Lecture 6 - LMNs

Question 1

Where do LMNs start?

Answer 1

In the spinal cord

Question 2

What is the myotactic reflex?

Answer 2

pre-programmed response by the body to something that causes the muscle to stretch

Question 2

Regarding the face, if the left hemisphere is damaged, then what might result?

Answer 2

the right upper face will experience weakness, since it receives impulses from the right hemisphere. right lower face will be damaged, since it receives impulses from the left hemisphere

Question 3

If there’s LMN damage on the left side of the brain, then what might happen to one’s face?

Answer 3

left side of the face is droopy, since LMNs innerve ipsilaterally

Question 4

If the tongue is deviated, fasciculates are present, and hemifacial droop, then what cranial nerve is damaged?

Answer 4

CN VII

Question 5

If an individual has a right UMN stroke, then what are the symptoms?

Answer 5

tongue deviation to the left; lower part of the face is intact, but the upper part of the face may experience weakness

Question 6

Alpha LMNs innervate _________.

Answer 6

voluntary muscles

Question 7

Gamma LMNs deal with _______

Answer 7

stretch and tension

Question 8

LMN start in the ________

Answer 8

brainstem and spinal cord

Question 9

UMN start in the ______

Answer 9

cerebral cortex, particularly PMA and primary somatosensory cortex

Question 10

What is the purpose of the gamma loop?

Answer 10

to maintain muscle tone

Question 11

Alpha LMNs activate ______ , whereas gamma LMNS activate ________

Answer 11

extrafusal fibers; intrafusal fibers

Question 12

What pathway innervates the gamma loop?

Answer 12

the indirect pathway, particularly reticulospinal tract

Question 13

What is the final common pathway consist of?

Answer 13

Lower motor neurons of PNS; 12 pairs of cranial nerves and 31 pairs of spinal nerves

Question 14

UMN lesions are characterized by

Answer 14

spasticity, no atrophy, no fasciculations, weakness, increased muscle tone, ataxia, babinski sign, hypo or hyperkinesia

Question 15

LMN lesions are characterized by

Answer 15

flaccidity, atrophy, fasciculations, weakness, decreased muscle tone, paresis, paralysis, fibrillations

Question 16

The final common pathway has two important sensory receptors. They are ____ and _____

Answer 16

1a and 1b

Question 17

The sensory receptor _____ is responsible for stretch, whereas the sensory receptor _____ is responsible for tension.

Answer 17

1A and 1B

Question 18

What inputs do alpha LMNs receive?

Answer 18

spinal interneurons, upper motor neurons, and sensory input from muscle spindles

Question 19

What inputs do alpha LMNs receive for proprioception?

Answer 19

monosynaptic A.K.A myotactic; multisynaptic; direct activation pathways

Question 20

What are the components of the gamma loop?

Answer 20

alpha LMN, gamma LMN, intrafusal fibers, input from the indirect activation pathway (most likely the reticulospinal tract), sensory receptors i muscle spindles

Question 21

There are more muscle spindles in the ______ tract than in the _______ tract

Answer 21

corticospinal; corticobulbar

Question 22

What parts of the body have many muscle spindles?

Answer 22

jaw muscles, especially the masseter; recurrent and superior laryngeal; pharyngeal muscles; optic-oculomotor muscles; stapedius muscle

Question 23

What parts of the body have few muscle spindles?

Answer 23

tongue, lips, face (except for eyes and jaw)

Question 24

For tension, golgi tendon organs fire and then what happens?

Answer 24

golgi tendon organs fire and stimulate 1b sensory receptors in the muscle spindles. Then 1b sensory receptors stimulate interneurons. The interneurons stimulate alpha LMNs which then contracts the extrafusal fibers in the muscle.

Question 24

For stretch, gamma LMNs fire and then what happens?

Answer 24

intrafusal fibers contract; this signals to alpha LMNs to innervate extrafusal fibers to contract and match the length of the intrafusal fibers

Question 25

What are fasciculations?

Answer 25

brief local twitching

Question 26

What are fibrillations?

Answer 26

a consequence of a LMN lesion; regular contractions caused by slow repetitive action potentials