Motor Control Flashcards
Stellate cells
Receive thalamocortical input.
What are areas with lots of stellate cells called?
Granular cortex
Is the primary cortex more granular or agranular?
Agranular (small layer 4, with a large 5th layer)
Where are stellate cells found?
Layer 4 of the 6 layers
Where are pyramidal cells found?
Layer 5
Pyramidal cells
Neurons that project out of the cortex. Projects out of the brainstem and into the spinal cord.
Betz cells
Really big pyramidal cells, distinguish the motor cortex
Area 4
Primary motor cortex
Area 6
Premotor cortex
Parts of area 8
Visual field
What do the frontal eye fields do?
Gaze control, image stabilization, changing fixation
How do the frontal eye fields work on image stabilization?
Fixation, VOR, optokinetic response
How do the frontal eye fields change fixation?
Saccades, smooth pursuit, vergence, cancellation of VOR
What is the horizontal component of gaze control?
Paramedian pontine reticular formation (PPRF)/ horizontal gaze center
What is the vertical component of gaze control?
Rostral interstitial nucleus of the medial longitundinal fasiculus/ vertical gaze center
Saccades
Ballistic eye movements occur (can’t stop once they start). Can be voluntary or automatic. Need to be bilateral
PPRF projects where?
To the ipsilateral abducens and contralateral CN III (via medial longitudinal fasciculus)
Where do the frontal eye fields project?
To the contralateral PPRF and the vertical gaze center. Does this directly or via the superior colliculus
Frontal eye field injury
- Loss of voluntary saccades to the contralateral side
- Eyes deviate to the side of the lesion
- Can’t move gaze away from stimulus
- Symptoms may resolve over time
Superior colliculus
Important for orienting to a stimulus (via tectospinal tract) for involuntary saccades
Functional organization of primary motor cortex (M1)
- Stimulation usually evokes simple movement of ind. body part (NOT ind. muscle)
- Movement evoked at low stimulus intensity
What is movement being evoked at a low stimulus intensity indicative of?
Large, direct pathway to brainstem and LMNs
Primary motor cortex function
Force, direction, extent, velocity
Premotor cortex inputs
Supplementary motor area
Cingulate motor area
Prefrontal cortex (planning, learning, executive function)
Posterior parietal cortex
Cerebellum and basal ganglia via thalamus
Premotor cortex organization
Dorsal–reaching
Ventral–grasping, cognitive control
Premotor cortex function
Higher level of motor coordination, multijoint motions that are more complex, stereotyped actions, transforming sensory cue into motor actions
Sensorimotor transformations
Transforming sensory cues into motor actions by premotor cortex. Externally driven.
Does the primary motor cortex or the premotor cortex produce a higher level of coordination?
Premotor cortex. Also has more complex, multi-joint actions.
Mirror neuron example
Monkey watches another primate picking up food. Neurons respond as if the monkey was picking up the food himself.
How does the premotor cortex respond in a behavioral context? Coffee cup example
Bigger response when hand reaching in to pick up the full coffee cup. Much slower response when moving to pick up the empty coffee cup.
Premotor cortex lesions
Inability to:
- Respond properly to stimuli
- Plan appropriate movements based on circumstances
- Learn new sensory-motor associations
- Steer arm correctly
Supplementary Motor area functional organization
Evokes motion in multiple joints (fewer than premotor, but more than M1). Involved in posture changes
Supplementary motor inputs
M1, Prefrontal cortex, posterior parietal cortex, basal ganglia and cerebellum
Supplementary motor area function
Internal movement generation (no direct response to external stimulus). Activity linked to: learning sequences of movements, performing learned movements, mental rehearsal.
What happens when tasks become highly proficient (become habits)?
Supplementary motor control decreases and M1 assumes control
Supplementary Motor area lesions
Reduction in internally driven movements
Loss of suppression of motor programs triggered by visual stimuli (alien hand syndrome and utilization behavior)
Neglect of the affected limb
Alien hand syndrome
Contralateral “semi-purposeful” movements that are outside the patient’s volitional control
Utilization behavior
Use of objects in an inappropriate setting (excessive response to stimuli)
Corticobulbar and corticospinal tracts pathway (until they split)
M1, premotor, SMA + somatosensory cortex–>internal capsule–> cerebral peduncle –> pons –>pyramidal tracts on ventral side of medulla
Where does the corticobulbar tract go when it splits from the corticospinal tract?
To the cranial nerve nuclei (CN III, IV, V3, VI, VIII, IX, X, XI, XII)–nuclei with motor components
Corticobubar projections–bilateral, ipsilateral, or contralateral?
Most are bilateral (depends on the target nucleus)
Corticobulbar tract and voluntary facial movements
Lower face: contralateral M1
Upper face: bilateral control (indirect connections through reticular formation)
Emotional facial movements
Controlled by the cingulate
Upper face: bilateral
Lower face: contralateral
What type of lesion does it have to be when the entire side of face is paralyzed?
Lower motor neuron
What happens with an upper motor lesion in the corticobulbar tract?
Facial paralysis on the contralateral lower face.
Corticospinal tract after split from corticobulbar?
Sends collaterals to the red nucleus and the reticular formation. Cont. to medulla and then to spinal cord
Lateral corticospinal tract
Controls lateral parts of body. Innervates distal limbs
Ventral (anterior) corticospinal tract
Primarily innervates axial and proximal limb muscles. Don’t decussate
How many of the corticospinal tract fibers decussate? What type are they?
90%. Lateral corticospinal tract.
Corticospinal tract branches to contact what?
Alpha-motorneurons that contact many muscles or interneurons that connect to alpha-motorneurons
Where are most of the direct contacts with aplha-motorneurons and corticospinal tracts?
In the forearm and hand
What is the benefit of the corticospinal tracts connecting to interneurons?
The can regulate a larger number of muscles and it allows for multi-jointed movement coordination
Rubrospinal tract function and location
Primary motor pathway in lower vertebrates. Control of arms in humans. Will become more active if the corticospinal tract is damaged. Involves red nucleus. Terminal is the upper half of spinal cord
Magnocellular input and output
Input: motor cortex
Output: spinal cord
Parvocellular input and output
Input: cerebellum
Output: inferior olive
Vestibulospinal tract inputs
Vestibular organs and cerebellum
Medial vestibular nucleus termination point and function
Termination: bilaterally in the medial ventral horn. Reg. head position
Lateral vestibular nucleus
Activates physiological extensor muscles when deviations from stable posture detected.
Reticulospinal tract function
Coordinate movements of trunk and proximal limbs
Reticulospinal tract nuclei
Pontine reticular formation
Medullary reticular formation
