UMN vs LMN Lecture Notes Flashcards

Flashcards based on lecture notes about Upper Motor Neurons (UMN) vs. Lower Motor Neurons (LMN).

What are Upper Motor Neurons (UMNs)?

First-order neurons responsible for carrying the electrical impulses that initiate and modulate movement.

What is the Pyramidal Tract?

Primary tract which carries signals for voluntary movement, allowing a direct pathway between the cerebral cortex and the spinal cord. It divides into the corticospinal and corticobulbar tracts.

What is the function of the anterior horn?

UMNs synapse here with LMNs to activate skeletal muscles; regulates fast and fine (skilled) movements.

What is the role of the lateral corticospinal tract?

Majority of axons decussate at the pyramidal decussation; controls distal extremities for precise, agile, and highly skilled movements.

What is the role of the anterior corticospinal tract?

About 10% of the axons do not decussate and terminate in skeletal muscles that control movements of the trunk and proximal parts of the limbs.

What are the symptoms of UMN lesions above the pyramidal decussation?

Symptoms contralateral to the lesion site.

What are the symptoms of UMN lesions below the decussation?

Symptoms ipsilateral to the lesion site.

What are the causes of UMN lesions?

Cerebrovascular accidents, traumatic brain injury, anoxic brain injury, malignancy, infections, inflammatory disorders, neurodegenerative disorders, and metabolic disorders.

What is the role of extra-pyramidal tracts?

Provide indirect pathways for the coordination of movement, maintaining posture, and regulating involuntary motor functions.

What are the tracts included in the extra-pyramidal system?

Reticulospinal, vestibulospinal, rubrospinal, and tectospinal tracts.

What are examples of injuries or diseases affecting the extra-pyramidal tracts?

Parkinson's disease (PD), Huntington's chorea (HC), multiple systemic atrophy (MSA), and progressive supranuclear palsy.

What are the clinical features of extrapyramidal tract injuries?

Hypokinesias and hyperkinesia.

What are Choreic movements?

Sudden, irregular, incomplete, aimless, variable movements.

What are Athetotic movements?

Arrhythmic, slow, exaggerated, tentacular movements.

What is Hemiballism?

Movements similar to choreic movements but much more intense and persist during sleep.

What are Hyperkinesias?

Abnormal involuntary movements that can be seen in extrapyramidal diseases.

What can bilateral injuries at the brainstem level cause?

Quadriplegia and hypertonia.

What are the characteristic symptoms of UMN lesions (upper motor neuron syndrome)?

Weakness, spasticity, clonus, hyperreflexia, Babinski sign, and Hoffman sign.

How does weakness manifest in UMN lesions?

Affects extensors of the arm and flexors of the leg.

What is the Babinski sign?

Elicited by stroking the sole of the foot; positive sign is extension of the large toe and fanning of other toes.

What is the Hoffman sign?

Babinski reflex for the upper limbs; positive sign is flexion and adduction of the thumb.

What is the function of lower motor neurons (LMNs)?

Directly innervate skeletal muscle.

What are the types of motor neurons?

Branchial, visceral, and somatic.

What are Branchial Motor Neurons?

Located in the brainstem; responsible for forming the LMNs of the cranial nerve nuclei.

What are Visceral Motor Neurons?

Component of the autonomic nervous system (ANS) and regulate smooth muscles and glands.

What are Somatic Motor Neurons?

Directly innervate skeletal muscle and relay information from the spinal cord to their target.

What are the types of somatic motor neurons?

Alpha, beta, and gamma.

What do Alpha motor neurons innervate?

Innervate extrafusal muscle fibers and are the primary means of skeletal muscle contraction.

What do Beta motor neurons innervate?

Poorly characterized, but they innervate both extrafusal and intrafusal fibers.

What do Gamma motor neurons innervate?

Innervate muscle spindles and dictate their sensitivity; fine-tune muscle contraction.

What is the presentation of LMN lesions?

Muscle atrophy, fasciculations (muscle twitching), decreased reflexes (hyporeflexia), decreased tone, negative Babinski sign, and flaccid paralysis.

What are classic examples of isolated LMN disease?

Poliomyelitis and spinal muscular atrophy.