Flashcards: Corticobulbar Pathways and Cranial Nerve Control — 24 cards

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.