NETTER - Neuroscience Flash Cards

Corticobulbar Tract
1. Primary motor cortex (Area 4)
2. Genu of the internal capsule
3. Oculomotor nucleus
4. Trochlear nucleus
5. Abducens nucleus
6. Trigeminal motor nucleus
7. Facial nucleus to the upper face
8. Facial nucleus to the lower face
9. Hypoglossal nucleus
10. Nucleus ambiguus
Comment: The corticobulbar tract arises mainly from the lateral
portion of the primary motor cortex (Area 4). Corticobulbar axons
project through the genu of the internal capsule, cerebral peduncle,
basis pontis, and medullary pyramids on the ipsilateral side.
Corticobulbar axons terminate in the cranial nerve motor nuclei on
both sides except for the portion of the facial nucleus that distributes
to muscles of the lower face; that nucleus receives exclusively
contralateral projections. Therefore, a corticobulbar tract lesion (such
as occurs with a stroke affecting the genu of the internal capsule, or
a cerebral peduncle lesion) results in a contralateral drooping lower
face whose muscles cannot contract on command (central facial
palsy). This can be distinguished from a peripheral facial palsy (Bell’s
palsy), which demonstrates total facial paralysis of both upper and
lower musculature. In some patients the corticobulbar projections to
the hypoglossal nucleus are mainly contralateral, and to the spinal
accessory nucleus are mainly ipsilateral; however, these anatomical
observations usually are not accompanied by long-term functional
consequences.
Systemic Neuroscience See book 15.6