Motor Cortex Flashcards
What are some characteristics of stellate cell?
Receive cortico information
Granular cortex is a bunch of these
A lot around sensory tissue
Look like sand in stain
What is motor cortex?
Anatomically: 6 layers, 4 cells, two types, stellate cells in the 4th layer, pyramidal cells everywhere else. Small layer 4 big layer 5
Physiologically:
Where are pyramidal cells projecting in layers 5 and 6?
Subcortically
What are Betz cells?
Large pyramidal cells
In the 5th layer
Only in layer 5
What is area 4?
Motor cortex
What is area 6?
Premotor cortex and supplementary motor cortex
Where is the frontal eye fields?
In front of area 8
What does the frontal eye fields do?
Gaze:
VOR
Fixation
Optokinetic response
Saccades
Smooth pursuit
Vengeance
Cancellation of VOR
Where is the horizontal gaze center?
Paramedian pontine reticular formation
PPRF
Where is the vertical gaze center?
Rostral interstitial nucleus of the medial longitudinal fasciculus
What does the PPRF project to?
Ipsilateral abducens
Contralateral CN III (via MLF)
What do the frontal eye fields do?
Select visual targets
Initiate Saccades and smooth pursuit
Where does the frontal eye field project?
The PPRF directly
And through the superior colliculus
Where is the PPRF?
The pons
What is the path of selecting eye targets?
Frontal eye field –> superior colliculus –> contralateral PPRF –>
What controls the rightward movement?
The left frontal eye field and the right PPRF
What happens when you get injury to the FEF?
Loss of voluntary Saccades to the contralateral side
Loss ability to move gaze away from a stimulus. Stuck involuntarily
Deviation of eyes to the side of the lesion
What are the three cortical motor areas?
SMA
Primary motor cortex
Premotor cortex
What does stimulus of an area of the motor cortex do?
Stimulates movement of a body part not a muscle
What does the M1 region do?
Direction, force among others
What are the inputs to M1?
- Proprioception info: mostly contralateral via dorsal column and VP nucleus of the thalamus.
- Tactile information from the hands
- other cortical area: S1, premotor, cingulate, parietal lobe
- cerebellum and basal ganglion
How is the premotor cortex functionally organized?
Dorsal - reaching
Ventral - grasping, cognitive control
Where does the premotor cortex receive input?
SMA Cingulate motor area Prefrontal cortex (planning and learning) Posterior parietal Cerebellum and basal ganglion
What does the premotor cortex do?
Gives complex multi joint movement
Eating
Sensorimotor transformation: transforming sensory cues into motor actions - externally driven
Way before the action, mirror neurons
What are mirror neurons?
Responds if the monkey were doing an action but the monkey is actually just watching someone do something
Signals intent
Learning by watching
Behavioral context - why we are doing what we do
What happens if there is a lesion in the premotor cortex?
Inability to properly respond to stimuli, plan movements based on circumstances, learn new sensory-motor associations, steer arm directly
What is the functional organization of the SMA?
Homunculus (leg, arm, face caudal to rostral)
What does SMA stimulation do?
Movement in multiple joints
More than M1 but less than premotor
Postural changes
Where does the SMA receive input?
M1
Prefrontal cortex
Posterior parietal cortex
Basal ganglion and cerebellum
What is the function of the SMA?
Internal generation of movement
Activity is linked to learning sequences of movements, performing them, mental rehearsal
Piano playing learning
Suppresses premotor planning when inappropriate
What happens when a movement becomes a habit?
SMA becomes less and the M1 assumes control
What happens when there is a lesion in the SMA?
- Cannot learn new complex sequences
- loss internal drive for movements
- loss of suppression of motor programs triggered by visual stimuli: alien hand syndrome, utilization behavior
- neglect of affected limb
What is alien hand syndrome?
Lesion in the SMA
Contralateral semi-purposeful movements that are outside the patients volitional control
What is utilization behavior?
Caused by a lesion in the SMA
Use of objects in an inappropriate setting
When is premotor and SMA active?
Premotor: when visual cue without prior learning, responds to external
SMA: when there is prior learning, responds to internal
Premotor is not active when the sequence has been learned
SMA is not active when a sequence has not been learned
What are the paths of the corticospinal and corticobulbar tracts?
M1, premotor, SMA, somatosensory –> internal capsule –> cerebral peduncle (base of midbrain)
–> through the pons –> pyramidal tracts on the ventral side of the medulla
Where does the corticobulbar tract projects and how?
Motor cranial nerves
Mostly bilateral
What is normal facial expressions controlled by?
Corticobulbar
What controls emotional facial expression?
The cingulate
What is the voluntary control of facial expression?
Contralateral of lower face
Bilateral of low face
Where does the corticospinal tract project?
Collateral to red nucleus and reticular formation
What is the function of the 10% of the corticospinal tract fibers that do not decussate?
Ventral corticospinal tract (medial)
Collateral sac cross the midline
Primarily innervates axial and proximal limb muscles (medial)
What does the corticospinal tract contact?
- Alpha-motor neurons
- Interneurons that are connected to alpha-motor neurons allowing for coordination
Where is most of the direct contact of the corticospinal tract and the alpha-motor neurons?
Forearm and hand areas
What is the rubrospinal tract associated with?
The red nucleus?
Where is the red nucleus?
The upper midbrain
By the superior colliculi
What are the two components of the red nucleus?
- Magnocellular
- Parvocellular
What is the input and output of the magnocellular part of the red nucleus?
Input: motor cortex
Output: spinal cord
What is the input and output of the Parvocellular part of the red nucleus?
Input: cerebellum
Output: inferior olive
Where does the axons of the red nucleus decussate?
Almost immediately
What is the function of the rubrospinal tract?
Primary motor pathway in lower vertebrates
Terminates in upper half of spinal cord (cervical or thoracic)
Controls arms
Where does the vestibulospinal tract receive input?
The cerebellum and vestibular organs
What is the function of the medial VN and where does it terminate?
Regulates head position
Terminates bilaterally in the medial ventral horn of the spinal cord
What is the function of the lateral VN?
Activates physiological extensor muscles that work against gravity with deviations from posture
What are the two nuclei of the reticulospinal “nuclei”?
Pontine and medullary (rostral and caudal)
Coordinate movements of the trunk and proximal limbs
Really just continuous formation with little organization
What measures your intended output and readjusts?
Cerebellum
How is posture maintained?
By primary physiological extensors
Through the tonic activity of alpha-motor neurons
How do you increase alpha-motorneuron activity thereby tone?
Directly - corticospinal neuron, vestibulospinal, reticulospinal (descending tracts) (gamma as well)
Indirectly - stretch receptors (gamma motor activity) reflex.
How are adjustments are made on the fly?
Feedforward - anticipate, includes reticulospinal
Feedback - includes vistibulospinal tract (random)
What does the vestibulospinal tract contact?
Alpha and gamma motorneurons
What do the vestibulocollic and vestibulospinal reflexes do respectively?
- act on neck muscles to adjust the head
- adjust limb
What are the three things that help you maintain balance?
Vision, proprioception, and the vestibular system
What provides central control of posture?
The corticospinal, rubrospinal, and reticulospinal tracts
Adjust reflex sensitivity
Enable Feedforward adjustments for self-generated movements (planning)
What allows for Feedforward (anticipatory) adjustments?
The corticoreticular and reticulospinal tracts