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Neuroscience Block 3 > Supraspinal Motor Control > Flashcards

Supraspinal Motor Control Flashcards

0
Q

What is the difference between UMN and motor control coming from the cerebellum or basal ganglia?

A

UMN are just upstream of motor neurons in the ventral gray. Cerebellar and basal ganglia neurons do not make direct connections with local motor neuron pools.

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1
Q

What controls the local motor circuits in the ventral horn of the spinal cord and brainstem motor nuclei?

A

Upper motor neurons descending from higher cortical centers or networks in the brainstem

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2
Q

What are the two major divisions of the descending motor pathways?

A
  1. Medial- controls proximal and axial muscles and remain uncrossed or are bilateral
  2. Lateral- control distal limb muscles (fine movement)
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3
Q

Which descending pathway is phylogenetically older?

A

The medial pathway.

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4
Q

Do the medial descending pathways cross or remain uncrossed?

What do they control?

A

They either stay uncrossed or innervate bilaterally.

  1. Control axial (trunk) antigravity muscles
  2. Extensor motor groups for axial and proximal muscles
  3. Control posture and balance
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5
Q

What are the medial descending tracts?

A
  1. Vestibulospinal
  2. Descending MLF
  3. Reticulospinal
  4. Ventral corticospinal
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6
Q

Do the lateral descending tracts cross or remain uncrossed?

What do they control?

A

They cross and control:

  1. Flexors
  2. More distal muscles
  3. Fine motor control
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7
Q

What are the lateral descending tracts?

A
  1. Lateral corticospinal tract
  2. Rubrospinal tract
  3. Tectospinal
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8
Q

What are the motor components of the cerebral cortex and what are their Brodmann #s?

A
  1. Primary motor cortex- Brodmann 4 just in front of central sulcus
  2. Promoter Cortex- Brodmann 6
  3. Supplementary motor cortex - Brodmann 8
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9
Q

What is meant by ascending hierarchy of motor execution?

A
  1. Simple movements just use primary motor cortex (one finger)
  2. Patterned movement uses primary and premotor cortex (several fingers)
  3. Complex movements activate all three (sequences of fingers and arm movements)
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10
Q

Where does mental rehearsal of movements take place?

A

Premotor cortex and supplementary motor cortex

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11
Q

What way do motor commands progress?

A

Supplementary -> premotor -> primary

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12
Q

On the somatic map, how are limbs arranged from medial to lateral?

A

Legs, trunk, arms, face

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13
Q

On a homunculus for primary motor cortex, what parts will be exaggerated?

A

Parts involving fine motor control like lips, hands, tongue

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14
Q

What is the activity of a cortical neuron most correlated with when assessed using Microelectrode stimulation: a specific muscle or a specific action?

A

New data associates stimulation of a cortical motor neuron with a specific motor task involving multiple muscles

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15
Q

Neuronal activity in the motor cortex depend on what two things?

A
  1. Motor task (not individual muscles)

2. Direction of the movement (where the movement ends, not starts)

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16
Q

What is directional tuning of neuronal activity in the motor cortex?

A

Microstimulation of the same cortical neuron with the same intensity will cause movement from any start point to Go to the same endpoint (goal-directed movement)

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17
Q

What is spike-triggered averaging?

What does it show?

A

Technique to discern components of the EMG driven by specific cortical neurons.

  1. Stimulate a cortical neuron and record the single motor neuron spike
  2. Measure the activity of the muscle and use a rectifier to make the negative stimuli positive (flexor/extensor)
  3. Trigger averager input
  4. Spike-triggered averaging

It shows that more than one muscle is correlated with a single neuron spike

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18
Q

What does it mean that motion is goal-directed?

A

Stimulation elicits movement to the same end-point regardless of the start point

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19
Q

Where do corticospinal and corticobulbar projections originate?

A

In betz cells in layer five of the primary motor cortex and primary sensory cortex. (layer five projects to subcortical layers)

20
Q

What percent of corticospinal fibers originate in primary sensory cortex?
What do these fibers modulate?

A

30-40% and they modulate sensorimotor function within the spinal cord.

21
Q

Through what tracts do areas of the cortex responsible for motor planning and execution send their fibers?
(directly and indirectly)

A

Directly through the corticospinal tract and indirectly though the reticular formation and red nucleus.

22
Q

Where do the majority of corticospinal tract fibers decussate?
What tract do the decussates fibers travel in?
The fibers that don’t cross travel in what tract?

A

At the level of the pyramids in the medulla (most caudal end of the medulla)
Decussate-> lateral corticospinal tract end contralateral to the cerebral cortex
Uncrossed -> ventral corticospinal tract to end bilaterally in the cord

23
Q

What is innervated by the fibers of the lateral corticospinal tract?

A

Flexors
Distal muscles
Fine motor control

24
Q

Lesions in the cerebral cortex will have what effect on motor activity?

A

Large effect on the execution of fine motor skills because you are ruining the lateral corticospinal tract.
Smaller effect on motor strength and proximal muscles because they have other inputs

25
Q

What do projections from the ventral corticospinal tract innervate?

A

Motor neurons in the medial Ventral horn that regulate axial and proximal limbs for posture, stability and balance

26
Q

What is the path from cortex to spinal cord for the corticospinal tract?

A

Cerebral areas-> internal capsule-> cerebral peduncle-> pontine fiber bundles-> pyramids-> ventral ipsilateral or decussates to travel in the contralateral lateral corticospinal tract

27
Q

Do The fibers from the primary sensory cortex that travel in the corticospinal tract travel with the medial or lateral motor fibers more frequently? Why?

A

Sensory fibers generally travel with lateral (crossed fibers) for modulation

28
Q

Where does the Vestibulospinal tract originate and descend?

What do the neurons synapse with?

A

In the lateral vestibular nucleus and descends ipsilaterally through the brainstem and Ventromedial spinal cord

The neurons synapse with alpha motor neuron pools

29
Q

What is the purpose of the Vestibulospinal pathway?

A

Provides information about head movement (from the canals and otoliths) to the spinal motor system to maintain posture and balance

30
Q

What descending pathway originates in the medial vestibular nucleus?
Where does it project?
What does it control?

A

The MLF

Projects to the cervical and thoracic cord bilaterally to control head movements

31
Q

Where does the reticulospinal tract originate?

A

In the pontine and medullary reticular formation

32
Q

What tract originates in the pontine reticular formation?

What is the function of this tract?

A

Medial reticulospinal tract excites extensor gamma motoneurons

33
Q

What pathway originates in the medullary reticular formation?
What does it control?

A

The lateral reticulospinal pathway inhibits extensor gamma motoneurons

34
Q

Where does the pontine reticular formation receive excitatory input from?
Where does the medullary reticular formation receive excitatory input from?

A

Pontine from the ascending spinoreticular path and cortical input

Medullary from the cerebral cortex

35
Q

Where does the rubrospinal tract originate and how does it descend?
What does it innervate?

A

It starts in the red nucleus, crosses in the midbrain, projects to the contralateral cervical spinal cord levels.

It excites flexor motoneurons of the upper extremity

36
Q

Which neurons in the red nucleus are used in lower mammals (humans use corticospinal instead) ?
Which neurons of the red nucleus do humans mostly use?

A
  1. Magnocellular

2. Parvocellular which project to inferior olive then cerebellum for feedback

37
Q

Where does the tectospinal tract originate?
How does it descend?
What does it synapse on?
What is its function?

A

Deep layers of the superior colliculus, cross in midbrain, descend in contralateral tract.
Projects to medial motoneuron pools bilaterally in the cervical region for head and trunk positioning with visual stimuli to the superior colliculus

38
Q

What symptoms are associated with LMN loss?

A
  1. Focal weakness
  2. Decreased tone
  3. Decreased reflex
  4. Focal Atrophy
  5. Fasciculation
39
Q

What symptoms are associated with UMN deficits?

A
  1. Weakness
  2. Very poor fine motor control
  3. Enhanced tone (enhanced resistance to movement around a joint)
  4. Enhanced reflex
  5. Toes curl up on babinski
40
Q

What happens to fine motor control with a LMN lesion?

A

Not much. UMN deficiencies will markedly diminish them but LMN doesnt do too much

41
Q

What happens to muscle strength with an UMN deficit?

A

It is maintained. LMN deficits will diminish strength

42
Q

What factors determine spasticity in UMN deficits?

A
  1. Hyper-reflexia (enhanced response and spread to other muscle groups)
  2. Increased muscle tone (resistance to movement around a joint)
  3. Extended toes in babinski test
43
Q

Where would a lesion be in decerebrate posturing?

What would be seen in patients?

A

Mid-colliculus transection.

Increased tone in proximal extensors

44
Q

Why do you see increased tone in proximal extensors in a decerebrate lesion?

A

The reticulospinal and Vestibulospinal pathways are active but the rubrospinal and corticospinal pathways are disrupted.

Pontine reticular formation excitation of extensors is favored over medullary inhibition.

45
Q

What happens to the elbows and arms in decerebrate posturing?

A

Elbows extend and arms pronate (turn in)

Wrists and fingers flex

46
Q

Where is the lesion where decorticating posturing occurs?

A

Below the red nucleus and rubrospinal pathway so they are sparedb

47
Q

What do you see with elbow and arm in decorticate posturing?

A

Elbow flexing and arm supination (turn out)

Neuroscience Block 3 (20 decks)

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