Motor System

Question 1

An UPPER MOTOR LESION of CN 7 will cause what?

What is a likely cause of this lesion?

Answer 1

contralateral paralysis of the LOWER face
(upper face spared)

• STROKE

Question 2

A LOWER MOTOR LESION of CN 7 (or Cranial nuclei) will cause what? What is a likely cause of this lesion?

Answer 2

ipsilateral paralysis of UPPER & LOWER side of face –> CANNOT CLOSE EYE (orbicularis oculi is non-functioning)

• BELL’S PALSY
  so cut Cn 7 on left = left side of face wiped out (upper & lower)

Question 3

What is a motor unit?

Answer 3

Muscle fiber & everything it innervates

Question 4

What is an upper motor neuron?

Answer 4

anything above the Anterior Horn cells

but below the cerebellum, basal ganglia, and Association Cortex

Question 5

What is the size principle? What is the order of the units?

test

Answer 5

There is a proportional increase in the muscle contraction

• LMN’s are recruited in order of size & force**
  SS - FR - FF

Question 6

Where does the Lateral Corticospinal tract located in the internal capsule? Where is the corticobulbar tract in the internal capsule?

(TEST)

Answer 6

1. Posterior Limb of the INTERNAL CAPSULE (PL)

2. GENU = Corticobulbar

Question 7

Where does the CST originate from?

Answer 7

1. Motor cortex
2. Adjacent areas
3. Sensory cortex (somatosensory)

Question 8

Where does the CST terminate?

Answer 8

1. SPINAL CORD (anterior horn cells)
2. BRAINSTEM
3. Association cortex
   - Basal ganglia, thalamus, RT, sensory nuclei

Question 9

Where is the Corticobulbar tract in the internal capsule?

Answer 9

GENU of the internal capsule (the bend)

Question 10

Where does the Corticobulbar tract terminate? (2 areas)

Answer 10

• terminates on INTERNEURONS of the RETICULAR FORMATION

- some on SPINAL MOTOR NEURONS

Question 11

Which Cranial nerves does the Corticobulbar tract innervate? Which does it NOT innervate?

Answer 11

1. 5,7,9,10,12

5 & 12 have more contralateral contribution (so opposite would be affected?)

2. CN 3,4,6 of the eye are NOT innervated by Corticobulbar tract

Question 12

What structures are innervated by the MEDIAL column of the LMN of the spinal cord? LATERAL?

What is dorsally places? Ventrally?

Answer 12

1. AXIAL (leg/trunk)
2. ARM - distal limb muscles
   = SOMATOTOPIC org.

• DORSAL = flexor
• VENTRAL = extensor

Question 13

What do LMN’s release?

Answer 13

acetylcholine

Question 14

What are corticospinal/corticobulbar neurons referred as?

Answer 14

UPPER MOTOR NEURON

Question 15

What are neurons of the brainstem & spinal cord?

Answer 15

LOWER MOTOR NEURONS

Question 16

Distinguish between the following three muscle units:

Answer 16

1. S-units
   - slow twitch
   - ALOT of mitochondria & capillaries
   - not fatigueable
   - small force
   - RED MUSCLE fibers
2. FR-units
   - fast twitch
   - WHITE fibers
   - moderate force
   - fatigue resistant
3. FF-units (only fatiguable unit)
   - fast twitch
   - WHITE fibers
   - LARGE force
   - fatigueable***

Question 17

LMN’s are found in the white matter or the grey matter of the spinal cord? Which areas of the spinal cord have grey matter enlargement?

Answer 17

GREY MATTER

• CERVICAL (arm) & LUMBOSACRAL (leg)

Question 18

What is the firing pattern of LMN’s dependent on?

Answer 18

INTERNEURONS

Question 19

What is the transmitter in Corticospinal tract? Is it excitatory or inhibitory?

Answer 19

1. GLUTAMATE

2. Excitatory

Question 20

What are the 3 control systems for LMN’s?

Answer 20

1. Descending Pathway
2. Higher cortical centers
3. Basal Ganglia & Cerebellum**

Question 21

Fibers in the CST are JUST localized in the MOTOR cortex. TRUE OR FALSE?

Answer 21

FALSE

• they are in adjacent cortex & sensory cortex as well

Question 22

Where does the CST originate from?

Answer 22

1. Primary motor cortex
2. Adjacent Frontal Motor
3. Parietal areas
   (somatosensory)

Question 23

CST descends through what?

Answer 23

POSTERIOR LIMB of the Internal Capsule

Question 24

If you lesion the PL, will this lead to ipsilateral loss or contralateral loss? What tract will be affected if you lesion the GENU of the internal capsule?

Answer 24

1. CST in PL (fine motion)
   - CONTRALATERAL loss

(this is similar to a stroke)

2. Corticobulbar Tract

Question 25

Where does the CST decussate?

Answer 25

Medullary Pyramids - most fibers = LATERAL corticospinal tract*

Question 26

What will occur if you lesion a PYRAMID before the CST crosses? What about a lesion in the spinal cord?

Answer 26

PYRAMID = OPPOSITE SIDE SPINAL CORD = same side*** (fine motor movement affected)

Question 27

If you lesion the cerebellum, association cortex, or basal ganglia, will there be WEAKNESS?

Answer 27

NO -

Question 28

Weakness only occurs in lesion of which 2 neurons?

Answer 28

UPPER MOTOR NEURONS + LOWER MOTOR NEURONS (anterior horn cells)

Question 29

What are the symptoms of a LOWER MOTOR NEURON lesion?

Answer 29

1. Flaccid paralysis 2. Hyporeflexivity 3. Fasciculations * ATROPHY

Question 30

What are the symptoms of an UPPER MOTOR NEURON lesion?

Answer 30

1. Spasticity 2. Exaggerated reflexes 3. Hemiplegia -STROKE!!!

Question 31

The motor neurons of Cranial nerves, sensory relay nuclei, & RT is which tract?

Answer 31

CORTICOBULBAR - anterior to CST tract

Question 32

Where does the cortibulbar tract end?

Answer 32

Interneurons of the RETICULAR FORMATION

Question 33

Which nerves receive no direct corticobulbar innervation?

Answer 33

3,4,6 | controlled instead by MLF

Question 34

A contralateral loss of the RIGHT lower face muscles would be indicative of what?

Answer 34

``` LEFT STROKE (or lesion of the cortex) CN 7 ```

Question 35

An ipsilateral loss of the whole LEFT face would be indicative of what?

Answer 35

Bell's Palsy | lesion CN7 or the nucleus

Question 36

What modulates the motor cortex?

Answer 36

1. Association Cortex 2. Basal Ganglia 3. Cerebellum (modulate via UPPER MOTOR NEURONS)