Week 6 LIs

Question 1

Feedforward

Answer 1

postural adjustments for voluntary movement take place in anticipation of movement

Question 2

feedback

Answer 2

postural adjustments for voluntary movement that take place in response to postural instability that results from moveemnt

Question 3

feed forward mechanism involves

Answer 3

(cortico)reticulospinal pathway

Question 4

feedback mechanisms rely on

Answer 4

• proprioceptive, vestibular, and visual afferents are mediated in large part through local spinal reflexe, the vestibulospinal pathways, and erebellum

Question 5

activity in various motor pathways coordinated

Answer 5

1. Decision made to move
2. UMNs in motor cortex project motor command
3. Movement of limb may produce unanticipated postural instability
4. Posture corrected

Question 6

decision made to move

Answer 6

motor plan is constructed in cerebral cortical and subcortical networks including

• limbic structures
• association areas of neocortex
• basal ganglia
• motor command ultimately carried by UMNs in motor cortex

Question 7

UMNS in motor cortex project the motor command to

Answer 7

1. motor neuron pools involved in directed limb movement (Lateral Motor pathways; corticospinal, (cortico)rubrospinal
2. motor neuron pools involved in anticipatory postural adjustments (medial motor pathways; (cortico)Reticulospinal)

Question 8

Motor neuron pools involved in directed limb movements

Answer 8

• projections to LMNs may be direct via coritcospinal tract
• more often cortical UMNs synapse on UMNs in red nucleus and reticular formation which then project to LMNs in spinal cord to control directed limb movements or protraction of limb for locomotion

Question 9

motor neuron pools involved in anticipatory posutural adjustments

Answer 9

• cortical UMNs project on Reticulospinal UMNs which project to LMNs controlling postural muscles; contraction in postural muscles precedes contraction of muscles involved in desired movement
• coticospinal UMNs may also project directly to spinal cord to control postural LMNs

Question 10

reticulospinal UMNs also recieve input from

Answer 10

vestibular system and spinal cord, can use this information to construct a motor plan anticipating necessary postural adjustments

Question 11

movement of limb produces unanticipated postural instablity

Answer 11

which is detected by proprioceptors, the vestibular system, and/ or the visual system

Question 12

rapid feedback correction of posture achieved largely via

Answer 12

• local reflexes
• vestibulospinal pathways
• cerebeullum
• these all receive various aspects of sensory feedback

Question 13

decerebrate rigidity caused by severe lesions of

Answer 13

brainstem in midbrain and/ or pons (usually midbrain)

Question 14

animals with decerebrate rigidity demonstrate

Answer 14

• excessive extensor tone in all 4 limbs
• opisthotonus
• severely altered state of consciousness

Question 15

opisthotonus

Answer 15

hyperextension of neck and back

Question 16

profoundly altered consciousness w/ decerebrate rigidity

Answer 16

b/c major population of ascending reticular activating system in midbrain

Question 17

lesions of cd midbrain with decerebrate rigidity

Answer 17

most dramatic effect bc essentially removes all motor cortex and red nucleus UMN influence w/ in motor system

Question 18

what do UMNs knocked out in decerebrate rigidity normally do

Answer 18

• facilitate flexors
• inhibit extensors
  so if these are knocked out then nothing is facilitating flexors nor inhibiting extensors so you end up with excessive extensor tone

Question 19

Cerebral cortex facilitates UMNs of

Answer 19

medullary reticular formation so lesion in midbrain/ pons -> these UMNs being significantly less active

Question 20

impact of cortical input removal on vestibulospinal and pontine reticulospinal UMNs

Answer 20

minimal impact bc these receive excitatory input from vestibular apparatus and spinal cord, do not require cortical input to be active
- will continue to facilitate extensor muscles with little to no counter regulation from corticospinal, rubrospinal, and medullary reticulospinal pathways
aka excitatory input remains for extensors but nothing facilitating flexors -> decerebrate rigidity bc all the other pathways are knocked out