Physiology - Muscle reflexes

Question 1

What does alpha motor efferent (from spinal cord) innervate?

Answer 1

extrafusal muscle fibers and cause contraction

Question 2

What does gamma motor efferent (descending fiber from brain) innervate?

Answer 2

• intrafusal muscle fibers (muscle spindle) and responsible for muscle tone (high gain)

Question 3

What will a stimulatory signal that passes through the interneuron do to muscle contractions?

Answer 3

• An inhibitor for muscle contractions

Question 4

What type of contraction are intrafusal muscle fibers responsible for?

Answer 4

• isometric only - no shortening. They do allow the muscle spindle to be taut allowing any small changes in muscle spindle to be detected

Question 5

What is characteristic of the center of the intrafusal muscle fibers

Answer 5

no myofibrils in the center therefore no contractions

Question 6

What does gamma-d and gamma-s detect?

Answer 6

gamma-d detects static (slow stretch - little effect on nuclear bags)
gamma-s detects dynamic (rapid stretch)

Question 7

What are extrafusal muscle fibers involved in?

Answer 7

• involved in muscle contraction, innervated by alpha motor neurons, coming out of the anterior horn

Question 8

Patients with upper motor neuron disease cannot sense what?

Answer 8

Gamma motor neurons are not sensing any stretch (ex. can’t see space with eyes closed)

Question 9

What will tapping of the patellar ligament evoke?

Answer 9

stretch –> streched spindle activating the alpha motor neuron –>which stimulates extrafusal muscle fibers to contract.

Question 10

Where is the Golgi Tendon organ and what is the information that it sends?

Answer 10

• Located within the actual tendon of the muscles. Upon excessive stretching it detects length or rate of change.

Question 11

How does the GTO protect the muscles?

Answer 11

It sends afferent signals to the spinal cord, cerebellum, and other brain areas. It also sends out local inhibitory signals to stop contraction. It accomplishes this by equalizing tension among all muscle fibers by spreading load over ALL muscle fibers

Question 12

In leg what occurs upon stimulation of painful stimuli.

Answer 12

Activation of contrallateral leg extension to counterbalance weight

Question 13

Is there atrophy in the UMN lesions or LMN lesion? Why?

Answer 13

There is atrophy in the LMN lesions and No atrophy in the UMN lesions due to hyperreflexive state that basically leads to tone.

Question 14

Are there fasciculation in an UMN lesion or a LMN lesion?

Answer 14

There is Fasciuclations in the LMN lesion only

Question 15

Are reflexes increased or decreased in an UMN or LMN lesions?

Answer 15

UMN (probably again due to hyper reflexive state)

Question 16

Is tone increased for UMN lesions or LMN lesions?

Answer 16

UMN (guess why)

Question 17

Which type of lesion (UMN or LMN) presents a with a positive babinski sign.

Answer 17

UMN

Question 18

What is the babinski sign?

Answer 18

Stroking the sole of the foot cuases an abnormal fanning of the toes and the extension of the big toe indicating corticospinal pathway damage.