Posture and tone

Question 1

Goal of posture

Answer 1

Keep the center of mass above the support surface

Question 2

Muscle tone and balance

Answer 2

Provides force in the opposite direction of shift to help maintain balance

Question 3

Postural tone mechanism

Answer 3

Tonic activity in muscles (usually physiological extensors). Tonic activity of alpha motor neurons

Question 4

How do you increase postural tone directly?

Answer 4

Increase alpha motor neuron activity through direct projections (input from descending tracts)

Question 5

How do you increase postural tone indirectly?

Answer 5

Increase gamma motorneuron activity. Descending projections and relax feedback through stretch receptors

Question 6

Fast postural adjustment types

Answer 6

Feedforward/anticipatory (includes retinculospinal tracts). Feedback (includes vestibulospinal)

Question 7

Medial vestibulospinal tract

Answer 7

Head and neck muscles

Question 8

Lateral vestibulospinal tract

Answer 8

Axial and proximal limb muscles

Question 9

Inputs for the vestibulospinal tract

Answer 9

Vestibular organs and cerebellum

Question 10

vestibulospinal tract and posture

Answer 10

Contact alpha and gamma motorneurons. Sense when off-balance and adjust the muscle tone (feedback).

Question 11

Which reflex acts on the neck muscles to adjust the head?

Answer 11

Vestibulocollic reflex

Question 12

Which reflex adjust the limbs?

Answer 12

Vestibulospinal reflex

Question 13

What other descending systems help provide postural control?

Answer 13

Corticospinal, rubrospinal, reticulospinal

Question 14

How do other descending systems help provide postural control?

Answer 14

Adjust reflex sensitivity. Enable feedforward adjustments for self-generated movements

Question 15

What does the corticoreticular and reticulospinal tracts do to help maintain posture?

Answer 15

Coordination of proximal limbs and trunk.

Anticipatory adjustments

Question 16

What is excited and what inhibits the pontine reticular formation?

Answer 16

Excites gamma motorneurons.. Inhibited by cortex

Question 17

What is inhibited and what excites the medullary reticular formation?

Answer 17

Inhibits gamma motorneurons. Excited by cortex.

Question 18

What is the net effect of the interactions between the medullary and pontine reticular formations?

Answer 18

Cortex damps down gamma motor neuron activity

Question 19

Pyramidal tract lesion

Answer 19

Loss of fine voluntary movements of the hands

Question 20

What tract controls hand movements?

Answer 20

Corticospinal tract

Question 21

Spinal cord transection (immediately afterward)

Answer 21

Lose ALL descending systems. No excitatory drive. Flaccidity, no relfexes (alpha and gamma motor neurons have lost their input from the central nervous system

Question 22

Spinal cord transection (2 months later)

Answer 22

Hyperreflexia and hypertonia. Axons extremely sensitive and compensating

Question 23

Upper motor neuron syndrome presentation immediately after injury

Answer 23

Initial weakness (paresis)
Hypotonia ("spinal shock")

Question 24

UMN syndrome presentation after several days

Answer 24

Babinski’s sign

Spasticity (increased tone, hyperreactive reflexes, clonus, clasp-knife rigidity

Question 25

What happens to the reticulospinal tract with a UMN lesion?

Answer 25

Increased gamma motor neuron activity causing increase tone

Question 26

Possible treatment for UMN syndrome?

Answer 26

Snip dorsal root (trying to get at Ia). Prevents feedback loop and causes reduction in spasticity cycle.

Question 27

Decoriate posture

Answer 27

• Almost always caused by damage above red nucleus
• Upper extremities are in flexion
• Lower in flexion
• Brainstem motor centers functioning, but not getting input from the cortex

Question 28

Decerebrate posture

Answer 28

• Progression of decoriate
• Loss of red nucleus
• No modulation of reticulospinal tract
• All limbs in extension
• Flaccidity–>will likely lead to death