4. Origin
• Abducens nucleus originates from the tegmenum
pontis at the level of facial colliculus.
• The nucleus is located;
1. anterior to the 4th ventricle,
2. posterior to the medial leminiscus,
3. Lateral to the medial longitudinal fasciculus, &
4. Medial to facial nerve & trigeminal spinal nucleus.
• The facial colliculus is a focal bulge in the floor of
the fourth ventricle formed by looping fibers of the
facial nerve around the abducens nucleus.
8. The abducens nucleus contains 3 types of
neurons:
1. Abducens motor neurons which innervate the ipsilateral lateral rectus
muscle.
2. Abducens internuclear neurons, which project to the contralateral medial
rectus subnucleus of the oculomotor nucleus via the medial longitudinal
fasciculus.
3. Neurons that project to the cerebellar flocculus
9.
10. Central course
• The abducens nerve fascicle course
antero-inferiorly through the pontine
tegmentum adjacent to the facial nerve
and exit from the brain stem at the ponto-
medullary sulcus.
11. Intracranial course
Dorello's canal is an osteofibrous conduit located at the
level of the petrous apex through which the abducens
nerve courses to reach the cavity of the cavernous sinus
• Cisternal segment
• Petro-clival segment
• Cavernous segment
• Orbital segment
12. Cisternal segement
• courses superiorly through the prepontine cistern, to
pierce the dura over medial most aspect of the petrous
ridge.
15. Petroclival segment
Dorello's canal is an osteofibrous conduit
located at the level of the petrous apex
through which the abducens nerve courses
to reach the cavity of the cavernous sinus
16.
17. Cavernous segment
The cavernous segment of the abducens nerve lie
within the body of the sinus unlike the oculomotor ,
trochlear & V1 & V2 divisions of the trigeminal
nerve which lie within the lateral wall of the sinus.
40. Usher syndrome
• Dilatation of the subarachnoid spaces
surrounding the cranial nerves with
petrous apex cephaloceles in Usher
syndrome.
• Usher syndrome is an autosomal
recessive disorder characterized by
retinitis pigmentosa & congenital SNHL.
44. One & half syndrome
• Complete horizontal gaze palsy,
when looking toward the side of the lesion.
• Half gaze palsy,
when looking toward the opposite side.