Motor system 2 Flashcards
Define hierarchical organization of motor system
what are components
1) muscles and motoneurons and spinal reflex = effectors doing work
2) muscles/nuerons organized by CPG in spinal cord that control timing of output
CPG are subject to control from where?
and where are these areas receiving central input for volitional intent
projection regions = brainstem, motor cortex
above these areas, premotor cortical area + supplemental cortical area are important
reason for hierarchical org of motor system
basic movement can occur auto and modifications occur with little to no conscious though
so brain more directed to important goals
cerebellum helps
Describe CPG
allows for what limb movement
generates intrinsic rhythm for coord movement via central command centers in spinal cord
produce patterned rhythmic output without sensory or central input
allows for limbs to alternate when walking driven by alternating rhythm of flexor and extensor motor neurons and interneurons in cord
describe simple rhythmic movement controlled by CPG
distinguish between stance and swing phase
1) stance phase = extensors fully activated to support foot planted on ground
contract extensor relax flexor
2) swing phase = flexor contraction raises leg off ground and swings
contract flexor relax extensor
what happens if dorsal roots cut so lumbar cord gets no sensory input
legs still move in normal pattern if body is supported
where are CPGs located
what do they consist of
what are they consciously controlled by
are they like pacemakers
located in cord
consist of flexor and extensor neurons firing out of phase
one CPG per leg
controlled by mesencephalic locomotor region btwn inferior and superior colliculus
not pacemaker; because CPG use excitatory inhib interneurons for rhythmic alternating activity
describe somatotopic organization of primary motor cortex
feet most medial
head lateral and ventral
distortion so face and hands have most nnerv
describe somatotopic organization of primary motor cortex
lateral and ventral premotor cortex
1) function
motor planning
esp for movements triggered by external sensory events
plans actions for execution without delay such as conforming hand for grasping
describe somatotopic organization of primary motor cortex
supplementary motor cortex
motor planning
esp for movements initiated internally
and mental rehearsal of pattern of moves
ex = thinking about moving fingers
is locomotion possibly mediated by spinal CPG for gait in cord?
spinal prep
yes
patterned activity seen when animal suspended over treadmill after thoracic cord transection
is locomotor activity dependent on sensory input
deafferented prep
no, if transect dorsal roots innerv limbs –> still observe rhythmic locomotor pattern if circuit stim with L-Dopa
NT is sufficient so doesn’t require sensory input
is locomotor activity driven by brainstem?
decerebrate prep
yes because lose spontaneous locomotor activity transect caudal to mamillary body –> mesencephalic locomotor center
why lose muscle tone in LMN syndrome
what drives spontaneous twitches
due to spindle involvement in maintaining tone (impair maintaining length of muscle by alpha motor neuron input on spindle)
change excitability of denervated muscle/abnormal activity of alpha motor neurons
brainstem control of movement
1) organize axial musculature
2) maintain balance
3) regulate posture
4) orient gaze
corticospinal and rubrospinal pathways controlling __-
precise skilled movements involving distal parts of the limbs (hands)
locomotro patterning after spinal cord injury
potential for plasticity because most lesions leave peripheral loci and conserve basic oscill circuits
optogenetics to study neural circuits
use light sensitive ion channels to open or close channels
introduce channels to specific neurons in diff circuits and see how they affect behavior
pathway of reticulospinal tract
function
1) from retic formation (contains mesencephalic locomotor) in pons
2) descend down brainstem and innerv motor neuron in medial ventral horn
important for posture, balance, and anticipatory movement esp when lose balance
ex = you contract gastroc before you contract bicep to maintain balance
pathway of vestibulospinal tract
1) originate in vestib nuclei
2) send output to spinal cord
unconsciously mediates balance and direction
activated during unexpected falls
(when fall back, arm back
when fall fwd, neck back and arm forward)
superior colliculus/tectospinal/corticospinal tract function
orienting movements (gaze and stance) towards unexpected stim
