11 – Upper and Lower Motor Neurons

Question 1

Variations in muscle tone are noted with:

Answer 1

-degeneration of reflex centre of spinal cord

Question 2

Decreased muscle tone (flaccid limbs) is noted with damage to:

Answer 2

-LOWER motor neurons (LMN)

Question 3

Increased muscle tone (rigid limbs) is noted with damage to:

Answer 3

-UPPER motor neurons (UMN)

Question 4

Motor neurons within the CNS:

Answer 4

-cell bodies within the grey matter
-project myelinated axons into either the CNS (tracts) or PNS (nerves)

Question 5

Motor neurons are responsible for controlling:

Answer 5

-somatic and autonomic functions

Question 6

Motor neurons form:

Answer 6

-specialized synapses onto muscle fibers in the periphery=NMJ

Question 7

Motor neurons can be classified as:

Answer 7

-UMN
-LMN

Question 8

Upper motor neurons (UMN):

Answer 8

-cell bodies within motor cortex of the brain
-axons extending through the CNS that synapse on LMN
*control or regulate movements of LMNs (mostly inhibitory)

Question 9

UMNs come from:

Answer 9

-cerebrum
-midbrain
-pons
-medulla

Question 10

Lower motor neurons (LMN):

Answer 10

-within the CNS
-have axons extending into the PNS to innervate targets

Question 11

LMNs come from:

Answer 11

-brainstem
-cranial nerves (except 1, 2, 8)
-spinal cord

Question 12

Cranial nerves 1, 2 and 8:

Answer 12

-sensory nerves only
-no motor neuron

Question 13

What are the sub-types of LMNs?

Answer 13

-alpha
-beta (hybrid of the 2)
-gamma

Question 14

What are the clinical signs of LMN damage?

Answer 14

*at the level of the lesion
1. Paresis or paralysis -> flaccid
2. Decrease or absent muscle tone
3. Muscle atrophy (relatively rapid: days)
4. Decrease or loss of local reflexes

Question 15

Paresis:

Answer 15

-can move limbs voluntarily but can’t walk
>too weak to support their limbs
*partial loss of motor function

Question 16

Paralysis:

Answer 16

*complete loss of motor function

Question 17

What are the clinical signs of UMN damage?

Answer 17

*caudal to the lesion
1. Paresis or paralysis
2. Increase or normal muscle tone
3. Muscle atrophy (slower: weeks to months)
4. Increase or normal local reflexes

Question 18

What are the functional segments of the spine?

Answer 18

1. C1-C5
2. C6-T2
3. T3-L3
4. L4-S2
5. Caudal (cauda equina)

Question 19

What would be the clinical signs to a lesion in the brain, brain stem or C1-C5?

Answer 19

-all limbs effected in same way

Question 20

What would be the clinical signs to a lesion in the C6-T2?

Answer 20

-LMN signs to thoracic limbs -UMN signs to pelvic limbs

Question 21

What would be the clinical signs to a lesion in the T3-L3?

Answer 21

-thoracic limbs=normal
-pelvic limbs=UMN signs

Question 22

What would be the clinical signs to a lesion in the L4-S2?

Answer 22

-thoracic limbs=normal
-pelvic limbs=LMN signs

Question 23

What would be the clinical signs to a lesion in the caudal (cauda equina)?

Answer 23

-possible LMN to tail and pelvic limbs (perineum)