Exam #2: Motor Systems II

Question 1

What is the corticotectal tract?

Answer 1

Fibers that originate from the visual association cortex & descend into the tectum of the midbrian

Question 2

Where do the corticotectal fibers terminate?

Answer 2

• Oculomotor Accessory Nuclei located near the oculomotor

- Superior Colliculus

Question 3

Where do the axons of the oculomotor accessory nuclei project? What is their function?

Answer 3

To the nuclei of CN III, IV, & VI–producing reflex movement of the eyes

*****Occurs via the Medial Lemniscus

Question 4

What is the general function of superior colliculus?

Answer 4

Reflex center of the midbrain for visual stimuli

Question 5

What is the tectospinal tract?

Answer 5

These are projects from the superior colliculus in the midbrain to the spinal cord

Question 6

What is the function of the tectospinal tract?

Answer 6

These projections from the superior colliculus produce reflex movements of the head & trunk in the direction of a startling stimulus

Question 7

What is the pyramidal system?

Answer 7

This system consists of two tracts:

1) Corticonuclear tract (terminate in cranial nerves)
2) Corticospinal tract (terminate in spinal cord)
- Lateral corticospinal tract
- Anterior corticospinal tract

Question 8

What is the function of the pyramidal system?

Answer 8

Conscious voluntary control of movement

Question 9

What tracts are involved in the involuntary control of motor activity?

Answer 9

1) Reticulospinal
2) Vestibulospinal

**This is the system that coordinates subconscious/ background muscle tone, posture, & balance

Question 10

What is the antiquated term for the system that maintains background muscle tone, posture, & balance?

Answer 10

Extra-pyramidal

Question 11

What is the general function of the 1) Reticulospinal and

2) Vestibulospinal tracts?

Answer 11

Generation of subconscious muscle activity that modulates:

1) Muscle tone
2) Posture
3) Balance

*The pyramidal system superimposes its voluntary movement on this system; these systems work together

Question 12

Outline the corticorubral tract

Answer 12

Corticorubral tract terminates in the red nucleus of the midbrain

*****Note that these axons can become intermingled with the corticospinal tract as they descend into the red nucleus of the midbrain

Question 13

Outline the rubrospinal tract.

Answer 13

Arises from the red nucleus of the midbrain and descends into the spinal tract

Question 14

What is the function of the corticorubral tract/ rubrospinal tract?

Answer 14

Stimulation of the extensor muscles of the upper limb i.e. hand and digit

**More important in lower primates but in humans, clinically fairly insignificant

Question 15

Outline is corticoreticular tract. What are the reticulospinral tracts?

Answer 15

Arises from the cortex & descends via the carona radiata/ internal capsule into the reticular formation
- Reticulospinal tracts are the axons that descend from the reticular formation into the spinal cord

Question 16

Where do the reticulospinal tract fibers terminate in the spinal cord? What is their function

Answer 16

Gamma motor neurons that synapse with the intrafusal fibers of the gamma loop
- Function in maintaining MUSCLE TONE

• *****Note that there are two divisions of the reticulospinal tract:
  1) Medial (Pontine) reticulospinal tract (RST)
  2) Lateral (Medullary) reticulospinal tract (RST)

Question 17

What is the function of the Medial (Pontine) RST?

Answer 17

Stimulation of the paravertebral muscles & limb extensors

*****Thus, Medial Pontine RST= STANDING

Question 18

What is the function of the Lateral (Medullary) RST?

Answer 18

Inhibition of paravertebral & limb extensor muscles

*****Thus, opposite of Medial Pontine RST: LYING DOWN

Question 19

What are the two vestibulospinal tracts?

Answer 19

Generally, these tracts run from the vestibular nuclei of the pons to the spinal cord. There are two tracts:

1) Lateral VST
2) Medial VST

Question 20

What is the function of the Lateral VST?

Answer 20

Stimulation of the paravertebral & proximal limb extensors

I.e. this has the SAME function as the Medial (Pontine) RST–STANDING

Question 21

What is the function of the Medial VST?

Answer 21

This is a short tract that is involved in maintain the erect posture of the head

Question 22

What CNS structure is central to maintaining balance? What is the pathway?

Answer 22

Cerebellum

**Cerebellum–>Thalamus–> Motor cortex

Question 23

Draw the spinal cord and label the location of the different descending motor pathways.

Answer 23

N/A Figure 5-9

Question 24

What is the function of the anteromedial group of descending motor pathways?

Answer 24

Gross movement of axial & proximal limb musculature to maintain balance

Question 25

What is the function of the lateral group of descending motor tracts?

Answer 25

Voluntary control of distal muscles in the hands i.e. controlling precise movements of the fingers

Question 26

What is Brown-Sequard Syndrome?

Answer 26

This is a constellation of symptoms that occurs following hemisection (half) of the spinal cord

Question 27

What are the manifestations of Brown-Sequard Syndrome?

Answer 27

1) UMN lesion signs ipsilateral
2) LMN lesion signs ipsilateral
3) Loss of reflex activity ipsilateral at the level of the lesion
4) Loss of fine touch ipsilateral
5) Loss of pain & temperature CONTRALATERAL

Question 28

What is poliomyelitis? What part of the spinal cord is affected?

Answer 28

Viral destruction of neural tissue, specifically the cells of the ventral horn

Question 29

What is Combined Systems Disease?

Answer 29

B12 def leading to damage of heavily myelinated axons located:

• DC/ML
• Lateral corticospinal tract

Question 30

Describe the arterial supply to the spinal cord.

Answer 30

Posterior 1/3= posterior spinal arteries (DC/ML)

Anterior 2/3= anterior spinal artery

Question 31

What part of the spinal cord is most susceptible to interruption of blood flow?

Answer 31

Cervical b/c there is less anastamosis with the radicular arteries

Question 32

What are the radicular arteries?

Answer 32

Blood vessels that supply the nerve roots of the spinal nerves

**Also, note that the radicular arteries anastaomse with the anterior & posterior spinal arteries