Motor Systems Flashcards
(21 cards)
Motor control is generally hierarchical with multiple looped subsystems. Describe its arrangement.
- Motor planning and coordination
- basal ganglia
- cerebellum
- motor association areas - Descending pathways
- corticospinal
- corticobulbar
- bulbospinal - Local neural networks
- central pattern generators - Lower motor neuron
- aka alpha motor neuron
Where is the primary motor cortex?
Area 4, precentral gyrus
The motor association areas of the cortex are in area 6, including the premotor cortex (PMC) and the supplemental motor cortex (SMA aka MII). Where are these located?
PMC = rostral to primary motor on LATERAL hemisphere
-slide 4-6
SMA = rostral to primary motor on MEDIAL hemisphere
When speaking of somatotopic organization in the ventral (anterior) horn white matter, where are axial, girdle and distal limb musculature located?
Axial = most medial Girdle = intermediate Distal limb = most lateral -flexors more dorsal -extensors more ventral
A basic approach to motor system organization is to separate it into medial and lateral tracks. Describe the function associated with each.
LATERAL
-distal limb and fine motor control
MEDIAL
-girdle and trunk (axial), gross movements like posture and walking
In the lateral system (corticospinal tract, aka pyramidal tract), where will low threshold stimulation produce isolated joint movements.
The precentral gyrus.
Where does the corticalspinal tract of the lateral system originate?
Primary motor (area 4): 50% Supplementary motor (area 6) and premotor (area 6) and somatosensory cortex (area 3,1,2): 50% -slide 9
Approximately 90% of fibers in each pyramid cross where?
The pyramidal decussation in the caudal medulla.
The lateral corticospinal tract is the portion that contributes to the ___ system. Where does it terminate and what is its function?
Lateral.
Terminates in the lateral ventral horn.
Function
- fine motor control of distal muscles
- facilitates motor neuron pools
- deliberate, isolated fractioned movements
- only in tracts that innervate hands and feet
Where does the rubrospinal (red nucleus) terminate? What does it innervate?
On the contralateral lateral anterior horn in hand regions.
-innervates UE flexors
What is different about the anterior corticospinal tract of the medial system vs the lateral system? What muscle do they control?
8% of fibers, they do not cross in the pyramidal decussation; descend ipsilaterally and most terminate at the level where they cross.
CONTROL
-axial and girdle muscles
Distal musculature is primarily controlled by the ___ system.
Lateral (corticospinal), not many redundant systems.
What systems innervate the trunk and girdle?
Directly through anterior corticospinal and indirectly through several cortico-spinal/bulbospinal tracts of the medial system. Predominance of contralateral stimulation. Some redundancy.
What is the primary motor cortex most responsible for?
Deliberate, fractioned and isolated movements.
What is the supplemental motor cortex responsible for?
Patterns of movement involving multiple segments.
Active mental rehersal, assembling routines.
What is the premotor cortex responsible for?
Movement in response to external stimuli.
Reaching and grasping with visual guidance.
T/F: Lower motor neuron lesion always refers to alpha motor neuron in spinal cord.
True.
What does the plantar response (Babinski sign) indicate?
Corticospinal lesion.
Normal response when lateral foot stroked upwards then across metatarsals = flexion of toes
Extension = positive sign
What does a bulbar sign refer to?
Any clinical sign related to brainstem function, particularly cranial nerves.
With MCA cortical stroke, contralateral side is usually most affected, specifically distal limbs > trunk. What gross movement patterns are present?
UE flexion dominated and LE extension.
Loss of fractioned movement.
What is decorticate rigidity?
Remove cortex (rubrospinal tract intact) -ext LE, fxn UE
