6.4 Descending Motor Pathways Flashcards
What does the pre-frontal cortex do?
Makes the cognitive decision to perform a motor task
What does the posterior parietal cortex do?
provides information about the world and the body
Provides sensory guidance
What does the pre-motor/ supplementary motor areas do?
Sequence actions
What does the primary motor cortex do?
execute actions for a motor program
What do the primary somatosensory area and posterior parietal cortex do?
Provide continual updates during the task
What do the caudal, rostral, lateral ad medial areas of M1 do?
Caudal: brings limbs towards body
Rostral: Reaching
Lateral: face becomes involved
Medial: legs
What happens during training of a new task?
The region involved with that task will become larger so will have a larger cortical representation
Where do sensory inputs converge?
Posterior parietal cortex
What do lesions in the PPC cause?
neglect of body or the outside world, body integrity identity disorder
What is the neural activity in the PPC dependent on?
The goal of the activity - highly active when reaching/searching/manipulating an object but otherwise silent for goaless hand gestures
What is the role of the lateral pre-motor cortex?
Prime M1 for motor actions
Coordination of both sides of the body
Code for intention to execute the appropriate motor behaviours in response to an external event
What regions of the lateral PMC are involved in performing and imagining a task?
BA6 and 4 for performing and BA6 only when imagining
What are the rostral/ventral areas of lateral PMC?
Brocas area - speech production
What elicits the SMA?
Thought to be evoked by internal cues (memory)
Where does SMA have its output?
M1
Where do the corticospinal fibres originate?
M1, SMA, PMA, S1
How do the corticospinal fibres descend?
Through the corona radiata, internal capsule, cerebral peduncles, pass through the pons, enter the pyramids on ventral aspect of the medulla
80% decussate to form lateral C/S
10% descend in ipsilateral lateral C/s
10% form the anterior C/S tract
What does the corticospinal tract control?
input to motor neurones that innervate skeletal muscle - especially flexors
What does the crticobulbar tracts control?
The motor nuclei of the cranial nerves
How do the corticobulbar fibres descend?
Originate from cells in the head and face region, descend through corona radiata then medial part of the internal capsula. Enter the cerebral peduncles medial to corticospinal tract, synpase bilaterally onto motor nuclei
Which corticobulbar tract does not have ipsilateral innervation?
Lower facial nucleus
What is the role of the rubrospinal tract?
Provide innervation to the upper limb flexors
Where do fibres for the rubrospinal tract begin and terminate?
Red nucleus and terminate in the Rexed region V-VIII of the cervical spinal cord
What is the role of the reticulospinal tract?
Pontine/medial: activates spinal reflexes of antigravity muscles
Medullary/lateral: Inhibits antigravity muscles
Where do the reticulosponal tracts commence?
Pontine/medial: cells from the pontine reticular formation
Medullary/lateral: from the medullary reticular formation
Where do the reticulosponal tracts finish?
All levels of the spinal cord VII and VIII for pontine and VII and IX for medullary on alpha and gamma motor neurons
What is the role of the tecto-spinal tract?
Orientation reflexes of the head primarily towards visual, auditory and somatosensory information
What is the pathway of the tecto-spinal tract?
Originate in the superior colliculus
Firbres cross the midline in the midbrain and descend in the C/L central medulla
Terminate in the C/L intermediate grey (VI and VII) in cervical levels
What is the role of the vestibulospinal tract?
Control head position and orientation reflexes
- Mainly extensor groups to hep maintain posture and balance
What is the pathway of the vestibulospinal tract?
Originate in the medial and lateral vestibular nuclei of CN VIII
Fibres from medial descend bilaterally in medial longitudinal fasiculus to lower medulla and upper cervical spinal cord
Fibres from lateral project to al levels of the ipsilateral spinal cord
What is the most common site for UMN syndrome?
Internal capsule from stroke
What are the signs of UMN syndrome?
Paralysis or paresis of affected muscles (not wasting)
Increased muscle tone following initial period of flaccid paralysis
Abnormal reflexes`
What are the causes of UMN syndrome?
Loss of descending inputs onto inhibitory neurons
Loss of descending input to reticular formation, resulting in disinhibition of extensor muscle groups and/or gamma motor neurons
What will you have with a lesion above the red nucleus?
Decorticate posturing with flexion of the upper limb due to disruption of the rubrospinal tract and lower body extension due to disruption of the corticosponal tract
What will you have with a lesion below the red nucleus?
Decerebrate posturing with extended neck and elbows, internally rotated feet ad hands
Thought to be due to inappropriate gamma motor neuron activity
What are the signs of LMN damage?
Paralysis and atrophy of affected muscles
Loss of reflexes
Lossof muscle tone
Fasciculations/fibrillations
What will you see with an UMN lesion of the face?
Weakness of inferior facial muscles
What will you see with LMN lesion of the face?
Weakness of superior and inferior muscles of the face
