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Spinomesencephalic pathway
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The spinomesencephalic pathway, spinomesencephalic tract or spino-quadrigeminal system of Mott, includes a number of ascending tracts in the spinal cord, including the spinotectal tract.[1][2][3] The spinomesencephalic tract is one of the ascending tracts in the anterolateral system of the spinal cord that projects to various parts of the midbrain.[1] It is involved in the processing of pain and visceral sensations.[4]
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In the ALS
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Perspective
The anterolateral system (ALS) is a bundle of afferent somatosensory fibers from different ascending tracts in the spinal cord. These fibers include those of the spinomesencephalic tract, spinothalamic tract, and spinoreticular tract amongst others.[5] Spinomesencephalic fibres project to the periaqueductal gray, and to the tectum. Other fibers project to and terminate in the parabrachial nucleus, the pretectum, and the nucleus of Darkschewitsch.[1] The fibers that project to the tectum are known as the spinotectal fibers.[5] The spinotectal tract fibers project to the superior colliculus. Where they synapse onto cells of the deeper superior colliculus they are activated by noxious stimuli.[1]
Anatomy
The spinomesencephalic tract consists mostly of myelinated fibers. The neurons are either low-threshold of a wide dynamic range, or high threshold,[1] with many of the cells being nociceptive.[1]
Origin
Cells of the spinomesencephalic tract arise mostly in Rexed lamina I, and to a lesser extent in Rexed laminae IV and VI-VIII) of the spinal cord. They are mostly concentrated in lamina V.[1] The tract is in the same region as the spinothalamic tract.[1]
Course
Most of the spinomesencephalic fibers decussate to ascend contralaterally, but there is a noted group of uncrossed fibers in the upper cervical levels.[1]
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References
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