3.18.14 34 Motor Systems II (Non-cortical fibers and system controls)

Question 1

Name the TRACTS that are considered tonic systems (favor primarily extensors)

Answer 1

Pontine reticulospinal
Vestibulospinal
Tectospinal

Question 2

Name the TRACTS that are considered phasic systems (favor primarily flexors)

Answer 2

Medullary reticulospinal
Corticospinal
Rubrospinal

Question 3

Pontine reticulospinal is tonic or phasic? Medullary reticulospinal?

Answer 3

Pontine = tonic
Medullary = phasic

Question 4

Do the reticulospinal systems (pontine and medullary) terminate ipsilaterally, contralaterally, or bilaterally? Again, which is phasic??

Answer 4

Bilaterally, with stronger effects ipsilaterally

Medullary is phasic (flexors), Pontine is tonic (extensors)

Question 5

Does the vestibulospinal tract terminate ipsilaterally, contralaterally, or bilaterally?

Answer 5

Ipsilaterally

Question 6

Does the rubrospinal tract terminate ipsilaterally, contralaterally, or bilaterally?

Answer 6

Contralaterally

Question 7

Which tract terminates exclusively on alpha motoneurons (not gamma or interneurons) ONLY in cervical and upper thoracic levels?

Answer 7

Rubrospinal tract

Question 8

Rubrospinal tract is considered tonic or phasic?

Answer 8

Phasic

Question 9

Vestibulospinal tract is considered tonic or phasic?

Answer 9

Tonic

Question 10

Tectospinal tract is considered tonic or phasic?

Answer 10

Tonic

Question 11

Medullary reticulospinal tract is considered tonic or phasic?

Answer 11

Phasic

Question 12

Pontine reticulospinal tract is considered tonic or phasic?

Answer 12

Tonic

Question 13

Does the tectospinal tract terminate ipsilaterally, contralaterally, or bilaterally?

Answer 13

Contralaterally

Question 14

Which tract originates in the superior colliculus and pretectum, controlling eye-head and head-neck movements?

Answer 14

Tectospinal tract

Question 15

The cortex sends what three fiber types to control (inhibit/excite) motor systems?

Answer 15

Corticospinal
Corticorubral
Corticobulbar

Question 16

The vestibulospinal tract excites/inhibits…

Answer 16

Excites extensors

Question 17

The rubrospinal tract excites/inhibits…

Answer 17

Excites flexors

Inhibits extensors

Question 18

The lateral CST excites/inhibts…

Answer 18

Excites flexors, primarily

also some extensors and inhibits/excites sensory fibers

Question 19

The anterior CST excites/inhibits…

Answer 19

Excites OR inhibits extensors

Question 20

The pontine reticulospinal tract excites/inhibits…

Answer 20

Excites extensors

Question 21

The medullary reticulospinal tract excites/inhibits…

Answer 21

Inhibits flexors AND extensors

Question 22

The tectospinal tract excites/inhibits…

Answer 22

Excites extensors (upper cervical segments)

Question 23

All tonic systems excite/inhibit…

Answer 23

Excite extensors

Question 24

How does the cortex control the red nucleus? What are the effects (excitation/inhibition)? How does this affect the relevant tract/system?

Answer 24

Corticorubral fibers
Inhibit red nucleus
Inhibits rubrospinal tract (phasic)
--> inhibition excitation of flexors
--> inhibition of inhibition of extensors

Question 25

What do corticobulbar fibers excite/inhibit?

Answer 25

Excite cranial nerves and the medullary reticulospinal system (excites inhibition of flexors and extensors)
Inhibit pontine reticulospinal tract (inhibits excitation of extensors)

Question 26

How does the cortex control the vestibulospinal system? What affect does this have?

Answer 26

It doesn’t…

This leads to tonic excitation of extensors

Question 27

Describe the decorticate condition (physical features)

Answer 27

Arms flexed, legs extended

Question 28

Why are arms flexed in the decorticate condition (1 system)?

Answer 28

The rubrospinal tract is no longer inhibited –> uninhibited flexion of upper limbs (rubrospinal tract does not continue to the legs; only upper thoracic and cervical levels)

Question 29

Why are legs extended in the decorticate condition (3 systems)?

Answer 29

1. The pontine reticulospinal tract is no longer inhibited –> uninhibited extension of the legs
2. The medullary reticulospinal tract is no longer excited –> loss of inhibition of extensors/flexors
3. The vestibulospinal tract remains unaffected –> continued excitation of extensors

Question 30

In general, the cortex INHIBITS excitatory systems of the spinal cord. Provide example(s) of motor system(s) under this form of cortical control.

Answer 30

Pontine reticulospinal system (excites extensors)
Red nucleus (excites flexors)

Question 31

In general, the cortex EXCITES inhibitory systems of the spinal cord. Provide example(s) of motor system(s) under this form of cortical control.

Answer 31

Medullary reticulospinal system (inhibits flexors/extensors)

Question 32

What is the main difference between decortical and decerebrate conditions?

Answer 32

Decerebrate will have extension of both upper and lower limbs, whereas decorticate will have flexion of upper limbs, extension of lower limbs

Question 33

Describe the flaccid condition

Answer 33

This is the immediate shock of a spinal transection; interruption of all descending tracts
It is characterized by areflexia and lack of tone
After shock wears off –> typical UMN syndrome (hyperactive reflexes, increased deep tendon reflexes)