Exam #6: Review Flashcards
What are the functional differences between nuclear bag and nuclear chain fibers? What types of nerve fibers are associated with these two structures?
Nuclear Bag
- Ia
- Velocity of length change (dynamic)
Nuclear Chain
- II
- Change in length (static)
Why do UMN lesions result in hypertonia?
- Loss of presynaptic inhibition of muscle spindle afferents (from UMN lesion)
- Allows the slow and/or sustained muscle stretch reflex to elicit continual muscle contraction
In the vestibular system, what is the result of stereocilia movement toward the kinocilium? What about away?
Toward= depolarization Away= hyperpolarization
What are the two most common etiologies of positional vertigo?
1) Trauma
2) Viral Labyrinthitis
What are the central connections of the vestibular labyrinth?
- Flocculonodular lobe of the cerebellum
- Vestibular nuclei
What are the four projections of the vestibular nuclei?
1) MLF to EOM (vestibulo-ocular reflexes)
2) Lateral vestibulospinal tract
3) Medial vestibulospinal tract
4) Higher centers
What two pathways are implicated in decerebrate posturing?
Lateral vestibulospinal tract
Pontine reticulospinal tract
**Both facilitate the motor neurons of the extensor muscles
What is the difference between the lateral & medial vestibulospinal tracts?
- Medial descends only to the throacic spinal cord & mediates reflex head movements in response to vestibular stimuli
- Lateral descends the length of the spinal cord & facilitates extension
What is the function of the reticulospinal system?
- Anticipatory postural adjustments
- Activating locomotion and controlling its speed
What is the function of the colliculospinal tract? What is the alternate name for this tract? Where does is project from/ to?
- Also called the “Tectospinal tract”
- Superior colliculus–>cervical spine
- Reflex head movements in response to visual stimuli
What is the vestibulocollic reflex?
Head righting reflex in response to vestibular input i.e. in the absence of visual input
What is the cervicocollic reflex?
Head righting reflex in response to proprioceptive inputs from the cervical spine
Describe the position of a patient with an asymmetric neck reflex?
- Arm & leg of one half of body extended
- Arm & leg of opposite half flexed
- Head rotated toward extended side
What are the specific boundaries of a lesion that will cause decerebrate posturing?
- Below the red nucleus (caudal)
- Above the lateral vestibular nucleus (rostral)
Generally, this is the upper pons/ lower midbrain
What is the major landmark used to describe the lesion that causes decorticate posturing?
Supratenorial i.e. above the tenorium cerebelli
What is gamma rigidity?
- Gamma motor neuron excitation
- Contraction of intrafusal fibers
- Stimulation of Ia afferents
- Contraction of muscle via alpha motor neurons
What is the treatment for severe CP?
Dorsal Rhizotomy i.e. selectively cutting some of the Ia fibers (dorsal lumbar nerves) to damped down excessive gamma rigidity that is part of the CP pathology
What is the Bordmann area for the motor cortex? Premotor cortex? Supplementary motor cortex? Frontal eye fields?
Motor= 4
Premotor= 6
Supplementary= 6
Frontal Eye Fields= 8
What is the function of the premotor area? What would a lesion to the premotor area cause?
Planning related to external stimuli/ visually guided stimuli e.g. reaching & grasping
- The ability to perform such tasks would be diminished
What is the function of the supplementary motor area? What would a lesion to the supplementary motor area cause?
Function: planning in regards to:
1) Internal acts
2) Sequential actions
3) Coordinating both sides of the body
4) Anticipatory adjustments
- Defects in the above abilities AND difficulty initiating/ suppressing movements
Where would a vascular lesion be to involve the premotor cortex vs. the supplementary motor cortex?
ACA= supplementary MCA= premotor
What are the ipsilateral consequences of Brown-Sequard Syndrome?
1) Anesthesia at the level of hemisection
2) Monoplegia
3) Babinski sign
4) Deficits in the DC/ML pathway i.e. vibration, proprioception, touch
What is the contralateral consequence of Brown-Sequard Syndrome?
Spinothalamic pathway damage= deficit in pain & temperature
Draw the functional divisions of the cerebellum. Labal the deep cerebellar nuclei associated with each functional region. Label the UMN or LMN projection of each functional division.
N/A
