Exam #6: Postural Control & Locomotion Flashcards
What are the functions of medial system motor pathways?
1) Control of posture & locomotion
2) Control of axial & proximal muscles
What is the sensory or afferent limb of the vestibulocollic (vestibulo-cervical)? Does this reflex act at the neck or limbs?
This is the reflex that rights head position WITHOUT visual input
- Input is via the vestibular system
- Output to the cervical spine
What is the sensory or afferent limb of the vestibulospinal? Does this reflex act at the neck or limbs?
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
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?
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
What is the sensory or afferent limb of the tonic neck reflexes? Does this reflex act at the neck or limbs?
- 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
What is the sensory or afferent limb of the labyrinth righting reflex? Does this reflex act at the neck or limbs?
- Vestibular system
- Causes flexion of the arms and extension of the legs with FLEXION of the neck
*Antagonist to tonic neck reflex
What are symmetric tonic neck reflexes? What kind of patient would exhibit these reflexes?
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
What are asymmetric tonic neck reflexes? What kind of patient would exhibit these reflexes?
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
What are the feed-forward mechanisms for controlling posture?
Feedforward= anticipatory
- Corrective action is applied PRIOR to movement
What are the feedback mechanisms for controlling posture?
Feedback= compensatory
- Corrective action is applied AFTER movement
Where are stepping pattern generators (SPGs) located?
Spinal cord
What do SPGs do?
Stepping reflex i.e. elicit alternating patters of flexion and extension of the knee & hip
What was the swinging room experiment?
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
How was the swinging room experiment related to the role of vision in postural stability?
This experiment demonstrated that postural stability was partly due to visual input
Which age group, toddlers or adults was most strongly affected by the visual stimulus in the swinging room experiment?
Toddlers–fell when they tried to stand in the swinging room
List sensory systems involved in the control of posture.
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
Define the term posture . How does posture differ from postural stability?
Posture= orientation of body & limbs in space
Postural stability= balance
What are the three behavioral functions of postural adjustments?
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
What is decerebrate posturing?
Extension of all 4 limbs & neck
What is decorticate posturing?
Extension of legs & flexion of arms
What lesions cause decerebrate posturing?
Lesions to the upper pons (below the red nucleus in the midbrain)
What lesions cause decorticate posturing?
Lesions in the:
- Internal capsule
- Upper midbrain/ diencephalon
Clinically, what causes a switch from decorticate to decerebrate posturing?
Extension of an infarct from involving the upper midbrain to upper pons will cause a switch in posturing type
What stretch reflex will occur to maintain posture in an experiment with BACKWARD movement of a platform?
Gastrocnemius
What will happen to the gasttrocnemius reflex with repeated backward movement of the platform?
Progressively earlier reflex
What happens when the person trained to backward movement of the platform has the platform tilted?
Postural instability–reflex diminishes with time now
What two extrapyramidal tracts descend the length of the spinal cord & facilitate motor neurons of extensor muscles?
Lateral vestibulospinal tract
Pontine reticulospinal tract
What is the general function of the medial vestibulospinal tract?
Reflex head movement in response to vestibular stimuli
**Note that the tract only goes down to the upper thoracic cord
What is the general function of the reticulospinal system?
- Anticipatory postural adjustments
- Activation of locomotoion & controlling speed
What is the colliculospinal tract? What is the function of the colliculospinal tract?
- Also called “Tectospinal tract”
- Projects from superior colliculi to cervical spinal cord
*Involved in the control of neck muscles
