25 - NeuroAnatomy - Motor Pathways Flashcards
Which two structures regulate descending cortical and descending brainstem pathways?
Cerebellum
Basal Ganglia
Cerebellum - In charge of what?
Controls pining and the patterns of muscles activated with eye movements, head movements, limb movements, body movements
Basal Ganglia - In charge of what?
Selection and initiation of specific motor programs
Cortical Motor Areas
Project to brainstem and spinal cord.
Important for skilled movement
Brainstem
Important for posture, eye movements, eating, breathing, “that kind of thing”
What are the clinical consequences of the combined hierarchical and parallel organization of the motor pathways?
Alternate pathways for producing movement.
After a stroke, there are some back-up pathways that can contribute to partial functional recovery.
Three Primary Cortical Motor Pathways
Lateral Corticospinal Tract
Ventral Corticospinal Tract
Corticobulbar Tract
Lateral Corticospinal Tract
Major component of the lateral pathway
Skilled limb movements
Ventral Corticospinal Tract
Major component of the medial pathway
Axial muscle control (the 10% of the fibers in the pyramids that don’t cross)
Corticobulbar Tract
Brainstem equivalent of Lateral & Ventral Corticospinal Tracts
Controls primarily cranial nuclei, facial muscles, jaw muscles, and muscles for swallowing & speaking
Four Brainstem Motor Pathways
Rubrospinal Tract
Tectospinal Tract
Reticulospinal Tract
Vestibulospinal Tract
Rubrospinal Tract
Minor component of the Lateral Descending Pathway
Originates from Red Nucleus, involved in limb control
Tectospinal Tract
Medial Descending Pathway
Originates from Superior Colliculus
Head-eye coordination during gaze
Reticulospinal Tract
Medial Descending Pathway
Automatic movements and posture
Vestibulospinal Tracts
Medial Descending Pathway
For posture and balance
Areas in which lobe are the primary source of descending cortical pathways?
Frontal Lobe
From which cortical layer (and in which areas) do the three primary cortical motor pathways arise?
Projection Neurons (Layer V + a little bit of IV) in the following areas:
Primary Motor Cortex
Premotor Cortex
Supplementary Motor Cortex/Area (SMA, SMA medial surface)
Cingulate Motor Area (CMA, medial surface)
Primary Motor Cortex
Brodmann’s Area 4
Precentral Gyrus
Execution of Movements
Lesions in the Primary Motor Cortex produce
Weakness
Paralysis
Incoordination
Premotor Region
Brodmann’s Area 6
Contains Supplementary motor Area (SMA)
Planning of complex sequences of movements involving coordination of both limbs, especially the distal extremity
Where within Brodmann’s Area 6 (Premotor Region) is the Supplementary Motor Area (SMA) located?
Dorsomedial
Where within Brodmann’s Area 6 (Premotor Region) is the Premotor Cortex located?
Lateral
Premotor Cortex
The lateral portion of the Premotor Region (Brodmann’s Area 6)
Receives input from the “Where” pathways of both vision and auditory systems
Directs limb movements to targets of interest (reaching for thangs)
Cingulate Motor Area (CMA)
Brodmann’s Area 31
Within cingulate sulcus and on cingulate gyrus
Receives input from areas involved in cognitive and emotional functions
May participate in emotionally-driven motor behaviors
Where do projections from the Primary Motor Cortex descend?
Through the Genu and Posterior Limb of the Internal Capsule
Where do projections from the SMA, CMA and Premotor Cortex descend?
Through the Anterior Limb of the Internal Capsule
Which is more important? Projections from the Primary Motor Cortex, or projections from the SMA, CMA and Premotor Cortex?
Primary Motor Cortex!
Damage to the Genu and Posterior Limb of the Internal Capsule can produce paralysis. Damage to the Anterior Limb does not!
Internal Capsule - From Genu through Posterior Limb, what is the somatotopic organization of descending motor fibers?
Face (Genu)
Arm
Trunk
Leg
After the decussation of the pyramids, where are 90% of the descending motor fibers? This refers to the 90% that crossed over.
In the Lateral Pathways (the lateral column of the white matter in the spinal cord)
What’s contained in the lateral column of the white matter of the spinal cord?
Lateral Corticospinal Tract
Rubrospinal Tract
Which lateral descending systems go to the limbs, especially the hands and the feet?
Lateral Corticospinal Tract
Rubrospinal Tract
Where do the Lateral Corticospinal Tract and the Rubrospinal tract project within the spinal cord?
Lateral Column on the ventral horn
Lateral aspects of the intermediate layer interneurons
After the decussation of the pyramids, where are 10% of the descending motor fibers? This refers to the 10% that did not cross over.
They stay in the midline
In the Medial Pathway (the Ventral Corticospinal Tract)
Where do Medial Descending Tract fibers project?
Medial Motor Neurons
Interneurons in the medial part of the intermediate zone
Most important: BILATERAL projections!!!!
Which medial descending systems go to the axial and girdle musculature?
Ventral Corticospinal Tract
Where does the Lateral Corticospinal Tract originate?
Brodmann's Area 4 (Primary Motor) Brodmann's Area 6 (Premotor Cortex) Brodmann's Area 3 (Somatosensory) Brodmann's Area 1 (Somatosensory) Brodmann's Area 2 (Somatosensory)
Lateral Descending Pathways
Lateral Corticospinal Tract
Rubrospinal Tract
Where does the Lateral Corticospinal Tract decussate?
At the motor decussation (Spinal Cord)
Where does the Rubrospinal Tract originate?
Magnocellular (caudal) part of the Red Nucleus
Where does the Rubrospinal Tract Decussate?
Red Nucleus (right at the start!!) Decussation occurs at the Ventral Tegmental Area of the Midbrain
Caudal part of the Red Nucleus
Magnocellular Part
Gives rise to the Rubrospinal Tract
Medial Descending Pathways
Ventral Corticospinal Tract
Vestibulospinal Tract
Reticulospinal Tract
Where does the Ventral Corticospinal Tract decussate?
Spinal Cord
Purpose of Vestibulospinal and Reticulospinal Tracts
Automatic movements, some specific eye movements
Lateral Pathways - Summary
Lateral Corticospinal Tract
Rubrospinal Tract
Limb motor neurons - Lateral ventral horn
Descending control - Lateral column of white matter
Crossed - Have consequences on movement by contralateral side of the body.
Lesions (even small ones) have profound effects
Medial Pathways - Summary
Ventral Corticospinal Tract
Lateral Vestibulospinal Tract
Axial and proximal motor neurons - Medial Ventral Horn
Descending control - Medial Ventral column of white matter
Bilateral
Lesions have a less severe effect
Corticospinal Tract - Origins
Originates from Arm, Trunk. Leg
Corticobulbar Tract - Origins
Originates from Facial Area
Corticobulbar Tract
Cranial Nerve Equivalent of Corticospinal Tract
Descending projections from the cortex (Face)
Genu of Internal Capsule
Cranial Nerve Nuclei of Pons and Rostral Medulla
These are the nuclei innervate striated muscle (except extraocular motor nuclei) - V, VII, Nucleus Ambiguus (projects to IX, X, XI), XI, XII
Nucleus Ambiguus
Projects to Cranial Nerves IX, X, XI
Corticobulbar System - Bilateral Control
Jaw (V) Larynx, Pharynx (Nucleus Ambiguus: IX, X, XI) Tongue (XII) Upper Facial Muscles (VII) This control is bilateral and redundant
Corticobulbar System - Contralateral Control
Lower Facial Muscles (VII)
What do you see in a stroke affecting the Corticobulbar System?
No change to upper face, but lower face weakness/paralysis on the contralateral side
Cortex to Trigeminal Motor Nucleus Path
Internal Capsule
Basis Pedunculi
Corticobulbar Portions of the Pons
Bilateral Projections to Trigeminal Motor Nucleus
What is the most common cause of lesions in the posterior limb of the internal capsule?
Thrombosis or hemorrhage:
Anterior Choroidal Artery
Middle Cerebral Artery (above the level of the anterior commissure)
What provides the blood supply for the Genu of the Internal Capsule?
Internal Carotid Artery
Branch of Heubner (off the ACA)
Capsular infarcts commonly lead to
Total Hemiparesis (including lower face)
Why is the upper face spared during a capsular infarct?
Redundancy!
Upper facial motor neurons are somewhat bilateral. They also receive strong projections from other areas besides the Primary Motor Cortex (The Cingulate Motor Area, for example). These other areas typically descend in the anterior limb (unaffected by most internal capsule strokes).
Typical internal capsule stroke affects which parts?
Genu & Posterior Limb
Ventral Anterior / Ventral Lateral Nuclear Complex
Thalamic Motor Nuclei
Receives projections from both cerebellum and basal ganglion
Projects to Premotor and Primary Motor Cortex
From which structures does the Ventral Anterior / Ventral Lateral Nuclear Complex (Thalamic Motor Nuclei) receive its input?
Cerebellum
Basal Ganglia
Where does the Ventral Anterior / Ventral Lateral Nuclear Complex (Thalamic Motor Nuclei) project out to?
Premotor Cortex
Primary Motor Cortex
Basal Ganglion projects to
Ventral Anterior Nuclear Complex
Cerebellum projects to
Ventral Lateral Nuclear Complex
In the Basis Pedunculi, where do the fibers from the Genu and Posterior Limb of the Internal Capsule travel?
Middle 1/3
Medial-to-Lateral, what order do we see the fibers within the basis pedunculi?
Face
Arm
Trunk
Limb
Where does the Tectospinal Tract originate?
Superior Colliculus
What does the Tectospinal Tract control?
Movement of the head and the eyes with conjugated gays
Course of the Facial Motor Nucleus & Nerve
Fibers run dorsal and medial, then at the Genu, curve around and on top of the Abducens Nucleus at the area forming the Facial Colliculus
Facial Colliculus
The bump on the anterior wall of the 4th Ventricle caused by the Genu Facial Nerve curving around and over the Abducens Nucleus.
Input to Facial Motor Nucleus
Descending corticobulbar fibers
Bilateral for upper face
Unilateral for lower face
