Spinomesencephalic pathway

[4] The anterolateral system (ALS) is a bundle of afferent somatosensory fibers from different ascending tracts in the spinal cord.

[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.

The neurons are either low-threshold of a wide dynamic range, or high threshold,[1] with many of the cells being nociceptive.

[1] 2° (Spinomesencephalic tract → Superior colliculus of Midbrain tectum)