1 - Internal Anatomy of Brainstem (Motor) Flashcards
Pyramidal Motor System
Corticospinal vs Corticobulbar bs Corticopontine
Corticospinal: Descends through entire brainstem, terminates in spinal cord
Corticobulbar: Terminates in motor nuclei (pons, medulla)
Corticopontine (Extrapyramidal): Terminates in pontine nuclei
Corticospinal Pathway
Origin?
Pathway?
Function?
Origin: Primary motor cortex (w/premotor, supplementary motor, somatosensory)
Pathway: UMN pass through internal capsule into crus cerbri, basal pons, pyramids; axons terminate on ventral horn motor neurons
Function: Initiate voluntary movements mediated by spinal cord LMN
What is this structure, and its function?
Red Nucelus
Not part of corticospinal pathway
Prominent landmark at level of superior colluculli
Color due to iron
Receives cortical and cerebellar input
What occurs to the Corticospinal axons in the basal pons?
They separte into large bundles (fascicles), located centrally
Bundles of fibers (photo) can indicate position
What occurs to the Corticospinal Pathways fascicles below pons?
What is the orientation during descent?
They join to form pyramids basal pons , located medial and ventral
Remain ipsilateral until they hit the pyramidal decussation
Pyramidal Decussation
Junction of medilla and spinal cord; site of cross over in the Corticospinal pathway
Corticobulbar Pathway
**primarily involved in carrying the motor function of the non-oculomotor cranial nerves**
- originates form face and head area of primary motor cortex
- UMN accompandy corticospinal fibers through internal capsule, crus cerebri, basal pons, pyramids
- Axons terminate brainstem motor nuclei:
Motor Nucleus - CN V
Facial Motor Nucleus - CN VII
Nucleus Ambiguus - CN IX, X
Hypoglossal Nucleus - CN XII
*Innervation may be bilateral, or predominantly ipsi or contra lateral
initiate voluntary movements mediated by brainstem LMNs
Corticobulbar Pathway
Innervation
Exceptions
Innervation:
- General Rule = bilateral innervation (damage will NOT cause weakness on either site, you have two)
Exceptions:
- Facial Motor Nucleus - LMNs for lower half of face receive contralateral input
- Hypoglossal Nucleus - LMNs for genioglossus receive contralateral input
Lesion of Facial Motor Nucleus:
UMN
LMN
UMN: Lesion causes paralysis of muscles of lower face on side opposite lesion; mouth droop, central facial paralysis or central 7
LMN: Lower half of face receive contralateral input
**Whole face = lower, half face = upper**
Lesion of UMN of Hypoglossal Nucleus
LMNs: Innervate genioglossus receive contralateral input
UMN: Cause paralysis of side opposite lesion
Protruded tongue deviates from side of lesion
**UMN = NO atrophy, NO fasciculations**
Medial Longitudinal Fasciculus
Pathway?
Functions?
Pathway: Links nuclei controlling extraocular muscles with horizontal and vertical gaze centers, vestubular nuclei, spinal cord
Functions: Conjugate Eye Movements (connects eye muscles), Vestibulo Ocular reflex pathways, Vestibulo Spinal reflex pathways
Vestibulospinal Pathway
Origin
Major Functions
Components
Origin: Vestibular Nuclei
Major Functions: Maintain posture against gravity, vestibulospinal reflexes
Components: Medial (to cervical spinal levels, movement of head/neck), Lateral (to all spinal slevels, movement of trunks/limbs)
Medial Vestibulospinal Tract (VST)
Origin
Major Functions
Components
Origin: Medial vestibular nucleus, descends bilaterally in MLF
Major Functions: Facilitiates reflexes and tone for muscles of neck
Components
Lateral Vestibulospinal Tract (VST)
Origin
Major Functions
Components
Origin: Lateral vestibular nucleus
Major Functions: Facilitates reflexes and tone for antigravity (extensor) muscles
Clinical: Decorticate Posturing
Cause?
Symptoms?
Caused by large lesions of cerebral hemispheres (supratentorial lesion) – Loss of cortical inut to motor systems
Symptoms: Upper Limb Flexion, Lower Limb Extension
Lower Extension - Vestibulospinal Pathway
Upper Flexion - Rubrospinal Pathways
**May convert to decerebrate posturing if lesion expands through tentorial notch
Decerebrate Posturing
Cause?
Symptoms?
Cause: Large lesion of cerebral hemispheres (supratentorial lesion) that expands into midbrain, rostral pons
Loss of cortical input to motor systems
Loss of activity in rubrospinal pathway
Symptoms: Upper and Lower limb extension; Unopposed activity in vestibulospinal pathways
Autonomic Pathways through Brainstem
Clinical Relevance?
Hypothalamus major center of higher control for autonomic nervous system
Pathway is poorly defined
Clinical:
Lesions affecting the ALS also can cause Horner’s Syndrome
Sympathetic fibers through to travl close to ALS (lateral location)
