Upper Motor Neurons

Question 1

UMN syndrome signs

Answer 1

Muscle weakness
Increased muscle tone 
Exaggerated deep tendon reflexes
Decreased cut. abdominal reflexes 
Clonus 
Synkinesia

Question 2

Corticospinal tract origins

Answer 2

> 50% from primary motor cortex (Brodmann area 4)

Premotor and supplementary motor areas (Brodmann area 6)

Parietal lobe (Brodmann areas 3,1,2,5,7)

Question 3

Type of fibers which innervate the cranial nerves (crossed and uncrossed)

Answer 3

All cranial nerves are innervates by crossed and uncrossed fibers

Expect facial nerve:
- upper muscles innervation by crossed and uncrossed fibers

• lower muscles innervation by crossed fibers

Question 4

Pattern of UMN muscle weakness

Origin of the lesion
(Where are the weaknesses)
(How do they look like)

Answer 4

• Is a central lesion
• where the weaknesses are:
  In UE: extensors are weaker than flexors
  In LE: flexors are weaker than extensors
• looks like: pronator drift

Question 5

What type of motor neurons are responsible for the tone of resting muscles?

Answer 5

Gamma motor neurons (their cell bodies are in the anterior horn of the spinal cord)

Question 6

Types of hypertonia

Answer 6

Extrapyramidal rigidity (from basal ganglia)

Spasticity (from corticospinal pathways)

Question 7

Describe extrapyramidal rigidity

Answer 7

At basal ganglia level
Not depended on speed
Are bidirectional

Increased muscle tone to passive movements, going in all directions

Rigidity from beginning to end of movement (=lead pipe rigidity)

Cogwheel rigidity (seen in Parkinson’disease)

May include plasticity (=newly places d limb stays in same position)

Question 8

Describe spasticity

Answer 8

Lesions are in corticospinal pathway
Depends on speed, is unidirectional

The faster the movement, the higher the resistance. Slow movement, fewer resistant

Clasp knife phenomenon: at extreme range of motion, muscle tone suddenly decreases

Question 9

Why exaggerated deep tendon reflexes occur in UMN disorders?

Answer 9

Hyperreflexia is associated with descending motor pathways from cortex up to the brainstem.

The reflex threshold is increased.

Includes the typical postures of muscle weakness.

Question 10

Which spinal nerves roots are involved in the diminished cut. abdominal reflexes?

Answer 10

Spinal nerve roots T8 - T10

Question 11

What is a spinal shock?

Answer 11

A sudden lesion of the spinal cord, which will affect the corticospinal pathway.

This causes initially a period of flaccidity and areflexia.

It is also accompanied by paralysis below the level of the lesion.

Question 12

What is diaschisis?

Answer 12

An acute, sudden cerebral lesion, which causes flaccid paralysis and areflexia on the opposite side of the body.
It is then soon followed by signs of UMN syndromes (spasticity and hyperreflexia)

Question 13

What are the causes of UMN syndromes?

Answer 13

• Any lesion at the corticospinal pathway
• Vascular lesions
• Inflammatory lesions
• Tumors
• Trauma
• Degenerative diseases
• Infections

Question 14

motor unit

Answer 14

consists of motor neuron and skeletal muscle fibers
group of motor unit work in groups

force, range, rate and type of movement depends on the number and size of MU recruitment

muscles are innervated according to the spinal cord segments

large muscles are innervated by 2 or more roots

Question 15

motor homunculus

Answer 15

somatotopical organization of primary motor cortex

is a cortical motor map