Week 4 - Upper Motor Neurons and Cortical Control of Movement Flashcards
what are 3 tasks that must be accomplished by the motor system for proper motor control?
- produce accurately timed commands to many muscle groups
- take into account current position of body and distribution of body mass (postural adjustments)
- take into account and compensate for physical characteristics of body and muscle
how is the motor system organized and segregated?
hierarchially organized and functionally segregated
what are the main motor structures in the CNS, from highest to lowest? what are the highest and lowest levels most concerned with, respectively?
association cortex - complex planning and selection cortical motor areas basal ganglia cerebellum spinal cord - most autonomic behaviors
are the descending motor pathways from cerebral cortex or brainstem to LMN in medial ventral horns unilateral or bilateral? what do they do?
CC: unilateral (via lateral white matter of spinal cord); for distal limb muscles (skilled movements); direct terminations
BS: bilateral (via anterior-medial white matter of spinal cord); for axial and proximal limb muscles (posture and balance); indirect terminations
hwo do the local circuit neurons supplying medial and lateral regions of ventral horn differ?
long distance: medial intermediate gray, to axial and proximal limbs (posture, so 2 interneurons exit at every level, one to each side)
short distance: lateral intermediate gray, to distal limbs (fine movements, so only travel down a little way but give off many interneurons at specific levels)
what are direct/indirect terminations on ventral horn motoneurons regulated by?
developmentally regulated; differences relate to dexterity between species and infants/young children
- terminations aren’t yet made in youth, and gone if UMN injury
- amt of fine control also differs between species
what are the 4 types of indirect descending pathway?
projections to a midbrain or brain stem center, then to spinal cord; for gross movement and posture
- cortico-colliculo-spinal (tecto-spinal)
- cortico-rubro-spinal
- cortico-reticulo-spinal
- cortico-vestibulo-spinal
what are the 2 types of direct descending pathway?
connections from large pyramidal cells in layers III and V to ventral spinal cord
- lateral cortico-spinal
- medial cortico-spinal
what does the vestibulospinal tract do? where do they originate?
changes gain of axial and proximal limb reflexes
- facilitates anti-gravity muscles
- originate in lateral and medial vestibular nuclei
what does the reticulospinal tract do? where does it originate?
changes gain of axial and proximal limb reflexes
- for central pattern generator
- originates in pontine and medullary reticular formation
what does the colliculospinal (tectospinal) tract do? where does it originate?
axial and midline body orientation
-originates in superior colliculus
what does the rubrospinal tract do? where does it originate?
some distal control, mainly arm flexion
-originates in red nucleus
where does most direct cortico-motor innervation derive from?
primary motor cortex (M1)
what kinds of cells control our motor units?
most projections are from giant Betz cells
-Betz are only in motor areas, especially primary motor cortex
where are most motor areas of the cortex found? how many skeletal and ocular motor areas are there?
on lateral and medial surfaces
-over 5 skeletal and over 2 ocular motor areas
what defines a cortical motor area?
- projects to motor neurons in the spinal cord (either direct CM projections or indirect via interneurons
- projects to M1
- contains Betz cells or equivalent large layer V projection neurons
- can be stimulated at low thresholds to produce movements of discrete muscles or muscle groups
- displays changes in activity related to parameters of movement
what are association areas and how do they compare to cortical motor areas?
prefrontal cortex, posterior parietal cortex, temporal cortex, and pre-supplementary motor cortex
-DON’T meet all definitions for a cortical motor area, but can still participate in regulation of motor function
what makes up the premotor cortex?
lateral premotor cortex
- dorsal premotor area
- ventral premotor area
medial premotor cortex
- supplementary motor cortex
- cingulate motor areas
what does a lesion to the lateral corticospinal tract do? (pre-op, post-d1, post-d7)
testing to grab food
pre-op: can grab and pull w/o problem, in 0.3 seconds
post-d1: it takes over 1 second to figure out where food is and pull it out
post-d7: could improve to 0.8 seconds, but still never at level of pre-op
what underlies the recovery of improving reactions in the LCST lesion?
local circuit neurons
what are methods to study motor cortex?
- anatomical staining and tracing
- microelectrode stimulation of small #s of cells
- micro- and macro-electrode recordings
- spike-triggered averaging
- spontaneous - lesions
- non-invasive imaging
what are 2 key features about cortical control of movement?
- individual muscles are represented in multiple locations (even w/in M1)
- individual corticospinal neurons diverge to influence multiple motor neuron pools, thus multiple muscles
what does it mean that “individual muscles are represented in multiple locations”?
- general somatotopy exists, but detailed analysis of motor map shows re-representations of individual muscles
- so outputs from disparate parts of cortical motor areas converge on a common set of motor neurons
what does it mean that “individual corticospinal neurons diverge to influence multiple motor neuron pools, thus multiple muscles”?
muscles are involved in production of same movement (synergists)
-thus, control of spinal cord motor neurons by cortical motor areas displays both convergence and divergence
