8.8. Supraspinal regulation of muscle functions. Postural reflexes.

Question 1

I. Supraspinal motor control
1. What are the features of Supraspinal motor control?

Answer 1

• Supraspinal motor control is based in the medulla, midbrain, cerebellum + basal ganglia and the motor cortex
• The movement can be conscious (lateral pathways) or unconscious (medial pathways).

***Pyramidal + extrapyramidal system terminology is not used here.

Question 2

II. Major pathways connecting the brainstem and cortex with the spinal cord
1. What are the 2 Major pathways connecting the brainstem and cortex with the spinal cord?

Answer 2

1. Lateral pathways: in the lateral funiculus of the spinal cord. Control conscious manipulation and movement coordination
2. Medial pathways: in the ventral funiculus of the spinal cord. Deals more with postural reflexes via axial muscles, coordination etc.

Question 3

II. Major pathways connecting the brainstem and cortex with the spinal cord
2. What are the location and function of lateral pathways?

Answer 3

• in the lateral funiculus of the spinal cord.
• Control conscious manipulation and movement coordination

Question 4

II. Major pathways connecting the brainstem and cortex with the spinal cord - lateral pathways
3A. What are the 3 main lateral pathways?

Answer 4

1. Lateral corticospinal tract (80%)
2. Rubrospinal tract
3. Lateral corticobulbar tract

Question 5

II. Major pathways connecting the brainstem and cortex with the spinal cord - lateral pathways
3B. What are the features of Lateral corticospinal tract (80%)?

Answer 5

• pyramidal decussation.
• Can have direct or indirect synapse with an α-motor neuron, unique to humans/chimps

Question 6

II. Major pathways connecting the brainstem and cortex with the spinal cord - lateral pathways
3C. What are the features of Rubrospinal tract?

Answer 6

• From red nucleus to the spinal cord.
• Innervates neck muscles + (some) large arm muscles -> flexor reflexes in upper limb

Question 7

II. Major pathways connecting the brainstem and cortex with the spinal cord - lateral pathways
3D. What are the features of Lateral corticobulbar tract

Answer 7

Lateral corticobulbar tract: innervates lower face + tongue

Question 8

II. Major pathways connecting the brainstem and cortex with the spinal cord
4A. What are the feature and location of medial pathways?

Answer 8

• In the ventral funiculus of the spinal cord.
• Deals more with postural reflexes via axial muscles, coordination etc.

Question 9

II. Major pathways connecting the brainstem and cortex with the spinal cord - medial pathways
5A. What are the 6 main medial pathways?

Answer 9

Question 10

II. Major pathways connecting the brainstem and cortex with the spinal cord - medial pathways
5B. What are the features of anterior corticospinal tract?

Answer 10

• Corticospinal tract (20%)
• Uncrossed.
• Innervates medially located muscles (activatebilaterally)

Question 11

II. Major pathways connecting the brainstem and cortex with the spinal cord - medial pathways
5C. What are the features of Vestibulospinal tract?

Answer 11

• Lateral part gets afferentation from semicircular organs
• medial part gets afferentation from otoliths + SC organs

Question 12

II. Major pathways connecting the brainstem and cortex with the spinal cord - medial pathways
5D. What are the features of Vestibulospinal tract?

Answer 12

mostly excitatory

Question 13

II. Major pathways connecting the brainstem and cortex with the spinal cord - medial pathways
5E. What are the features of Medullary-reticulospinal tract?

Answer 13

mostly inhibitory

Question 14

II. Major pathways connecting the brainstem and cortex with the spinal cord - medial pathways
5F. What are the features of Tectospinal tract?

Answer 14

• From superior colliculus to spinal cord.
• Vision + sound stimulus

Question 15

II. Major pathways connecting the brainstem and cortex with the spinal cord - Reticular and vestibular nuclei in the brainstem
6. What are the main features of Reticular and vestibular nuclei in the brainstem?

Answer 15

• There are several nuclei in the brainstem which can affect the movement of our body
• The brainstem likes to excite motor neurons + interneurons -> get rigidity in the musculature

Question 16

II. Major pathways connecting the brainstem and cortex with the spinal cord - Reticular and vestibular nuclei in the brainstem
7. What are the features of excitatory nuclei?

Answer 16

• Excitatory: vestibular, pontine reticular nuclei
• Excite neck muscles, axial muscles (which maintain
  posture/balance), anti-gravity muscles, eye movements

Question 17

II. Major pathways connecting the brainstem and cortex with the spinal cord - Reticular and vestibular nuclei in the brainstem
8. What are the features of Inhibitory nuclei?

Answer 17

• Inhibitory: cortex, red nucleus, medial reticular formation
• These ‘’higher center’’ like to limit the exaggerated rigidity caused by the brainstem
• If there is no action from the higher centers, the midbrain would like to increase the overall muscle tone

Question 18

III. Postural reflexes
1. What are of Postural reflexes?

Answer 18

Postural reflexes (controlled by the brainstem) are automatic movements that control the equilibration we require once upright and moving with the effects of gravity.

Question 19

III. Postural reflexes
2. What is the role of postural reflex?

Answer 19

• They maintain posture, balance and fluidity of movement

Question 20

III. Postural reflexes
3. What is the localization of postural reflex?

Answer 20

The localization of these postural reflexes can be visualized with decerebration and decortication which is the separation/cutting of the brainstem from the cortex either at the level of ponto- medullary junction or above the red nucleus (these reflexes also occur with brain injury/lesions)

Question 21

IV. Decerebration
1. What are the features of Decerebration?

Answer 21

• red nucleus is not included
• The higher centers (cortex, red nucleus, cerebellum) are not able to reduce the overall excitatory effect of the midbrain -> can see the ↑ rigidity in the body:

Question 22

IV. Decerebration
2. Name of the reflex you can observe in Decerebration?

Answer 22

Tonic labyrinth reflex

Question 23

IV. Decerebration
3. Describe Tonic labyrinth reflex

Answer 23

• red nucleus is not included
• The higher centers (cortex, red nucleus, cerebellum) are not able to reduce the overall excitatory effect of the midbrain -> can see the ↑ rigidity in the body:

Question 24

V. Decortication
1. What are the features of Decortication?

Answer 24

Question 25

V. Decortication 2. What are the reflexes of Decortication?

Answer 25

Question 26

VI. Cerebral cortex 1. What is Motor cortex?

Answer 26

- Motor cortex (precentral gyrus) is the center of voluntary movements, as well as the motivation and planning associated with these movements. - This area also regulates muscle tone and movements that need precise sensory-motor coordination.

Question 27

VI. Cerebral cortex 2. What are subdivisions of motor cortex?

Answer 27

This functional area is divided into: - Primary motor cortex – Brodmann 4 - Premotor cortex + supplementary motor area – Brodmann 6 - Frontal eye movement area – Brodmann area 8

Question 28

VI. Cerebral cortex -Steps in order of motor activity 3A. What are the steps in order of motor activity?

Answer 28

1. Regulates the muscle tone (↓rigidity) 2. Realization, planning, execution of voluntary movements 3. Special movements found in cerebral cortex 4. Cortical postural reflexes 5. Regulation of movements requiring very precise sensory motor coordination

Question 29

VI. Cerebral cortex -Steps in order of motor activity 3B. What happen in step 1: Regulates the muscle tone (↓rigidity)?

Answer 29

- Cortex would like to suppress the midbrain-originated rigidity (vestibular + pontine reticular nuclei) - Extensors inhibited + flexors stimulated

Question 30

VI. Cerebral cortex -Steps in order of motor activity 3C1. What happen in step 2: Realization, planning, execution of voluntary movements?

Answer 30

Question 31

VI. Cerebral cortex -Steps in order of motor activity - step 2: Realization, planning, execution of voluntary movements 3C2. How does activation of functional areas occur?

Answer 31

Association areas (800ms prior to movement) => supplementary motor area (500ms prior) => premotor area (5ms prior) => primary motor cortex activated (0ms)

Question 32

VI. Cerebral cortex -Steps in order of motor activity - step 2: Realization, planning, execution of voluntary movements 3C3. What happen after Activation of premotor cortex?

Answer 32

It will activate descending motor pathways via medial pathways (ant.cs.tract)

Question 33

VI. Cerebral cortex -Steps in order of motor activity - step 2: Realization, planning, execution of voluntary movements 3C4. What happen if we conduct any voluntary movement?

Answer 33

1. body posture stabilized using the medial pathways – anterior corticospinal tract 2. after few ms, the laterally located muscles which contribute to the movement will be activated by the lateral corticospinal tract => execute movement

Question 34

VI. Cerebral cortex - Steps in order of motor activity - step 3: Special movements found in cerebral cortex 3D. What happen in step 3: Special movements found in cerebral cortex?

Answer 34

Some cortical areas are specialized to execute special movements (eye, hand skills, hand rotation etc.)

Question 35

VI. Cerebral cortex - Steps in order of motor activity - step 4. Cortical postural reflexes 3E1. What are the 3 reflexes found in step 4. Cortical postural reflexes?

Answer 35

- Optical righting reflex - Placing reflex - Hopping reflex

Question 36

VI. Cerebral cortex - Steps in order of motor activity - step 4. Cortical postural reflexes 3E2. What is the feature of Optical righting reflex?

Answer 36

According to many different visual sensations, we are able to correct our body position

Question 37

VI. Cerebral cortex - Steps in order of motor activity - step 4. Cortical postural reflexes 3E3. What is the feature of Placing reflex?

Answer 37

Placing reflex: causes the ‘’stepping on stair’’-like movement

Question 38

VI. Cerebral cortex - Steps in order of motor activity - step 4. Cortical postural reflexes 3E4. What is the feature of Hopping reflex?

Answer 38

if we push someone to the side => they will have a jumping-like movement to keep the balance

Question 39

VI. Cerebral cortex -Steps in order of motor activity 3F. What happen in step 5 "Regulation of movements requiring very precise sensory motor coordination"

Answer 39

- We can have colliding information from an object in various situations => example: to touch an object behind a prism (prism changes pictures of the object = difficult to touch) - conflicting information from visual system and different information from proprioceptors from hand - But the cortex should be able to realize how to solve this eventually