Motor Control: Reflexes

Question 1

Motor Control:

Cortical

Answer 1

• Placing reaction

* hopping reaction

Question 2

Motor Control:

Spinal Reflexes

Answer 2

• stretch (myotatic)
• golgi tendon reflex
• crossed extensor

Question 3

Motor Control:

Brainstem/Midbrain

Answer 3

• vestibular
• righting reflex
• suckle*
• yawn*
• eye/head movements*

Question 4

• contraction (shortening) of a stretched muscle
• Protect muscle from tearing due to stretch.
• initiated by MUSCLE SPINDLE.
• MONOSYNAPTIC, segmental reflex.

Answer 4

myotatic reflex

Question 5

myotatic reflex:

-Contains both afferent (sensory) and efferent (contractile) components

Answer 5

MUSCLE SPINDLE

Question 6

myotatic reflex:

• Because the capsule is “fusiform”, the fibers within the capsule are called?

Answer 6

intrafusal fibers

Question 7

myotatic reflex:

• The muscle fibers that make up the bulk of the muscle are called the?

Answer 7

extrafusal fibers

Question 8

myotatic reflex:

• The intrafusal fibers of the muscle spindle have both ? and ? components

Answer 8

motor and sensory

Question 9

myotatic reflex:
?
•is not contractile.
•Is the portion sensitive to length.
•Is actually TWO sensors - with different afferents
- ?
- ?

Answer 9

• The sensory portion of a muscle spindle
• nuclear bag fiber
• nuclear chain fiber

Question 10

myotatic reflex:

Nuclear chain and bag are innervated by?

Answer 10

1a fiber (primary afferent)

large and myelinated

Question 11

myotatic reflex:

Primary afferent is sensitive to both:

• ?
• ?

Answer 11

• length of muscle

* how fast the length is changing.

Question 12

myotatic reflex:

Secondary Afferent Characteristics:

• smaller, myelinated ? fiber
• innervates only the ?.
• sensitive only to the ? of the muscle.

Answer 12

• Group II
• nuclear chain fiber
• length

Question 13

myotatic reflex:

The motor portion consists of the?

Answer 13

intrafusal contractile elements

Question 14

myotatic reflex:

intrafusal contractile elements characteristics:

• same histology as ?
• innervated by a ?.
• Control the ? of the sensory portion **

Answer 14

• skeletal muscle
• gamma motoneuron
• length

Question 15

myotatic reflex:

• Within the spinal cord, the Ia afferent from the muscle spindle synapses directly onto the ? innervating the stretched muscle.

Answer 15

alpha- motoneuron

Question 16

• sudden (abrupt) relaxation of a contracted muscle.
• Protect muscle from damage due to excessive force.
• initiated by golgi tendon organ.
• POLYSYNAPTIC, segmental reflex.

Answer 16

Golgi Tendon reflex
(aka inverse myotatic)
(aka autogenic inhibition)

Question 17

• innervate tendon
• bare nerve ending with lots of branches.
• Action potentials increase w/ tension.
• Ib fiber to spinal cord. **

Answer 17

Golgi Tendon Organs

Question 18

Golgi Tendon reflex:
- The motoneuron is inhibited by the activation of the spinal ? (via release of ?)

• Abrupt relaxation of the muscle occurs, returning the Golgi Tendon organ discharge rate back to normal

Answer 18

• interneuron

- GABA

Question 19

The ? centers of the brain are often seen to be inhibitory to the reflexes, but certain regions do provide an excitatory input. This is called ?

Answer 19

• higher

- Central Modification

Question 20

Even though the neurons producing the reflex are below the level of the transection (and are therefore intact), the reflex fails to occur.

Answer 20

Spinal Shock

Question 21

Recovery of reflexes from Spinal Shock is believed to result from:

• ?
• ?

Answer 21

• Axonal sprouting below the level of the transection.

* Expression of receptor phenotypes that are self- activating (5HTC receptor).

Question 22

Results from loss of all structures rostral to the pons (caudal to the red nucleus).

Answer 22

Decerebrate Posturing

Question 23

Decerebrate Posturing:

•resists motion in all
directions.

•Results from maintained
muscle contraction.

•Continual activation of
ALPHA-MOTONEURONS
- Brainstem is activating alpha – motoneurons

Answer 23

Rigidity

Question 24

Decerebrate Posturing:

•resists motion in a given
direction.

•Myotatic reflex
hyperactive.

•Continual activation of
GAMMA-MOTONEURONS
- contracts intrafusal muscle. 
- Lengthens nuclear bag/chain fibers. 
- brainstem

Answer 24

Spasticity

Question 25

Spasticity:

• by activating the gamma-motoneurons, makes muscle spindle more sensitive.
• This region is spontaneously active.

Answer 25

Brainstem facilitatory region

Question 26

Spasticity:

• inhibits gamma motoneurons, making muscle spindle less sensitive.
• This region requires activation from cortical regions.

Answer 26

Brainstem inhibitory region

Question 27

Spasticity:

• With the loss of the cortex, the ? region is not activated, leaving the ? to dominate.

Answer 27

• brainstem (-)

- (+) region

Question 28

•Flexion of the upper limb joints (disinhibition of red nucleus & its
control of UE flexors).

•Extension of the lower limbs (disinhibition of reticulospinal and
vestibulospinal pathways)

•Dependent on head position (release of postural reflexes)

Answer 28

Decorticate posturing (rigidity)

(likely unilateral)
(results from strokes in the vicinity of the internal capsule
• a relatively common site for a stroke.

Question 29

Decorticate posturing (rigidity)

-likely unilateral

• results from strokes in the vicinity of the ?
• a relatively common site for a ?.

Answer 29

• internal capsule

- stroke