Motor Neurons

Question 1

Fasciculations are associated with which lesion type? (UMN or LMN)

Answer 1

LMN

Question 2

What are common conditions that cause LMN syndrome?

Answer 2

1. peripheral nerve, spinal nerve, or cranial nerve lesions 2. Cauda equina lesions 3. Strokes or tumors affecting alpha motor neurons in ventral horn or brainstem 4. Polio (viral infection of alpha-motor neurons) 5. ALS 6. Guillain-Barre (demyelinating disease) 7. Werdnig-Hoffman disease (degeneration of anterior horn)

Question 3

Common characteristics of LMN syndrome

Answer 3

muscle weakness decreased reflexes decreased muscle tone

Question 4

Common characteristics of UMN syndrome

Answer 4

hypertonicity and spacticity

Question 5

What is spinal muscle atrophy

Answer 5

-group of diseases caused by degeneration of the anterior horns -progressive -begin in infancy -due to abnormalities in chromosome 5 -motor neurons are affected in the spinal cord and cranial motor nuclei

Question 6

What are UMNs and their relationship to LMNs?

Answer 6

UMNs all neurons that constitute descending pathways that control LMNs in brainstem and spinal cord.

Question 7

Which tract is the only

• descending pathway to project DIRECTLY to alpha-motor neurons of distal muscles
• generate FINE movements of the fingers?

Answer 7

corticospinal tract

primary pathway for goal-directed movements

Question 8

Where does the CST originate?

Answer 8

primary motor cortex (area 4) and premotor & somatosensory cortex

NB: Betx cells = pyramidal neurons (level 5 of cortex)

Question 9

What is the internal capsule and what is its involvment in CST?

Answer 9

• white matter pathway, through which the CST travels (POSTERIOR limb)
• pyramidal decussation: for Lateral CST (crossed)
• Anterior CST remains uncrossed

Question 10

Compare and contrast LCST vs ACST

Answer 10

• LCST projects directly and indirectly to motor neurons and motor interneurons in lateral ventral horn to distal muscles
• ACST projects bilaterally to motor neurons and interneurons in medial ventral horn (to proximal and trunk muscles)

Question 11

LCST Pathway

Answer 11

Question 12

ACST Pathway

Answer 12

Question 13

Which are affected more in posturing/spacticity: flexors or extensors?

Answer 13

Upper limb: Flexors (more than extensors)

Lower limb: Extensors (more than flexors)

Question 14

Positive Hoffmans

Answer 14

Reflex test of UMN syndrome: if thumb flexes and adducts –> positive Hoffman

Question 15

What “sided” is corticobilbar tract innervation mostly? (ipsilateral/contralateral/bilateral)

Answer 15

bilateral mostly, except:

1. Except: contralateral to CNVII to lower nucleus of VII (these go to lower face)
2. Mostly contralateral to CN XII (motor neurons to the tongue)

Question 16

What is the paralysis expereinced with lesions to one corticobulbar tract?

Answer 16

1. Paralysis to contralateral lower face
2. Some paralysis to opposite tongue and difficulty swallowing

Question 17

How is CN VII tested?

Answer 17

Upper n: close eye or raise eyebrows

Lower n: retract mouth

Question 18

What is seen in Bell’s palsy?

Answer 18

• LMN paralysis of 1/2 of face
• Both upper and lower face affected on affected side

Question 19

What is the “sidedness” of innervation for the face?

Answer 19

Upper face: bilateral

Lower face: contralateral only