The neural control of orienting: role of multiple-branching reticulospinal neurons

This chapter emphasizes the functional significance of the multiple-branching patterns of descending axons implicated in the control of movement. The example provided concerns orienting head movements, which are controlled by pathways from the superior colliculus (SC). Such control is mediated via cervical reticulospinal neurons (C-RSNs), which take origin in the nucleus reticularis pontis caudalis and nucleus reticularis gigantocellularis, and give off multiple collaterals along the full length of their axonal trajectory. Their projection is not only to lamina IX neck motor nuclei in upper cervical segments, but also to laminae VII-VIII in lower cervical segments. Thus, SC commands for head orienting are transmitted to both neck motoneurons and lower cervical spinal circuitry, which latter network controls appropriate postural adjustments by the coordinated control of motoneurons supplying the four limbs.