UMN and LMN Lesion

What is an upper motor neuron

A neruon that originates in the brain and travels down to synapse with lower motor neurons in the spinal cord or brainstem.

What is a lower motor neuron

A neruon that travels from the spinal cord or brainstem directly to the muscle.

Where does an UMN lesion occur

Above the ant horn cell in the spinal cord, or above cranial nerve motor nuceli

Where does a LMN lesion occur

At the ant horn cell, nerve root, peripheral nerve, or neruomuscular junction.

Describe the atrophy seen in LMN lesion and why

Large atrophy due to deinnervation.

Describe the atrophy seen in UMN lesion

Minimal atrophy seen due to lack of use.

What type of weakness is seen in UMN lesion

Spastic paralysis, and extra-pyramidal pattern of: extensors are weaker than flexors in the arms and vice versa in legs.

What type of weakness in seen in LMN lesion

Flaccid paralysis.

What type of tone is seen in UMN lesion

Hypertonia due to increased activity of the alpha motor neuron.

What happens to DTR in UMN lesion

Hyperreflexia

What happens to DTR in LMN lesion and why

Reduced or absent due to decreased gamma motor neuron activity.

Are fasiculations seen with LMN lesion

Yes

Are fasiculations seen with UMN lesion

No

What special tests are present with UMN lesion

Babinski/hoffmans
Pronator drift
Clonus

What is clonus and when is it seen

Series of involuntary, rythemic muscle contractions caused by a sudden sustained stretching of a muscle. Seen with UMN lesions.