nucleus is divided into: Ventral posterolateral nucleus, which receives sensory information from the body via the medial lemniscus, and spinothalamic tracts. Ventral posteromedial nucleus, which receives sensory information from the head and face via the trigeminal nerve.
The ventral posteromedial nucleus (VPM) is a nucleus within the ventral posterior nucleus of the thalamus and serves an analogous somatosensory relay role for the ascending trigeminothalamic tracts as its lateral neighbour the ventral posterolateral nucleus serves for dorsal column–medial lemniscus pathway 2nd-order neurons. [1]
The pathway then projects down into the posterior grey column of the spinal cord, inhibiting pain sensation transmission. Oculomotor nerve nucleus: This is the third cranial nerve nucleus. Trochlear nerve nucleus: This is the fourth cranial nerve. Red nucleus: This is a motor nucleus that sends a descending tract to the lower motor neurons.