Upper and Lower Motor Neurons

Question 1

Variations in muscle tone

Answer 1

-variations in muscle tone are noted with the degeneration of the reflex center of the spinal cord
>a decrease in muscle tone (flaccid limbs) is noted with damage to the lower motor neurons (LMN)
>a increase in muscle tone (rigid limbs) is noted with damage to upper motor neurons (UMN)

Question 2

Motor neurons within CNS

Answer 2

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

Question 3

Motor neurons role

Answer 3

-responsible for controlling somatic and autonomic functions

Question 4

Neuromuscular junctions

Answer 4

-motor neurons form specialized synapses onto muscle fibers in periphery

Question 5

Types of motor neurons

Answer 5

1.Upper motor neurons (UMN)
2.Lower motor neurons (LMN)

Question 6

Upper motor neurons

Answer 6

-motor neurons that have cell bodies within the motor cortex of the brain (cerebrum, midbrain, pons, medulla), and have axons extending through the CNS that synapse on LMN
**they control or regulate the movements of LMNs

Question 7

Lower motor neurons

Answer 7

-motor neurons within the CNS (brainstem, cranial nerves except 1,2,8, and the spinal cord) that have axons extending into the PNS to innervate targets

Question 8

Sub types of Lower motor neurons

Answer 8

-alpha
-beta
-gamma

Question 9

Clinical Signs of Lower motor neuron damage

Answer 9

**signs seen at level of lesion
1. paresis (partial loss of motor function) or paralysis (complete loss) = flaccid
2. decreased or absent muscle tone
3. muscle atrophy (quite quickly)
4. decreased or loss of local reflexes

Question 10

Clinical signs of upper motor neuron damage

Answer 10

**signs seen caudal to lesion
1. paresis or paralysis
2. increased or normal muscle tone
3. muscle atrophy (will take much longer)
4. increased or normal local reflexes

Question 11

Functional Segments

Answer 11

-Brain and Brainstem- all 4 limbs affected in same way
-C1-C5 (all 4 limbs affected in same way)
-C6-T2 (brachioplexus- LMN signs to thoracic limbs; UMN signs to pelvic limbs)
-T3-L3 (Thoracic limbs normal; pelvic limbs with UMN signs)
-L4-S2 (lumbosacral plexus- thoracic limbs normal; pelvic limbs LMN signs)
-Caudal (cauda equina)- Possibly LMN to tail and pelvic limbs + perineum