Intro: UMN vs LMN Flashcards
LMN & UMN are
a set of tracts or nerves & nuclei that form a clinically recognizable functional unit
LMN consist of parts of the NS that when injured
Decrease the strength of the Muscle Stretch Reflex (MSR)
UMN consist of parts of the NS that when injured
Increase the strength of the Muscle Stretch Reflex (MSR)
Reflex sign of a LMN lesion
Hypo-reflexia
Reflex sign of a UMN lesion
Hyper-reflexia
Tone sign of a LMN lesion
Hypotonia
Will a patient have fasciculation and fibrillation w/ LMN lesion?
Yes
Will a patient demonstrate weakness from a LMN lesion?
Yes, from decreased innervation
Will a patient demonstrate atrophy of the muscles from a LMN lesion?
Yes
Tone sign of a UMN lesion
Hypertonia
Will a patient have fasciculation and fibrillation w/ UMN lesion?
No
Will a patient demonstrate weakness from a UMN lesion?
Yes - from disuse
Will a patient demonstrate atrophy of the muscles from a UMN lesion?
No
A good indication of whether a patient has a UMN or LMN injury
LMN: Individual muscles may be affected
UMN: Muscles always affected in groups, never individual muscles
2 Abnormal UMN Reflexes
Babinski’s
Clonus
Clonus
An involuntary, repetitive, rhythmic contraction of a muscle when held in a stretched state. Initiated in the spinal cord.
Is usually a sign of damage to the nerve tracts above the place where the stretch reflex is initiated
What is muscle tone?
Tone is the resistance of muscles to passive stretch or elongation
What is the purpose of normal tone?
Normal tone resists the effects of gravity in posture and movement, yet is low enough to allow free movement.
Spasticity
A velocity dependent increase in resistance to passive movement. The faster the passive movement the stronger the resistance. It’s an involuntary muscle contraction. Measured on the Modified Ashworth Scale
Rigidity
A non velocity dependent increase in resistance to passive movement
Fasciculations
A LMN sign
Visible, coordinated twitches among the muscle fibers. The earliest objective sign of muscle denervation.
Caused by spontaneous APs generated after injury to the axon.
Fibrillations
LMN sign
Small, non-visible uncoordinated contractions among the muscle fibers.
Cause: As axon degenerates further, motor units are no longer joined by a functioning axon so muscle fibers do not contract as a unit
