Exam #2: Motor Systems II Flashcards
What is the corticotectal tract?
Fibers that originate from the visual association cortex & descend into the tectum of the midbrian
Where do the corticotectal fibers terminate?
- Oculomotor Accessory Nuclei located near the oculomotor
- Superior Colliculus
Where do the axons of the oculomotor accessory nuclei project? What is their function?
To the nuclei of CN III, IV, & VI–producing reflex movement of the eyes
*****Occurs via the Medial Lemniscus
What is the general function of superior colliculus?
Reflex center of the midbrain for visual stimuli
What is the tectospinal tract?
These are projects from the superior colliculus in the midbrain to the spinal cord
What is the function of the tectospinal tract?
These projections from the superior colliculus produce reflex movements of the head & trunk in the direction of a startling stimulus
What is the pyramidal system?
This system consists of two tracts:
1) Corticonuclear tract (terminate in cranial nerves)
2) Corticospinal tract (terminate in spinal cord)
- Lateral corticospinal tract
- Anterior corticospinal tract
What is the function of the pyramidal system?
Conscious voluntary control of movement
What tracts are involved in the involuntary control of motor activity?
1) Reticulospinal
2) Vestibulospinal
**This is the system that coordinates subconscious/ background muscle tone, posture, & balance
What is the antiquated term for the system that maintains background muscle tone, posture, & balance?
Extra-pyramidal
What is the general function of the 1) Reticulospinal and
2) Vestibulospinal tracts?
Generation of subconscious muscle activity that modulates:
1) Muscle tone
2) Posture
3) Balance
*The pyramidal system superimposes its voluntary movement on this system; these systems work together
Outline the corticorubral tract
Corticorubral tract terminates in the red nucleus of the midbrain
*****Note that these axons can become intermingled with the corticospinal tract as they descend into the red nucleus of the midbrain
Outline the rubrospinal tract.
Arises from the red nucleus of the midbrain and descends into the spinal tract
What is the function of the corticorubral tract/ rubrospinal tract?
Stimulation of the extensor muscles of the upper limb i.e. hand and digit
**More important in lower primates but in humans, clinically fairly insignificant
Outline is corticoreticular tract. What are the reticulospinral tracts?
Arises from the cortex & descends via the carona radiata/ internal capsule into the reticular formation
- Reticulospinal tracts are the axons that descend from the reticular formation into the spinal cord
Where do the reticulospinal tract fibers terminate in the spinal cord? What is their function
Gamma motor neurons that synapse with the intrafusal fibers of the gamma loop
- Function in maintaining MUSCLE TONE
- *****Note that there are two divisions of the reticulospinal tract:
1) Medial (Pontine) reticulospinal tract (RST)
2) Lateral (Medullary) reticulospinal tract (RST)
What is the function of the Medial (Pontine) RST?
Stimulation of the paravertebral muscles & limb extensors
*****Thus, Medial Pontine RST= STANDING
What is the function of the Lateral (Medullary) RST?
Inhibition of paravertebral & limb extensor muscles
*****Thus, opposite of Medial Pontine RST: LYING DOWN
What are the two vestibulospinal tracts?
Generally, these tracts run from the vestibular nuclei of the pons to the spinal cord. There are two tracts:
1) Lateral VST
2) Medial VST
What is the function of the Lateral VST?
Stimulation of the paravertebral & proximal limb extensors
I.e. this has the SAME function as the Medial (Pontine) RST–STANDING
What is the function of the Medial VST?
This is a short tract that is involved in maintain the erect posture of the head
What CNS structure is central to maintaining balance? What is the pathway?
Cerebellum
**Cerebellum–>Thalamus–> Motor cortex
Draw the spinal cord and label the location of the different descending motor pathways.
N/A Figure 5-9
What is the function of the anteromedial group of descending motor pathways?
Gross movement of axial & proximal limb musculature to maintain balance
What is the function of the lateral group of descending motor tracts?
Voluntary control of distal muscles in the hands i.e. controlling precise movements of the fingers
What is Brown-Sequard Syndrome?
This is a constellation of symptoms that occurs following hemisection (half) of the spinal cord
What are the manifestations of Brown-Sequard Syndrome?
1) UMN lesion signs ipsilateral
2) LMN lesion signs ipsilateral
3) Loss of reflex activity ipsilateral at the level of the lesion
4) Loss of fine touch ipsilateral
5) Loss of pain & temperature CONTRALATERAL
What is poliomyelitis? What part of the spinal cord is affected?
Viral destruction of neural tissue, specifically the cells of the ventral horn
What is Combined Systems Disease?
B12 def leading to damage of heavily myelinated axons located:
- DC/ML
- Lateral corticospinal tract
Describe the arterial supply to the spinal cord.
Posterior 1/3= posterior spinal arteries (DC/ML)
Anterior 2/3= anterior spinal artery
What part of the spinal cord is most susceptible to interruption of blood flow?
Cervical b/c there is less anastamosis with the radicular arteries
What are the radicular arteries?
Blood vessels that supply the nerve roots of the spinal nerves
**Also, note that the radicular arteries anastaomse with the anterior & posterior spinal arteries
