Overview of Motor Systems

Question 1

What do LMNs innervate?

Answer 1

Skeletal Muscle

Question 2

What do the medial LMNs innervate?

Answer 2

Axial/Trunk Muscles

Question 3

What do the lateral LMNs innervate?

Answer 3

Distal Limb Muscles

Question 4

What do the dorsal LMNs innervate?

Answer 4

Flexor Muscles

Question 5

What do the ventral LMNs innervate?

Answer 5

Extensor Muscles

Question 6

What neurotransmitter do LMNs use?

Answer 6

Acetylcholine

Question 7

What are the types of motor units?

Answer 7

S-Unit
FR-Unit
FF-Unit

Question 8

Describe the S-Unit.

Answer 8

Slow twitch fibers that are fatigue resistant

Question 9

Describe the FR-Unit.

Answer 9

Fast twitch fibers that are fatigue resistant

Question 10

Describe the FF-Unit.

Answer 10

Fast twitch fast fatiguing fibers that have high force

Question 11

What are the red muscle fibers?

Answer 11

S-Unit

Question 12

What are the white muscle fibers?

Answer 12

FF-Unit and FR-Unit

Question 13

What are the descending pathways of the LMNs?

Answer 13

Corticospinal tract
Vestibulospinal tract
Reticulospinal tract
Tectospinal tract

Question 14

Describe the corticospinal tract.

Answer 14

All of it is excitatory and uses glutamate as the NT

Question 15

Describe the tectospinal tract.

Answer 15

It supplies the reflex turning of head to visual/auditory stimuli

Question 16

What are the higher cortical centers and their functions?

Answer 16

– Association cortex – “decide” that a movement is needed
– Supplementary motor area – planning/learning complex movements
– Premotor cortex – devise a “plan” for the movement
– Motor cortex – issues “commands” to motor neurons

Question 17

What are Betz cells?

Answer 17

They are large neurons in the motor cortex

and invoked in most leg movements with some hand too

Question 18

What are the contributions to the corticospinal tract?

Answer 18

50% from the primary motor cortex

Adjacent Frontal motor and Parietal areas contribute the rest of the CST fibers

Question 19

Where does the CST project to?

Answer 19

– spinal cord and brainstem

– collaterals (direct and indirect) to basal ganglia, thalamus, reticular formation, sensory nuclei

Question 20

What part of the internal capsule does the CST pass through?

Answer 20

Posterior Limb

Question 21

What is the main distinction in an UMN and LMN lesion in the face on CN VII?

Answer 21

UMN of CN VII are bilateral, however, the LMN are unilateral. Thus, the main distinction between an UMN and LMN lesion is that in the former, there is hemiplegia of the contralateral mid- and lower-face, whereas in the latter, there is complete hemiplegia of the ipsilateral face.

Question 22

Where do UMNs for cranial nerve nuclei descend?

Answer 22

Anterior to the corticospinal tract

Question 23

What nerves receive no direct corticobulbar innervation?

Answer 23

CN 3, 4, 6. So specific collections of neurons in the brainstem control the movements of them.

Question 24

What makes up large MNs? Small MNs?

Answer 24

Large MN - FF-Unit

Small MN - S-Unit

Question 25

What are the parts of the internal capsule?

Answer 25

Anterior Limb
Genu
Posterior Limb

Question 26

Describe LMN Syndrome.

Answer 26

Muscles become weak and atrophic. Sometimes twitches in the muscles may develop as well.

Caused as a result of damaged anterior horn cells.

Question 27

Describe UMN Syndrome.

Answer 27

Damaged UMNs, often caused by stroke. Muscles become stiffened and atrophic after time, but no twitches develop.

Question 28

Damage to what systems will not result in weakness?

Answer 28

Cerebellum
Association Cortex
Basal Ganglia