Exam #2: Motor Systems I Flashcards
What are the different parts of the nervous system that orchestrate motor function?
Motor cortex Thalamus Basal Ganglia Cerebellum Brain stem Spinal Cord
Outline the general pathway that controls voluntary movement.
1) Association cortex– desire
2) Premotor cortical areas–plan
3) Primary motor cortex–execution
What is the function of the motor cortex?
Planning & executing complex voluntary movement
What are the cortical areas involved in motor activity?
1) Primary motor cortex
2) Premotor cortical areas (previously called secondary motor cortex)
What are the two main tracts that are involved in pathways of conscious, voluntary motor control?
1) Corticonuclear tract
2) Corticospinal tract
Where does the corticonuclear tract terminate?
Most cranial nerve motor nuclei
Where does the corticospinal tract terminate?
All spinal levels
What side of the body does the corticospinal tract control?
Contralateral
What cortical areas involved in the production of movement are located in the frontal lobe? What areas are located in the parietal lobe?
Frontal Lobe
- Primary Motor Cortex
- Premotor Cortical Areas
Parietal Lobe
- Posterior Parietal Cortex
What is the general function of the premotor cortical areas? Where are the premotor cortical areas located?
- Frontal lobe
- Planning of movement
What is the function of the primary motor cortex? Where is the primary motor cortex located?
- Frontal lobe (pre-central gyrus)
- Receives the plan from the premotor cortical areas and executes the movement
*Note that this area is also referred to as Brodmann’s area 4
What is the supplementary motor area (SMA)?What is the premotor cortex (PMC)? What is their function?
These are BOTH part of the premotor cortical areas that plan movement
- Specifically, they orient the trunk & proximal limb musculature in the direction of intended movement
What Brodmann area does the SMA & PMC correspond to?
Brodmann 6
What is the Frontal Eye Field (FEF)?
Contains neurons that send axons down to the cranial motor nerve nuclei in the brainstem that are involved in eye movement
Brodmann 8
What is the Posterior Parietal Cortex (PMA)? What is the function?
This is a region in the posterior parietal cortex that is involved in visual guidance of movement
How does the orientation of the motor homunculus compare to the sensory homunculus?
Same medial to lateral organization
- Lower leg & foot medial
- Hand & face distal
What parts of the body have the most cortex dedicated to it?
Face & hand
What area does the Precentral gyrus correspond to? What bout the Postcentral gyrus?
- Precentral gyrus (primary motor cortex)= Bordmann 4
- Postcentral gyrus (primary sensory cortex) = Brodmann 3, 1, & 2
What are the areas of the brain that influence movement?
Somatosensory cortex
Where does the postcentral gyrus synapse to influence movement?
Neurons of the sensory pathways
What layer of the cortex are the upper motor neurons located in?
Layer V
*These are pyramidal cells
What is the difference between an upper and lower motor neuron?
Lower= nerve that innervates a skeletal muscle Upper= nerves that synapse prior to the nerve that projects to skeletal muscle
Outline the corticospinal tract.
1) Cortex Layer 5
2) Corona Radiata
3) Internal capsule
4) Midbrain–Crus Cerebri
5) Basal pons
6) Medulla–Pyramid
7) Spinal cord
Where does crossing over of the corticospinal tract occur?
Caudal Medulla
*****Note, ~85% of the nerves decussate to form the lateral corticospinal tract; those that don’t become the anterior corticospinal tract
Where do the anteror corticospinal tract axons cross-over?
At the level of their innervation in the spine
What do most of the UMN in the spinal cord syapse with?
Interneurons that then synapse with LMN
*Some synapse directly with LMN
What are the crossing fibers called in the medulla?
Motor decussation (in the caudal medulla)
Where does the anterior corticospinal tract decussate? What else decussates here?
Anterior white commissure
*****Note that the spinothalamic tract also decussates here
What is the difference between the Anterior & lateral corticospinal tracts?
Lateral= all level Anterior= C1- T6 only
Where do ALL corticospinal tract neurons synapse?
Contralateral voluntary movement
What muscles does the anterior corticospinal tract control?
Axial muscles of the shoulder and trunk
What does the lateral corticospinal tract control?
Upper limb and lower limb muscles
Review how the morphology of the spinal cord changes with ascending & descending tracts.
Ascending= get thicker as you go up
Descending= get smaller as you go down
What are the signs of an upper motor neuron lesion?
1) Spastic paralysis
2) Hyperreflexia
3) Mild muscle atrophy
4) Babinski’s Sign
Describe the progression of spastic paralysis.
- Temporary paresis, flaccid paralysis, hypotonia, & hyporeflexia
- Regain proximal function after roughly 2x weeks
- Hypotonia converts to Hypertonicity
**Inhibitor reflexes from basal ganglia are blocked, causing hypertonia (uninhibited gamma fibers)
What is the Babinski Reflex?
Fanning & dorsiflexion of the great toe is caused by:
Called the extensor plantar response
- Normal in the newborn b/c descending motor axons are NOT myelinated
What are the signs of lower motor neuron lesion?
1) Decrease in muscle strength
2) Hypotonia
3) Hyporeflexia
4) Flaccid paralysis
5) Severe muscle atrophy
6) Fibrillations (1 fiber)
7) Fasiculations (gross muscle twitch)
What will a lesion of the ACA cause?
Sensory & motor deficits of the contralateral leg/foot
What will a lesion of the MCA cause?
Sensory & motor deficits in the contralateral trunk/UL/ face
What will occlusion of the lenticulostriate arteries effect?
Lenticulostriate= deep branches of the MCA to the internal capsule that will effect:
- DC-ML (VPL thalamus)
- Spinothalamic (Intralaminar)
- Corticospinal tract
**Lesion will cause contralateral motor & sensory deficits
What part of the brain is supplied by the PCA?
Midbrain, specifically in the basis pedunculi/ crus cerebri
What artery supplies the corticospinal tract in the pons?
Basilar/pontine arteries
What does the anterior spinal artery supply
- Anterior corticospinal tract
- Lateral corticospinal tract
- Spinothalamic tracts
What does the posterior spinal artery supply?
DC/ML
