3.18.14 34 Motor Systems V (Posture and Locomotion)

Question 1

Descending systems regulate posture via what two mechanisms

Answer 1

Tonic excitatory bias to extensor motor pathways

Opening and closing spinal reflexes

Question 2

Central influence on spinal reflexes have longer or shorter latencies?

Answer 2

Longer (120 msec vs. 50 msec mytotatic stretch reflex)

Question 3

The stretch reflex is modulated such that reflexes that stabilize posture are (facilitated/weakened) and those that destabilize are (f/w)

Answer 3

Those that stabilize are facilitated
Those that destabilize are weakened
DUH

Question 4

Regarding the tonic neck reflex, dorsiflexion elicits what response in forelimb and hindlimb? Ventroflexion?

Answer 4

Dorsiflexion (think of a cat landing after a leap):
-Hindlimbs flex
-Forelimbs extend
—
Ventroflexion (think of a cat leaping forward):
-Hindlimbs extend
-Forelimbs flex

Question 5

Regarding the decorticate condition, describe the reflexes elicited if the head is turned to the right.

Answer 5

Head turned RIGHT
RIGHT arm is extended
LEFT arm is flexed

Arm extends where the head is turned

Question 6

Describe the decorticate condition (head facing forward)

Answer 6

Arms flexed, legs extended

Question 7

Describe the decerebrate condition (head facing forward)

Answer 7

Arms and legs extended, head dorsiflexed

Question 8

Descending messages from supraspinal centers for the purpose of locomotion can best be described as

Answer 8

Rhythmic locomotor output

Question 9

The rhythm pattern is generated by what structure? Where?

Answer 9

Locomotor oscillators

Cervical and Lumbar enlargements of the spinal cord

Question 10

T/F: Opposite limbs are dependent upon the same generator within the spinal cord

Answer 10

False: individual pattern generators exist for each limb; activity in one is independent of activity in the other

Question 11

What role to gamma motor neurons play in locomotion?

Answer 11

Coactivation of gamma and alpha motor neurons ensures that the muscle spindle is appropriately calibrated to muscle length during motion in order to respond to external stimuli

Question 12

What pathways project onto locomotion oscillators as supraspinal influence over locomotion?

Answer 12

Reticulospinal and vestibulospinal tracts

Question 13

What is the primary structure that receives cortical and basal ganglia inputs, thereby influencing oscillators via the reticulospinal tract?

Answer 13

Mesencephalic locomotor region

Question 14

What does the mesencephalic locomotor region do?

Answer 14

Receives cortical and basal ganglia inputs; influences locomotion oscillators via the reticulospinal tract

Question 15

What information does the dorsal spinocerebellar tract send to the cerebellum?

Answer 15

Information about muscle activity via peripheral modulators (stretch receptors, skin receptors, ect.)

Question 16

What information does the ventral spinocerebellar tract send to the cerebellum?

Answer 16

A copy of the programmed movements generated by the locomotion oscillators

Question 17

The swing phase of locomotion is mediated by (flexors/extensors)?

Answer 17

Flexors

Question 18

The stance phase of locomotion is mediated by (flexors/extensors)?

Answer 18

Extensors

Question 19

The basal ganglia is involved in what two major functions? What symptoms result from lesion?

Answer 19

Initiation/termination of movement
Maintenance of center of gravity during postural changes
–
Akinesia (initiation), imbalance

Question 20

The cerebellum is involved in what major function? What symptoms result from lesion?

Answer 20

Dysmetria, ataxia