6.4 Descending Motor Pathways

Question 1

What does the pre-frontal cortex do?

Answer 1

Makes the cognitive decision to perform a motor task

Question 2

What does the posterior parietal cortex do?

Answer 2

provides information about the world and the body

Provides sensory guidance

Question 3

What does the pre-motor/ supplementary motor areas do?

Answer 3

Sequence actions

Question 4

What does the primary motor cortex do?

Answer 4

execute actions for a motor program

Question 5

What do the primary somatosensory area and posterior parietal cortex do?

Answer 5

Provide continual updates during the task

Question 6

What do the caudal, rostral, lateral ad medial areas of M1 do?

Answer 6

Caudal: brings limbs towards body
Rostral: Reaching
Lateral: face becomes involved
Medial: legs

Question 7

What happens during training of a new task?

Answer 7

The region involved with that task will become larger so will have a larger cortical representation

Question 8

Where do sensory inputs converge?

Answer 8

Posterior parietal cortex

Question 9

What do lesions in the PPC cause?

Answer 9

neglect of body or the outside world, body integrity identity disorder

Question 10

What is the neural activity in the PPC dependent on?

Answer 10

The goal of the activity - highly active when reaching/searching/manipulating an object but otherwise silent for goaless hand gestures

Question 11

What is the role of the lateral pre-motor cortex?

Answer 11

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

Question 12

What regions of the lateral PMC are involved in performing and imagining a task?

Answer 12

BA6 and 4 for performing and BA6 only when imagining

Question 13

What are the rostral/ventral areas of lateral PMC?

Answer 13

Brocas area - speech production

Question 14

What elicits the SMA?

Answer 14

Thought to be evoked by internal cues (memory)

Question 15

Where does SMA have its output?

Answer 15

M1

Question 16

Where do the corticospinal fibres originate?

Answer 16

M1, SMA, PMA, S1

Question 17

How do the corticospinal fibres descend?

Answer 17

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

Question 18

What does the corticospinal tract control?

Answer 18

input to motor neurones that innervate skeletal muscle - especially flexors

Question 19

What does the crticobulbar tracts control?

Answer 19

The motor nuclei of the cranial nerves

Question 20

How do the corticobulbar fibres descend?

Answer 20

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

Question 21

Which corticobulbar tract does not have ipsilateral innervation?

Answer 21

Lower facial nucleus

Question 22

What is the role of the rubrospinal tract?

Answer 22

Provide innervation to the upper limb flexors

Question 23

Where do fibres for the rubrospinal tract begin and terminate?

Answer 23

Red nucleus and terminate in the Rexed region V-VIII of the cervical spinal cord

Question 24

What is the role of the reticulospinal tract?

Answer 24

Pontine/medial: activates spinal reflexes of antigravity muscles

Medullary/lateral: Inhibits antigravity muscles

Question 25

Where do the reticulosponal tracts commence?

Answer 25

Pontine/medial: cells from the pontine reticular formation

Medullary/lateral: from the medullary reticular formation

Question 26

Where do the reticulosponal tracts finish?

Answer 26

All levels of the spinal cord VII and VIII for pontine and VII and IX for medullary on alpha and gamma motor neurons

Question 27

What is the role of the tecto-spinal tract?

Answer 27

Orientation reflexes of the head primarily towards visual, auditory and somatosensory information

Question 28

What is the pathway of the tecto-spinal tract?

Answer 28

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

Question 29

What is the role of the vestibulospinal tract?

Answer 29

Control head position and orientation reflexes

- Mainly extensor groups to hep maintain posture and balance

Question 30

What is the pathway of the vestibulospinal tract?

Answer 30

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

Question 31

What is the most common site for UMN syndrome?

Answer 31

Internal capsule from stroke

Question 32

What are the signs of UMN syndrome?

Answer 32

Paralysis or paresis of affected muscles (not wasting)
Increased muscle tone following initial period of flaccid paralysis
Abnormal reflexes`

Question 33

What are the causes of UMN syndrome?

Answer 33

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

Question 34

What will you have with a lesion above the red nucleus?

Answer 34

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

Question 35

What will you have with a lesion below the red nucleus?

Answer 35

Decerebrate posturing with extended neck and elbows, internally rotated feet ad hands

Thought to be due to inappropriate gamma motor neuron activity

Question 36

What are the signs of LMN damage?

Answer 36

Paralysis and atrophy of affected muscles
Loss of reflexes
Lossof muscle tone
Fasciculations/fibrillations

Question 37

What will you see with an UMN lesion of the face?

Answer 37

Weakness of inferior facial muscles

Question 38

What will you see with LMN lesion of the face?

Answer 38

Weakness of superior and inferior muscles of the face