Descending Pathways Flashcards
basically 4 parts to the motor system:
1- reflex component (SC); alpha cells “final common pathway” bc all tracts have to go through this pathway; without it, muscles can’t get innervated
2-cerebrum, basal ganglia; have to thing, increase coordination. no direct influence on alpha cells. worth through control centers
3-cerebral cortex: have to think. more about fine, controlled volitional movement
4-brain stem control centers: midbrain, pons, medulla- automatic movements
what are characteristics of the ventral medial descending system?
receives fibers primarily from cortical area 6
bilaterally distributed
located in the ventro-medial portion of the intermediate gray matter
-the intermediate zone contains long and intermediate propriospinal neurons
tracts located in the ventral and ventral lateral funiculus
high degree of collateralization
tracts synapse on long propriospinal interneurons
collateralization=
polysynaptic branches going into many segments - reason why you can’t isolate one of the deep core muscles- core is concerned with stability rather than dexterity
what are the 6 tracts of the ventral medial descending system?
1- lateral vestibulospinal 2-medial vestibulospinal 3-lateral reticulospinal (medullary) 4-medial reticulospinal (pontine) 5-tectospinal 6-olivo spinal
what is the function of the ventral medial descending system?
synergistic activation of large number of muscle elements
primarily works on axial and proximal muscles in maintaining postural movements
stabilizes core musculature-deep back and neck; controls postural muscles
what would happen if there was a lesion in the ventral medial descending system?
postural changes: trunk and limbs; decrease righting reactions; can’t steer axial and proximal movements
very difficult to lose this system bc it is bilateral (R side of the brain controls R and L body; L side of the brain controls both R and L side of the body)
what are characteristics of the lateral descending system?
contralateral representation
primarily receives cortical fibers from area 4
location in gray matter- terminates in lateral and dorsal parts of the intermediate gray- this is the location of short propriospinal interneurons that travel ipsilaterally
located dorsal laterally in medulla and SC’s lateral funiculus
what are the 2 tracts of the lateral descending system?
1- rubrospinal
2-pontospinal (reticular formation’s tract for lateral group)
what is the function for the lateral descending system?
increase fractionalization of movement especially with distal musculature
fractionization= breaking down gross motor movements into discrete movements
what would happen if there was a lesion in the lateral descending system?
distal limb (especially hand) decrease dexterity of fingers and distal musculature
**this system is only contralateral (R brain controls L limb)
what are characteristics of the pyramidal system (volitional)?
originates directly from the cerebral cortex
laterally located in SC
very little collateralization
goes both to ventral medial and lateral systems
similar to lateral system
(corticospinal tract)
isolated in medulla
what are the functions of the pyramidal system?
voluntary control
high degree of fractioniztion of movement
needed in movements that involve learning and selection
tends to facilitate flexions and inhibit extensors (decreases in higher life forms)
modulates sensory input
what are the 3 tracts of the pyramidal system?
1-lateral corticospinal
2-anterior corticospinal
3-tract of Barnes
**1 tract coming down from the brain stem but 3 tracts in the SC
what would happen if there was a lesion in the pyramidal system?
decrease muscle tone decrease cutaneous reflexes slow tendon reflexes decrease initiation & execution of movement (esp digits) weakness fatigability spasticity??
modulatory descending tracts:
??
