2.24.25 lecture: paralysis

can a neuron with a damaged axon have an action potential? can it release neurotransmitter?

yes; no

name the 2 types of paralysis

flaccid and spastic

is this a symptom of flaccid or spastic paralysis:

muscles can be simulated by reflex activity

spastic

is this a symptom of flaccid or spastic paralysis:

muscle atrophy

flaccid

remember, atrophy means loss of muscle tone

is this a symptom of flaccid or spastic paralysis:

no reflex activity

flaccid

is this a symptom of flaccid or spastic paralysis:

no voluntary control of muscles

both

is this a symptom of flaccid or spastic paralysis:

muscle atrophy is delayed

spastic

____________ is what separates spastic and flaccid paralysis

reflex activity

what causes flaccid paralysis?

damage to LOWER motor neuron

what causes spastic paralysis?

damage to UPPER motor neuron

what does damage to the upper motor neuron result in?

spastic paralysis

what does damage to the lower motor neuron result in?

flaccid paralysis

Why does injury to lower motor neurons (LMNs) cause flaccid paralysis?

LMNs are the final pathway for transmitting signals from the CNS to the muscles, so when damaged, the muscles lose all input

what eventually happens when you get flaccid paralysis?

eventually, that LMN axon dies, leaving nothing to innervate that simulate that skeletal muscle, therefore no way to even have reflex activity

why would a person with a spinal chord injury still have a patellar-tendon reflex?

because they have spastic paralysis and the LMN is still in tact.

"okay but the UMN is damaged, why is the LMN doing anything?" you may ask regarding spastic paralysis

remember that reflex activity is processed in the spinal chord, so if the LMN is intact, and there's an injury to the spinal chord above it, the section of chord associated with the intact LMN will still be able to internally process reflex at that level, it just won't be regulated by an UMN because its access to the cerebrum is cut off

so why does atrophy not happen as quickly with spastic paralysis?

because the muscle is still innervated by a healthy LMN that can continue to stimulate the muscle

Why does injury to upper motor neurons (UMNs) cause spastic paralysis?

UMNs normally control and regulate LMNs in the spinal cord. When UMNs are damaged, the LMNs lose proper regulation, leading to spasticity and exaggerated reflexes.