Exam #6: Postural Control & Locomotion

Question 1

What are the functions of medial system motor pathways?

Answer 1

1) Control of posture & locomotion

2) Control of axial & proximal muscles

Question 2

What is the sensory or afferent limb of the vestibulocollic (vestibulo-cervical)? Does this reflex act at the neck or limbs?

Answer 2

This is the reflex that rights head position WITHOUT visual input

• Input is via the vestibular system
• Output to the cervical spine

Question 3

What is the sensory or afferent limb of the vestibulospinal? Does this reflex act at the neck or limbs?

Answer 3

Lateral vestibulospinal tract originates in the “lateral vestibular nucleus”

• Projects down the length of the spinal cord IPSILATERAL motoneurons
• Stimulation produces EXENTSION

*Causes DECEREBRATE posturing in conjunction with the PONTINE RETICULOSPINAL tract

Question 4

What is the sensory or afferent limb of the cervicocollic? Does this reflex act at the neck or limbs? Does this reflex act at the neck or limbs?

Answer 4

This is another reflex the maintains the vertical position the head

• Input is proprioception from the neck muscle spindles
• Ouput is back to neck musculature

Question 5

What is the sensory or afferent limb of the tonic neck reflexes? Does this reflex act at the neck or limbs?

Answer 5

• Proprioceptors in the neck
• Causes flexion of the legs and extension of the arms with EXTENSION OF THE NECK

*Antagnoist to the tonic neck reflex

Question 6

What is the sensory or afferent limb of the labyrinth righting reflex? Does this reflex act at the neck or limbs?

Answer 6

• Vestibular system
• Causes flexion of the arms and extension of the legs with FLEXION of the neck

*Antagonist to tonic neck reflex

Question 7

What are symmetric tonic neck reflexes? What kind of patient would exhibit these reflexes?

Answer 7

This is normally seen in infants at ~4-6 months & ends at 1 year

• Neck EXTENDED
• Upper limbs EXTEND
• Lower limbs FLEX

**This can be seen in patients with vestibular damage

Question 8

What are asymmetric tonic neck reflexes? What kind of patient would exhibit these reflexes?

Answer 8

This is a primitive reflex normally seen in infants (suppressed at 6 months)

• Turn head
• Limbs on SAME side EXTEND
• Limbs on OPPOSITE side FLEX

**This can be seen in patients with vestibular impairment

Question 9

What are the feed-forward mechanisms for controlling posture?

Answer 9

Feedforward= anticipatory

- Corrective action is applied PRIOR to movement

Question 10

What are the feedback mechanisms for controlling posture?

Answer 10

Feedback= compensatory

- Corrective action is applied AFTER movement

Question 11

Where are stepping pattern generators (SPGs) located?

Answer 11

Spinal cord

Question 12

What do SPGs do?

Answer 12

Stepping reflex i.e. elicit alternating patters of flexion and extension of the knee & hip

Question 13

What was the swinging room experiment?

Answer 13

This was an experiment where test subjects were put in a room where the floor was STATIONARY, and the moved back & forth to observe their postural reflexes

• Walls moved back, subject swayed back
• Walls moved forward, subject swayed forward

Question 14

How was the swinging room experiment related to the role of vision in postural stability?

Answer 14

This experiment demonstrated that postural stability was partly due to visual input

Question 15

Which age group, toddlers or adults was most strongly affected by the visual stimulus in the swinging room experiment?

Answer 15

Toddlers–fell when they tried to stand in the swinging room

Question 16

List sensory systems involved in the control of posture.

Answer 16

1) Vestibular
2) Proprioceptive
3) Cutaneous
4) Visual

**Note that “vection” is the term used to described perception of self-motion induced by visual stimuli

Question 17

Define the term posture . How does posture differ from postural stability?

Answer 17

Posture= orientation of body & limbs in space

Postural stability= balance

Question 18

What are the three behavioral functions of postural adjustments?

Answer 18

1) Support head & neck against gravity/ external forces
2) Keep center of gravity balance over base
3) Stabilize supporting parts of the body during movement of other parts

Question 19

What is decerebrate posturing?

Answer 19

Extension of all 4 limbs & neck

Question 20

What is decorticate posturing?

Answer 20

Extension of legs & flexion of arms

Question 21

What lesions cause decerebrate posturing?

Answer 21

Lesions to the upper pons (below the red nucleus in the midbrain)

Question 22

What lesions cause decorticate posturing?

Answer 22

Lesions in the:

• Internal capsule
• Upper midbrain/ diencephalon

Question 23

Clinically, what causes a switch from decorticate to decerebrate posturing?

Answer 23

Extension of an infarct from involving the upper midbrain to upper pons will cause a switch in posturing type

Question 24

What stretch reflex will occur to maintain posture in an experiment with BACKWARD movement of a platform?

Answer 24

Gastrocnemius

Question 25

What will happen to the gasttrocnemius reflex with repeated backward movement of the platform?

Answer 25

Progressively earlier reflex

Question 26

What happens when the person trained to backward movement of the platform has the platform tilted?

Answer 26

Postural instability–reflex diminishes with time now

Question 27

What two extrapyramidal tracts descend the length of the spinal cord & facilitate motor neurons of extensor muscles?

Answer 27

Lateral vestibulospinal tract

Pontine reticulospinal tract

Question 28

What is the general function of the medial vestibulospinal tract?

Answer 28

Reflex head movement in response to vestibular stimuli

**Note that the tract only goes down to the upper thoracic cord

Question 29

What is the general function of the reticulospinal system?

Answer 29

• Anticipatory postural adjustments

- Activation of locomotoion & controlling speed

Question 30

What is the colliculospinal tract? What is the function of the colliculospinal tract?

Answer 30

• Also called “Tectospinal tract”
• Projects from superior colliculi to cervical spinal cord

*Involved in the control of neck muscles