Origin of corticobulbar tract
Mainly from primary motor cortex (BA4), especially lateral-inferior part.
Cortical motor areas — primary
Primary motor cortex (BA4) in precentral gyrus, executes voluntary movements.
Cortical motor areas — premotor
Premotor cortex (BA6), involved in movement planning and selection.
Cortical motor areas — SMA
Supplementary motor area (BA6), coordinates bilateral movements.
Cortical motor areas — somatosensory
Primary somatosensory cortex (BA3,1,2), provides sensory feedback.
Destination nuclei — CN V
Trigeminal nucleus, controls mastication muscles.
Destination nuclei — CN VII
Facial nucleus, controls mimic muscles; bilateral upper face, contralateral lower face.
Destination nuclei — nucleus ambiguus
Controls muscles of speech/swallowing; bilateral innervation.
Destination nuclei — CN XII
Hypoglossal nucleus, tongue muscles; upper bilateral, lower contralateral.
Pathway of corticobulbar fibers
From cortex, through corona radiata, genu of internal capsule, crus cerebri, brainstem to nuclei.
Bilateral innervation — facial muscles
Upper face: bilateral; lower face: contralateral corticobulbar input.
Tongue muscle innervation — upper hypoglossal
Bilateral corticobulbar input to most tongue muscles.
Tongue muscle innervation — lower hypoglossal
Contralateral corticobulbar input to genioglossus.
Functions of corticobulbar
Controls muscles for speech, swallowing, facial expression.
Clinical lesion — Bell's palsy
Ipsilateral facial paralysis including forehead; peripheral nerve lesion.
Clinical lesion — corticobulbar
Contralateral lower facial paralysis; forehead spared in central lesions.
Origin of corticospinal tract
Mainly from primary motor cortex (BA4), premotor, SMA, and S1.
Corticospinal pathway course
From cortex through corona radiata, internal capsule, crus cerebri, decussates at pyramids.
Lateral vs anterior corticospinal
Lateral decussates at pyramids, controls limbs; anterior remains ipsilateral, controls axial muscles.
Descending tracts overview
Includes corticospinal, corticobulbar, rubrospinal, vestibulospinal, reticulospinal.
Lateral corticospinal — function
Controls distal limb muscles for fine voluntary movements.
Anterior corticospinal — function
Controls axial and proximal muscles for posture.
Decussation percentage
80-85% decussate at pyramids; 15-20% remain ipsilateral.
Collateral fibers from corticospinal
Project to cranial nerve nuclei for facial, tongue, pharyngeal muscles.
Testez vos connaissances avec un QCM de 12 questions sur Corticobulbar Pathways and Cranial Nerve Control.
1. The origin of the corticobulbar tract is best identified as which of the following cortical areas?
2. What percentage of the corticobulbar tract is contributed by the primary motor cortex (BA4)?
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