Motor system 2

Question 1

Define hierarchical organization of motor system

what are components

Answer 1

1) muscles and motoneurons and spinal reflex = effectors doing work
2) muscles/nuerons organized by CPG in spinal cord that control timing of output

Question 2

CPG are subject to control from where?

and where are these areas receiving central input for volitional intent

Answer 2

projection regions = brainstem, motor cortex

above these areas, premotor cortical area + supplemental cortical area are important

Question 3

reason for hierarchical org of motor system

Answer 3

basic movement can occur auto and modifications occur with little to no conscious though

so brain more directed to important goals

cerebellum helps

Question 4

Describe CPG

allows for what limb movement

Answer 4

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

Question 5

describe simple rhythmic movement controlled by CPG

distinguish between stance and swing phase

Answer 5

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

Question 6

what happens if dorsal roots cut so lumbar cord gets no sensory input

Answer 6

legs still move in normal pattern if body is supported

Question 7

where are CPGs located

what do they consist of

what are they consciously controlled by

are they like pacemakers

Answer 7

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

Question 8

describe somatotopic organization of primary motor cortex

Answer 8

feet most medial
head lateral and ventral
distortion so face and hands have most nnerv

Question 9

describe somatotopic organization of primary motor cortex

lateral and ventral premotor cortex
1) function

Answer 9

motor planning
esp for movements triggered by external sensory events

plans actions for execution without delay such as conforming hand for grasping

Question 10

describe somatotopic organization of primary motor cortex

supplementary motor cortex

Answer 10

motor planning
esp for movements initiated internally

and mental rehearsal of pattern of moves
ex = thinking about moving fingers

Question 11

is locomotion possibly mediated by spinal CPG for gait in cord?

Answer 11

spinal prep

yes
patterned activity seen when animal suspended over treadmill after thoracic cord transection

Question 12

is locomotor activity dependent on sensory input

Answer 12

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

Question 13

is locomotor activity driven by brainstem?

Answer 13

decerebrate prep

yes because lose spontaneous locomotor activity transect caudal to mamillary body –> mesencephalic locomotor center

Question 14

why lose muscle tone in LMN syndrome

what drives spontaneous twitches

Answer 14

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

Question 15

brainstem control of movement

Answer 15

1) organize axial musculature
2) maintain balance
3) regulate posture
4) orient gaze

Question 16

corticospinal and rubrospinal pathways controlling __-

Answer 16

precise skilled movements involving distal parts of the limbs (hands)

Question 17

locomotro patterning after spinal cord injury

Answer 17

potential for plasticity because most lesions leave peripheral loci and conserve basic oscill circuits

Question 18

optogenetics to study neural circuits

Answer 18

use light sensitive ion channels to open or close channels

introduce channels to specific neurons in diff circuits and see how they affect behavior

Question 19

pathway of reticulospinal tract

function

Answer 19

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

Question 20

pathway of vestibulospinal tract

Answer 20

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)

Question 21

superior colliculus/tectospinal/corticospinal tract function

Answer 21

orienting movements (gaze and stance) towards unexpected stim