topic 11: brain control of movement

Question 1

What is the motor control hierarchy?

Answer 1

• high- strategy (goal of the movement ) –> association areas of neocortex, basal ganglia
• middle- tactics (sequence of muscle contractions) –> motor cortex, cerebellum
• low- execution (goal-directed movement and posture) –> brainstem, spinal cord

Question 2

what are the 2 major descending pathways from the brain?

Answer 2

-lateral column
-ventromedial column

Question 3

what is the lateral pathways involved in?

Answer 3

-voluntary movement of distal musculature, under direct cortical control

Question 4

what is the ventromedial pathways involved in?

Answer 4

-control of locomotion, balance, body position and uses visual environment to maintain posture, under brain stem control

Question 5

What are part of the lateral pathways?

Answer 5

-corticospinal tract (aka pyramidal tract)
-rubrospinal tracts

Question 6

where does the corticospinal tract originate?

Answer 6

-areas 4 and 6 of frontal lobe –> aka the motor cortex
-most of the remaining axons derived from somatosensory areas of parietal lobe

Question 7

where does the corticospinal tract travel from its origin?

Answer 7

cortex –> using internal capsule, telencephalon and thalamus –> through base of cerebral peduncle –> traverse pons –> collect and form tract at base of medulla (this tract forms bulges called medullary pyramid), running down the ventral surface of medulla –> at junction of medulla and spinal cord decussates at the pyramidal decussation –>axons collect in lateral column of spinal cord, form lateral corticospinal tract –> axons terminal in dorsolateral region of ventral horns and intermediate gray matter (location of motor neurons and interneurons that control distal muscles, particularly flexors

Question 8

where does the rubrospinal tract originate?

Answer 8

red nucleus in the midbrain

Question 9

where does the rubrospinal tract go from its origin?

Answer 9

red nucleus –> decussate at pons (almost immediately) –> move down spinal cord parallel to corticospinal tract

Question 10

what are the ventromedial pathways?

Answer 10

-vestibulospinal tract
-tectospinal tract
-pontine reticulospinal tract
-medullary reticulospinal tract

Question 11

where does the vestibulospinal tract originate? and where does it relay information to?

Answer 11

-origin is in the vestibuli nuclei of the medulla
-relay sensory information from vestibular labyrinth in the inner ear

Question 12

where does the vestibulospinal tract project down to?

Answer 12

-projects bilaterally down the spinal cord and activated the cervical spinal circuit that control neck and back muscle and thus guide head movement
-also projects ipsilaterally down to lumbar spinal cord –> help maintain upright and balanced posture by facilitating extensor motor neurons of legs

Question 13

where does the tectospinal tract originate? and what does this part of brain receive input from? and what does this part of that brain with that information?

Answer 13

-superior colliculus of the midbrain
-superior colliculus receives input from retina, projections from visual cortex, afferent axons carrying somatosensory and auditory information
-from these input, superior colliculus constructs map of world around us

Question 14

where does the tectospinal tract go after the colliculus?

Answer 14

-after leaving colliculus, tectospinal tract quickly decussate and project close to midline into cervical regions of spinal cord –> help control muscles of neck, upper trunk and shoulders

Question 15

where do both the reticulospinal tracts arise from?

Answer 15

mainly the reticular formation of brainstem –> control by motor cortex

Question 16

what is the pontine reticulospinal tract role?

Answer 16

-enhances the antigravity reflexes of spinal cord, facilitating extensors of lower limps, standing posture

Question 17

what is the role of the medullary reticulospinal tract?

Answer 17

-opposite of pontine reticulospinal tract role –> liberates the antigravity muscles from reflex control

Question 18

what is the motor cortex?

Answer 18

-part of frontal lobe, area 4 and 6
-area 4 lies anterior to the central sulcus on precentral gyrus and area 6 lies just anterior to area 4
-area 4 known as the primary motor cortex, M1
-area 6 lateral region called premotor area (PMA) and the medial region called supplementary motor area (SMA) –> perform similar functions but on different groups of muscles
-SMA sends axons that innervate distal motor units directly, PMA connect primarily with reticulospinal neurons that innervate proximal motor units

Question 19

describe the effect of corticospinal lesions

Answer 19

-Deficit in fractionated movement of arms and hands
-Recovery if rubrospinal tract is intact
-Subsequent rubrospinal lesion reverses recovery
-Strokes in human: motor cortex or corticospinal tract
–->Paralysis on contralateral side
–-> Some recovery over time

Question 20

Describe the corticocortical projections to M1 (area 4)

Answer 20

-Direct projections to primary motor cortex (area 4) come from somatosensory areas 3a, 1, 2 and somatic sensory association areas of parietal lobe (5 and 7)

-3a is receiving area for muscle proprioceptor sensation

-Many cells in areas 2 and 5 respond to joint receptors

-Area 3b is cutaneous sensation – has no projection to MI

-Premotor Area (area 6) projects heavily to primary motor cortex

Question 21

Describe the cortical projections to PMA (areas 6 and 8)

Answer 21

-PMA (area 6) receives sensory information about state of body from parietal somatosensory association areas 5 and 7
-PMA selects between manipulation movements

-Premotor Area 8 receives visuospatial information from visual association areas
-selects for orientation type of movements

Question 22

describe the contributions from the posterior parietal cortex (areas 5 and 7) in terms of movement

Answer 22

-Contains body image and information about position in space

-Depends on somatosensory, proprioceptive and visual inputs

-Area 5 from area 3, 1, 2 (somatic sensory cortex)

-Area 7 from higher order visual areas of cortex (e.g. area MT)

Question 23

Describe the function of cerebellum in movement

Answer 23

-sequence of muscle contractions

-Cerebellum receives input from regions of cerebral cortex that plan and initiate skilled movements

-Also receives information from sensory systems that monitor course of movements
-Computes a “motor error” from these inputs
-Corrects output of motor cortex via its thalamic connections
-Corrections occur in real time, but also over longer periods, as in motor learning e.g. resetting gain of vestibulo-ocular reflex

Question 24

describe cerebellar lesion in terms of movement

Answer 24

–Ataxia; uncoordinated and inaccurate movements
–Dyssynergia; decomposition of synergistic multi-joint movements
–Dysmetria; overshoot or undershoot target