Motor Control: Reflexes Flashcards Preview

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Flashcards in Motor Control: Reflexes Deck (29)
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1
Q

Motor Control:

Cortical

A
  • Placing reaction

* hopping reaction

2
Q

Motor Control:

Spinal Reflexes

A
  • stretch (myotatic)
  • golgi tendon reflex
  • crossed extensor
3
Q

Motor Control:

Brainstem/Midbrain

A
  • vestibular
  • righting reflex
  • suckle*
  • yawn*
  • eye/head movements*
4
Q
  • contraction (shortening) of a stretched muscle
  • Protect muscle from tearing due to stretch.
  • initiated by MUSCLE SPINDLE.
  • MONOSYNAPTIC, segmental reflex.
A

myotatic reflex

5
Q

myotatic reflex:

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

A

MUSCLE SPINDLE

6
Q

myotatic reflex:

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

intrafusal fibers

7
Q

myotatic reflex:

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

extrafusal fibers

8
Q

myotatic reflex:

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

motor and sensory

9
Q
myotatic reflex:
?
•is not contractile.
•Is the portion sensitive to length.
•Is actually TWO sensors - with different afferents
- ?
- ?
A
  • The sensory portion of a muscle spindle
  • nuclear bag fiber
  • nuclear chain fiber
10
Q

myotatic reflex:

Nuclear chain and bag are innervated by?

A

1a fiber (primary afferent)

large and myelinated

11
Q

myotatic reflex:

Primary afferent is sensitive to both:

  • ?
  • ?
A
  • length of muscle

* how fast the length is changing.

12
Q

myotatic reflex:

Secondary Afferent Characteristics:

  • smaller, myelinated ? fiber
  • innervates only the ?.
  • sensitive only to the ? of the muscle.
A
  • Group II
  • nuclear chain fiber
  • length
13
Q

myotatic reflex:

The motor portion consists of the?

A

intrafusal contractile elements

14
Q

myotatic reflex:

intrafusal contractile elements characteristics:

  • same histology as ?
  • innervated by a ?.
  • Control the ? of the sensory portion **
A
  • skeletal muscle
  • gamma motoneuron
  • length
15
Q

myotatic reflex:

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

alpha- motoneuron

16
Q
  • sudden (abrupt) relaxation of a contracted muscle.
  • Protect muscle from damage due to excessive force.
  • initiated by golgi tendon organ.
  • POLYSYNAPTIC, segmental reflex.
A

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

17
Q
  • innervate tendon
  • bare nerve ending with lots of branches.
  • Action potentials increase w/ tension.
  • Ib fiber to spinal cord. **
A

Golgi Tendon Organs

18
Q

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
A
  • interneuron

- GABA

19
Q

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 ?

A
  • higher

- Central Modification

20
Q

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

A

Spinal Shock

21
Q

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

  • ?
  • ?
A
  • Axonal sprouting below the level of the transection.

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

22
Q

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

A

Decerebrate Posturing

23
Q

Decerebrate Posturing:

•resists motion in all
directions.

•Results from maintained
muscle contraction.

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

A

Rigidity

24
Q

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
A

Spasticity

25
Q

Spasticity:

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

Brainstem facilitatory region

26
Q

Spasticity:

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

Brainstem inhibitory region

27
Q

Spasticity:

  • With the loss of the cortex, the ? region is not activated, leaving the ? to dominate.
A
  • brainstem (-)

- (+) region

28
Q

•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)

A

Decorticate posturing (rigidity)

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

29
Q

Decorticate posturing (rigidity)

-likely unilateral

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

- stroke