28: Motor Reflexes

Question 1

Four characteristics of reflexes

Answer 1

Involuntary, fast, short-acting, precise

Question 2

Three spinal reflexes

Answer 2

1. Myotatic
2. Golgi tendon reflex
3. Crossed extensor reflex

Question 3

Five brainstem/midbrain reflexes

Answer 3

1. Vestibular
2. Righting reflex
3. Suckle reflex
4. Yawning
5. Eye/head movements

Question 4

Two cortical reflexes

Answer 4

1. Placing reaction

2. Hopping reaction

Question 5

Purpose of the Golgi tendon reflex

Answer 5

Protect muscle from damage due to excess force

Question 6

Purpose of myotatic reflex

Answer 6

Protect muscle from tearing due to stretch

Question 7

Golgi tendon and myotatic reflexes: poly vs monosynaptic

Answer 7

Golgi tenon: polysnaptic

Myotatic: monosynaptic

Question 8

Golgi tenon organs

Answer 8

Bare nerve endings with many branches innervating tendons

Question 9

Conduction velocity of 1a vs 2a fibers

Answer 9

1a: higher conduction velocity than 2a

Question 10

Spinal shock

Answer 10

With transection of the SC, all reflexes are abolished, even if circuit is still intact

Question 11

How to recover reflexes after spinal shock

Answer 11

1. Axonal sprouting below transection

2. Expression of self-activating receptor phenotypes (ex: 5HTC)

Question 12

Brainstem facilitatory vs inhibitory region

Answer 12

Facilitatory region: activates gamma motor neurons -> muscle spindle more sensitive
Inhibitory region: inhibits gamma motor neurons -> muscle spindle less sensitive

Question 13

Which region is spontaneously active vs needs activation from cortical region: brainstem facilitatory vs inhibitory regions

Answer 13

Facilitatory region: spontaneously active

Inhibitory region: requires activation from cortical regions

Question 14

What happens to brainstem inhibitory region with loss of cortex?

Answer 14

Inhibitory region cant be activated, so facilitatory region dominates, causing spasticity

Question 15

Decerebrate posturing

Answer 15

Contraction of all anti-gravity/extensor muscles

Question 16

Decorticate posturing

Answer 16

Flexion of UE joints + extension of LE joints

Question 17

What causes decerebrate posturing?

Answer 17

Loss of all structures rostral to pons

Question 18

Rigidity vs spasticity in decerebrate posturing

Answer 18

Rigidity: resists motion in all directions due to contractions
Spasticity: resists motion in a given direction due to hyperactive myotatic reflex

Question 19

What causes spasticity in decerebrate posturing

Answer 19

Continual activation of gamma motor neurons via brainstem

Question 20

What causes flexion of UE joints in decorticate posturing vs extension of LE joints

Answer 20

UE flexion: disinhibition of red nucleus

LE extension: disinhibition of reticuospinal + vestibulospinal pathways

Question 21

Which one relies on head positioning, decerebrate or decorticate posturing?

Answer 21

Decorticate

Question 22

Unilateral decorticate posturing

Answer 22

Common with strokes that are in the vicinity of the internal capsule