Lecture 14: Motor Reflexes

Question 1

Cortical motor reflexes (2)

Answer 1

Placing reaction

Hopping reaction

Question 2

Brainstem/Midbrain reflexes (5)

Answer 2

Vestibular
Righting reflex
Suckling
Yawning
Eye/head movements

Question 3

Spinal reflexes (3)

Answer 3

Myotatic
Golgi tendon
Crossed extensor

Question 4

How many synapses in a myotatic reflex?

Answer 4

Monosynaptic

Question 5

What are the intrafusal fibers vs. extrafusal fibers?

Answer 5

Intrafusal fibers are within a capsule and extrafusal fibers are the noticable fibers.

Question 6

Intrafusal fibers have both:

Answer 6

Motor and sensory components

Question 7

Components of sensory portion of muscle spindle:

Answer 7

Nuclear bag

Nuclear chain

Question 8

What is the sensory portion sensitive to?

Answer 8

Sensitive to length of fibers

Question 9

What kind of nerves innervate the nuclear bag and chain? What are they sensitive to?

Answer 9

Ia fibers.

Length of muscle and how fast it is changing.

Question 10

When the sensory component senses changes in length, what happens?

Answer 10

An increase in APs

Question 11

Secondary afferent is what kind of fiber?
Innervates what?
Sensitive to?

Answer 11

Fiber: group II fiber
Innervates: nuclear chain fiber
Sensitive to: only length of muscle.

Question 12

What innervate the motor portion of the intrafusal part of the muscle spindle?
What is the motor neuron’s job?

Answer 12

Gamma motorneuron.

Controls the length of the sensory portion.

Question 13

When the intrafusal muscle contracts, what happens to the sensory portion?

Answer 13

The sensory portion stretches and is now more sensitive to a superimposed stretch

Question 14

What happens in the antagonist with the synapsing?

Answer 14

Ia afferent synapses on both the motoneuron of the strecthed muscle and the alphamotoneuron of the antagonist

Question 15

Appearance of golgi tendon reflex:

Purpose:

Answer 15

Sudden relxation of a contracted muscle.

Protect the muscle from damage from excessive force.

Question 16

How many synapses in the golgi tendon reflex?

Answer 16

Polysynaptic

Question 17

What does the GTO innervate?

What kind of fiber do they use?

Answer 17

The tendon.

Ib to the SC.

Question 18

Synaptic setup of the GTO

Answer 18

Ib from GTO activates the interneuron which inhibits the motoneuron.

Question 19

How do the higher centers of the brain effect reflexes?

Answer 19

They generally inhibit them

Question 20

Spinal shock

Answer 20

Temporary loss of reflexes after an injury to the SC.

Question 21

How does one overcome spinal shock?

Answer 21

Axons sprout below the level of the lesion.

Express self-activating receptors (serotonin).

Question 22

Decerebrate posturing looks like:

What causes it?

Answer 22

Extermities extended with wrists flexed at sides.

From loss of structures rostral to pons.

Question 23

What causes rigidity?

Answer 23

Continual activation of alpha-motoneurons

Question 24

What causes spasticity

Answer 24

Continual activation of gamma-motoneurons.

Question 25

Brainstem facilitory region

Answer 25

Activates gamma-motoneurons by making muscle spindle more sensitive.

Question 26

Brainstem inhibitory region

Answer 26

Inhibits gamma-motoneurons making muscle spindles less sensitive. Requires activation from cortical regions.

Question 27

End result of cortical damage on positioning:

Answer 27

Brainstem inhibitory region is NOT activated and facilitory region dominates. This leaves brainstem to dominate and causes spasticity.

Question 28

Decorticate posturing

Answer 28

Flexion of UE Extension of LE Depending on head position

Question 29

When will I see decorticate positioning?

Answer 29

Strokes in the internal capsule