See also: ANATOMY OF GAZE & FIXATION
Abducens nuclei
The paired abducens nuclei are found medio-dorsally at the level of the pontomedullary junction, immediately lateral to the medial longitudinal fasciculus.
- About 70% of the neurons arising from each abducens nucleus are motor neurons that form the abducens nerve fascicles and innervate the ipsilateral lateral rectus muscle.
- Approximately 30% are internuclear neurons that are involved in the control of the conjugate gaze.
- A small percentage of neurons project to the cerebellar flocculus, and play a role in gaze holding.
The parapontine reticular formation (PPRF) is activated by the contralateral frontal eye field, and in turn it activates the adjacent abducens nucleus via excitatory burst neurones. Horizontal gaze is then mediated by abducens motor neurones to the ipsilateral lateral rectus muscle and via excitatory abducens interneurones, which decussate before ascending in the MLF to the medial rectus subnucleus of the contralateral oculomotor nucleus1.
Figure 1. The pontomedullary junction showing the important structures for horizontal gaze (PPRF, 6th nerve N.), and for gaze-holding (N Prepositus Hypoglozzi, Medial Vestibular N).
