Motor Pathways (UMN and LMN)

Question 1

Where are the cell bodies of the LMN located?

Answer 1

found in the ventral horn of the spinal cord

&

cranial nerve motor nuclei in brain stem

Question 2

What are the target tissues of the lower motor neurones?

Answer 2

skeletal muscle

Question 3

What are 5 common symptoms of lower motor neurone lesions?

Answer 3

1. Weakness
2. Areflexia
3. Wasting
4. Hypotonia
5. Fasiculations

Question 4

Outline why the following symptoms may occur in patients with a lower motor neurone lesion:

Wasting

Hypotonia

Fasiculation

Answer 4

Wasting

loss of trophic support

Hypotonia

loss of muscle activation

Fasiculation

upregulation of muscle nAChRs to compensate for denervation

Question 5

What are the two effects of upper motor neurones on lower motor neurones?

Answer 5

Excitation of LMN

Inhibition of LMN via interneurone stimulation

Question 6

What is the overall NET effect of UMNs on LMNs?

Answer 6

overall effect is inhibitory

(therefore loss of UMN stimulation will cause an increase in LMN activity)

Question 7

What is the name of the tract carrying descending motor fibres through the spinal cord?

Answer 7

Lateral Corticospinal Tract

Question 8

At what level do the descending motor pathways decussate?

Answer 8

Medullary Pyramids

(within the medulla of the brainstem)

Question 9

Outline where the cell bodies and axons of both UMN and LMN are found within the CNS and PNS

Answer 9

UMN

cell bodies in grey (cortex) and axons in white matter of CNS

LMN

cell body grey matter (ventral horn) of CNS/spinal cord, axons located in PNS/spinal nerve

Question 10

What is a normal plantar reflex response?

Answer 10

normal

great toe plantar flexion/curl downwards

abnormal

(+ve) Babinski Sign

great toe dorsiflexion/curl upwards

Question 11

Outline the path of an upper motor neurone from the cerebral cortex to medullay pyramids

Answer 11

motor cortex (pre-central gyrus) > corona radiata > internal capsule > midbrain > pons > medullary pyramids (decussation)

Question 12

Which area of the body is innervated by the most medial aspect of the lateral corticospinal tracts?

Answer 12

Medial: arms

Middle: thorax

Lateral: legs

Question 13

Which area of the brain is supplied by the lenticulostriate arteries that can lead to pathology affecting the motor system?

Answer 13

Internal Capsule

Question 14

What area of the body is innervated by the corticonuclear projections of the nervous system?

Answer 14

Facial Muscles

(innervate the facial and neck muscles as they synapse with the lower motor neurones of the cranial nerves)

Question 15

Where are the corticonuclear/corticobulbar nuclei located?

Answer 15

brainstem

• corresponsing to the level of origin of the cranial nerves*
• (2, 2, 4, 4)*

Question 16

Why does a patient presenting with a stroke in one of the cerebral hemispheres present with forehead sparing?

Answer 16

facial motor nucleus divided in half

• upper half innervates upper facial muscles*
• lower hald innervates lower facial muscle*

upper motor nucei of facial nerve receive bilateral UMN innervation from the left and right heisphere (homunculus)

therefore loss of innervation from one hemisphere is compensated for by the contralateral innervation

Question 17

What are 4 common symptoms of upper motor neurone lesions?

Answer 17

1. Weakness
2. Hypertonia
3. Hyper-reflexia
4. Extensor Plantar Reflex (Babinski Sign)

Question 18

Why do patients with an upper motor neurone present with weakness and hypertonia?

Answer 18

Weakness

loss of the few excitatory inputs to LMN

Hypertonia

increased muscle tone due to loss of net inhibition from UMN

Question 19

How may a patient present initially following a stroke and how can does this change over time?

Answer 19

initially may present with spinal shock

once UMN activity removed the LMN activity decreases - causing weakness and hypotonia

classical symptoms then develop around 7 days later, such as hypertonia and hyper-reflexia

Question 20

Spinal Tracts Summary

Answer 20

Spinal Tracts Summary

Question 21

Answer 21