Postural control and locomotion Flashcards
Motor neurons innervating axial and proximal muscles are in the medial or lateral part of the anterior horn of the spine?
Medial
Motor neurons innervating distal muscles are in the lateral or medial part of the anterior horn of the spine?
Lateral
What is the function of the lateral corticospinal tract?
Voluntary control of the flexors of the hands and digits
What is the function of the rubrospinal tract?
Recall this is the ape one–flexion of the hands and the digits
What is the function of the ventromedial pathway?
Posture and locomotion via axial extensor muscle excitation
What is the origin, route, and termination of the lateral vestibulospinal tract?
Origin = vestibular nuclei
Route = all spinal cord
Terminates on extensor and flexor muscles of the limbs and girdle
What is the function of the lateral vestibulospinal tract?
provides way for vestibular input to affect posture
What is the origin, route, and termination of the medial vestibulospinal tract?
•origin – vestibular nuclei
•only descends as far as upper thoracic cord
Terminates in the muscles of the head and neck
What is the function of the medial vestibulospinal tract?
•main function is mediation of reflex head movements in response to vestibular stimuli. It helps adjust the position of the head in response to postural changes
What is the origin and route of the medial (pontine) reticulospinal tract?
- origin - pontine reticular formation
* descends to all levels of the spinal cord
What is the function of the medial (pontine) reticulospinal tract?
Facilitate muscle tone of lateral extensors via the gamma motor neuron loop
Summarize the gamma motor neuron loop. (this is in case you have forgotten)
Stimulation of gamma motor neurons produces stretch on muscle spindles. These activate type Ia fibers, which synapse on alpha motor neurons to produce muscle tone
What is the origin and route of the lateral (medullary) reticulospinal tract?
• origin - medullary reticular formation
Terminates at all spinal cord levels
What is the function of the lateral (medullary) reticulospinal tract?
Excites flexors, inhibits extensors
The lateral and medial reticulospinal tracts have opposing functions. Which excites extensors and inhibits flexors?
medial excites extensors, inhibits flexors.
Lateral is opposite
What is the function of the reticulospinal system?
can modulate reflex action during movement
What is the overall function of the reticulospinal tract?
Muscle tone
What is the overall function of the vestibulospinal tract?
Posture and balance
True or false: the reticulospinal tract is heavily influenced by projections from the cortex via cortico reticulo tract
True–integrates vestibular and other sensory input with motor commands from cerebral cortex
What is the origin and route of the the tectospinal tract?
Origin = superior colliculus Route = projects to cervical spinal cord
What is the function of the tectospinal tract?
Reticulospinal tracts important in coordinating head and eye movements
(the “look that way” reflex)
What is the function of the superior and inferior colliculi?
Superior = visual integration and reflexes
Inferior = auditory integration and reflexes
What is posture?
overall position of the body and limbs relative to each other and
orientation of body and limbs in space.
What is postural stability?
“the ability to control the center of mass in relationship to the base of support.”
What is the purpose of postural adjustments? (3)
- Support head
- Maintain center of gravity
- Stabilize supporting parts of the body during movement
What are the two mechanisms that posture can make use of to keep things stable (think proprioceptive things)?
Feedforward and feedback
What system of the body that plays a role in posture senses sway?
Vestibular
What are the four systems of the body that play a role in posture (think romberg)? (4)
- Vision
- Proprioception
- Vestibular
- Cutaneous tactile receptors
What is vection?
The perception of self-motion induced by visual stimuli
What is visual kinesthesis?
Feeling of body movement when large part of a person’s visual field is moving
What are the postural reflexes that maintains the head in an upright position? (3)
- Vestibulocollic (vestibular)
- Cervicocollic (proprioception)
- Visual
What is the asymmetrical tonic neck reflex?
Infants will extend limbs toward the side the head/neck is turned–this is normal until 6 months-ish
Vestibular and neck reflexes can have opposing actions on limb muscles. Why is this desirable?
This is desirable since otherwise voluntary movement of the head would stimulate vestibulospinal reflexes which would change posture every time head was turned or tilted
What is the symmetrical tonic neck reflex?
When the neck is extended the upper limbs extend and the lower limbs flex
When is the symmetrical tonic neck reflex normal or abnormal?
appears in infants around 4-6 months and disappears before 1 year of age
Can appear in cerebral/vestibular damage
Why does the tonic neck reflex present in pts with vestibular damage?
Normally the vestibular postural reflexes (tonic labyrinthine reflex) on the limbs are opposite to those caused by neck proprioceptors. When vestibular reflexes are lost with vestibular damage, the unopposed tonic neck reflexes become visible.
What is the labyrinthine reflex?
When the neck is extended the upper limbs flex and the lower limbs extend (opposite that of the tonic neck reflex)
What is decerebrate posturing?
Extension of all four limbs and the neck
True or false: decerebrate posturing can be intermittent
True
What causes decerebrate posturing?
If there is a lesion below the red nucleus but above the vestibular nuclei, the lateral vestibulospinal tracts increase their facilitation of extensor motor neurons.
What is decorticate posturing?
Arms flexed and legs extended
What causes decorticate posturing?
lesions of the internal capsule that release both vestibulospinal and tonic neck reflexes from cortical control. Can also be caused by lesions in the upper midbrain/diencephalon.
What is produced by turning a pt who has decorticate posturing when you turn their neck?
Asymmetrical tonic neck reflexes in the arms
A lesion in the supratentorial space will produce what: decerebrate or decorticate posturing?
Decorticate
How is postural stability maintained?
Through continuously monitoring posture and making appropriate adjustments
True or false: reflexes are not able to be modified
False
What are the two results of the series of experiments she described in lecture?
- Reflexes are modifiable
2. The body can retrain reflexes if doing so increases postural balance
What is the feedforward control mechanism?
Apply corrective action before there is error in controlled variable
What is the feedback control mechanism of reflexes?
Appropriate correction is applied after error (e.g. loss of balance) is detected
What allows decerebrate cats to regain walking motion?
Stepping pattern generators in the spinal cord
True or false: newborn infants show a stepping reflex?
true
Do humans have stepping pattern generators?
Yes, but does not function as well as in cats
How do stepping pattern generators work?
the actions of both legs are coordinated through commissural fibers and LMNs.
Why doesn’t the stepping pattern generator not work in humans as well as in cats?
Human walking requires cortical control of ankle dorsiflexion and general postural control to maintain balance. Afferent information is used to adjust the timing of the step cycle and to facilitate the transition from stance to swing phase of gait.
What is the MOA of selective dorsal rhizotomy?
Loss of gamma motor neuron loop by eliminating the Ia fibers
Why does cutting the dorsal roots decrease muscle tone in a subject with decerebrate rigidity?
Loss of gamma motor neuron loop by eliminating the Ia fibers
Which type of rigidity is also known as gamma ridigity?
Decerebrate
