lecture 20: somatosensation and motor control Flashcards
forebrain: initiating movement
lashley: perform skilled movements too quickly to rely on feedback about movements so they must be preformed as motor seqeuences with next sequence held in readiness
motor sequence
movement module preprogrammed by brain and prdocued as a unit
frontal lobes
initiate most voluntary motor behavior:
- prefrontal cortex –> plans complex behavior
premotor cortex–> organizes and coordinates complex sequences
primary motor cortex–> produces focal skilled movements
damage to premotor cortex
cannot put motor sequences together
- cant push through with 1 finger and catch it
cannot coordinate movement
primary motor cortex function
producing focal skilled movements ex. arms, hands and mouth
- damage to M1 shows difficulty reaching and shaping fingers to perform various hand grasps
brainstem: species-typical movement
hess:
- stumlate diff areas of brainstem and produce species typical behaviors
1. brainstem controls
2. species typical behaviors are complex and coordinated
3. behaviors are adaptive: vary with context
species typical behavior
actions produced by every member of species
ex. whales breaching
spinal cord: executing movement
SC executes complex movements w/o brain
ex. scratching, walking, reflexes
damageL quad/paraplegia
motor homonculus
spatial represnetation of body in motor cortex
distorted by: size of representation and discontinuous
- represents repertoire of fundamental movement categories similar to language
role of motor cortex neurons
plan and initiate movements exxecut emovement code force of movement movement position - subthreshold activity in MC may underlie ability to imagine movement
plasticity in MC
without: hand area becomes smaller and elbow/shoulder larger
with: hand area retains size and retain some ability to move hand
constraint: forces use of affected limb in stroke induced limb paralysis
corticospinal tract: MC to muscle
main descending pathway from motor cortex (efferent)
- descend into BS
- emerge on ventral surface to form pyramidal tract where axons dessucate
2 descending paths of CS tract
lateral: decussates at brainstem, moves digits/limbs
(extremeties, contralateral)
ventral/anterior: same side of brain, moves midline on same side of body (trunk/ipsilateral)
CS in spinal cord
terminate in spinal cord
- synapses with interneurons and motor neurons
- motor neurons carry commands to muscles
basal ganglia
subserve wide range of functions, association or habit learning, motivation, emotion, motor control
input from neocortex and dopaminergic system from substantia nigra
project back to motor cortex (recipricol loop)
hyperkinetic disorders
striatum damage causes unwanted writhering twitching movements and too much force (huntingtons, tourettes)
hypokinetic disorders
damage to basal ganglia leads to loss of motor ability, rigidity, trouble initiating / producing movements, not enough force (parkinsons)
volume hypothesis
internal globus pallidus (GPi) acts like a volume control on motor cortex: turned up = movement blocked, turned down = movement allowed
direct: inhibited GPi and produces movement
indirect: activated GPi and blocks movement
cerebellum
involved in refined execution and timing of movement
lobes: anterior, posterior, flocculur
hemispheres: homuncular organization, lateral (limbs, hands, feet), medial (face and midline of body)
experimental clues to cerebellums role
- cerebllar patients and movement corrections: many movements require rapid updating and correction from cerebellum
- monkeys trained to point with/without prism glasses , learned adaption in long term motor learning
- cerebellum compares intended movement with actual movement and reports errors for correction
