Lecture 10 9/6/23 Flashcards
Where does the upper motor neuron have its origin/cell body?
in the brain
Where do the lower motor neurons have their origins/cell bodies?
in the spinal cord
What is a spinal cord intumescence?
a “swelling” of the spinal cord that enlarges the spinal cord to contain the LMN cell bodies
Where is the cervical-thoracic intumescence?
C6-T2
Where is the lumbo-sacral intumescence?
L4-S3
What are the signs of a lower motor neuron lesion?
-paresis or paralysis
-weak or absent spinal reflexes
-decreased muscle tone
-rapid, severe neurogenic atrophy
What is muscle tone?
the ability to prevent passive stretch of the muscle
Why is paralysis associated with LMN termed “flaccid” paralysis?
decreased muscle tone makes animal “floppy”
How do paresis and paralysis differ?
-paresis is a weakness, which can vary in severity
-paralysis is total loss of movement
Why do the spinal reflexes weaken/disappear with LMN lesions?
because the lesion is within the reflex arc that allows the reflex to normally occur
What are the two types of paresis?
-ambulatory: weak but walking independently
-nonambulatory: some movement, but not walking independently
How do paraplegia and tetraplegia differ?
paraplegia: paralysis of hind limbs only
tetraplegia: paralysis of all limbs
What is a shriveled muscle a sign of?
denervation atrophy
Which reflex maintains muscle tone?
muscle stretch reflex
What causes denervation atrophy?
-under normal conditions, small amounts of acetylcholine are released even when muscle is not contracting
-denervation leads to loss of acetylcholine release
-lack of acetylcholine release causes muscle to atrophy quickly
What are the signs of an upper motor neuron lesion?
-paresis or paralysis
-normal or increased spinal reflexes
-normal or increased muscle tone
-mild disuse atrophy
Why is paralysis caused by UMN lesions known as “spastic” paralysis?
rigid muscle tone associated with UMN lesions leads to animal being paralyzed with contracted muscles
Why are muscle tone and spinal reflexes increased with UMN lesions?
-under normal circumstances, UMN restricts the spinal reflexes of the LMN so that they are not exaggerated
-UMN lesions prevent this restriction and allow reflexes to be “full strength”
What is clonus?
exaggerated patellar reflex caused by UMN; lower limb vibrates after reflex
What is the crossed extensor reflex?
when testing the withdrawal reflex, the opposite limb will extend despite animal being recumbent
