UMN vs. LMN Lesions Part 2

Flashcards covering the distinctions between upper and lower motor neuron lesions in veterinary neurology, including definitions, anatomical locations, and clinical signs.

What structures are included in the Upper Motor Neuron (UMN)?

The Brain and Spinal cord.

What components make up the Lower Motor Neuron (LMN)?

Peripheral nerves, neuromuscular junction, and muscle.

What is the general physiological outcome of an Upper Motor Neuron (UMN) lesion?

Loss of inhibition.

What is the general physiological outcome of a Lower Motor Neuron (LMN) lesion?

Loss of function.

How is paresis defined in canine and feline neurology?

Abnormal gait generation (UMN) or the inability to bear weight (LMN).

What is the definition of paralysis?

Loss of voluntary movement.

What is the definition of ataxia?

Disordered movement and loss of proprioception or postural reactions.

What distinguishes a reflex from a reaction?

Reflex → is an immediate motor response to sensory input not requiring higher integration from the brain (patellar reflex)

Reaction → requires conscious or unconscious cerebral integration (menace response)

What is nociception, and what is its alternative name?

Also known as “deep pain,” it is a conscious reaction to noxious stimuli, distinct from the withdrawal reflex.

How does muscle tone differ between UMN and LMN lesions?

UMN lesions → hypertonia

LMN lesions → hypo- or atonia

How do spinal reflexes differ between UMN and LMN lesions?

UMN lesions result in normal to hyperreflexia, while LMN lesions result in hypo- or areflexia.

Compare the gait characteristics of UMN vs. LMN dysfunction.

UMN gait involves delayed generation and long-strided movements; LMN gait involves weak, short-strided movements and an inability to support weight.

Under what condition does neurogenic atrophy occur in LMN lesions?

If the lesion persists for more than $7\,d$.

Which spinal segments comprise the ventral branches of the brachial plexus?

$C6-T1(2)$.

Which spinal segments comprise the ventral branches of the lumbosacral plexus?

$L4-S3$.

What types of paralysis are characteristic of UMN versus LMN lesions?

UMN lesions cause spastic paresis/paralysis, while LMN lesions cause flaccid paresis/paralysis.

How do postural reactions/proprioception findings differ between UMN and LMN lesions?

They are abnormal or absent in UMN lesions, whereas they are typically normal in LMN lesions unless the lesion is severe.