Introduction to Upper and Lower Motor Neuron Lesions

Summary

This video explores motor disorders, focusing on the differences between upper and lower motor neuron lesions. It covers the pathways of voluntary movement, the pyramidal system, and the anatomy of motor control from the brain to skeletal muscles. The video also discusses the clinical signs and causes of upper and lower motor neuron lesions, including strokes, infections, and spinal cord injuries. Additionally, it touches on other motor disorders such as skeletal muscle diseases, electrolyte imbalances, and neuromuscular junction disorders like myasthenia gravis and botulism, offering a comprehensive understanding of these conditions.

Takeaways

• 😀 Upper motor neuron lesions occur when there is damage to the brain, brainstem, or spinal cord affecting voluntary muscle movement.
• 😀 Lower motor neuron lesions happen when there is damage to the spinal cord or brainstem affecting the transmission of signals to skeletal muscles.
• 😀 The pyramidal system, which is crucial for voluntary movement, involves the transmission of signals from the brain to the spinal cord via upper motor neurons and from the spinal cord to muscles via lower motor neurons.
• 😀 Most upper motor neurons travel through the lateral corticospinal tract, crossing over at the medulla to control the opposite side of the body.
• 😀 The anterior corticospinal tract helps control proximal muscles and crosses over at the level of the spinal cord.
• 😀 The rubrospinal tract, originating from the red nucleus in the midbrain, influences muscle flexion and inhibits muscle extension.
• 😀 Upper motor neuron damage leads to minimal muscle atrophy but hyperreflexia, including exaggerated deep tendon reflexes like the patellar reflex.
• 😀 Lower motor neuron damage results in muscle atrophy, flaccid paralysis, absent tendon reflexes, and possible fasciculations (muscle twitches).
• 😀 The Babinski sign, where the toes fan out and dorsiflex when the sole is scraped, is a hallmark of upper motor neuron lesions.
• 😀 Disorders of skeletal muscles or neuromuscular junctions, such as necrotizing myopathies or myasthenia gravis, can also lead to motor dysfunctions.
• 😀 A neurological exam can help distinguish between upper and lower motor neuron lesions, guiding proper diagnosis and treatment.

Q & A

What are motor disorders, and how are they classified?

Motor disorders are conditions where the normal functioning of skeletal muscles is affected, especially those muscles under voluntary control. These disorders are often categorized based on whether they involve upper or lower motor neurons.

What is the pyramidal system and its role in voluntary movement?

The pyramidal system is a motor pathway responsible for voluntary movement. It involves the transmission of signals from the brain, through the brainstem or spinal cord, and to the skeletal muscles, using upper motor neurons to communicate with lower motor neurons.

How do upper motor neurons communicate with lower motor neurons?

Upper motor neurons transmit signals from the brain to the spinal cord or brainstem. These signals then synapse with lower motor neurons, which extend to the skeletal muscles to initiate movement.

What happens to motor function when there is an upper motor neuron lesion?

An upper motor neuron lesion typically results in minimal muscle atrophy, weakness, hyperreflexia (exaggerated reflexes), and a positive Babinski sign (dorsiflexion and fanning of toes when the sole is scraped).

What is the Babinski sign, and what does its presence indicate?

The Babinski sign occurs when the sole of the foot is scraped, causing dorsiflexion and fanning of the toes. It is a sign of upper motor neuron damage and suggests a lesion in the brain or spinal cord.

What are the differences between upper and lower motor neuron lesions in terms of muscle atrophy?

In upper motor neuron lesions, muscle atrophy is minimal because other neurons can compensate. In lower motor neuron lesions, muscle atrophy is more pronounced since the neurons that directly stimulate the muscles are damaged.

How do reflexes differ in cases of upper and lower motor neuron lesions?

In upper motor neuron lesions, deep tendon reflexes are hyperreflexive, while superficial reflexes are diminished or absent. In lower motor neuron lesions, reflexes are typically absent, and muscle fasciculations may be present.

What is the role of the rubrospinal tract in motor control?

The rubrospinal tract originates in the red nucleus of the midbrain, and it facilitates muscle flexion while inhibiting muscle extension by targeting lower motor neurons in the spinal cord.

What are common causes of upper motor neuron lesions?

Common causes of upper motor neuron lesions include brain injuries such as strokes, infections, or tumors, and damage to the brainstem or spinal cord, particularly the white matter of the spinal cord where upper motor neurons travel.

What causes lower motor neuron lesions, and where do they typically occur?

Lower motor neuron lesions can occur due to damage to the spinal cord, particularly the anterior horn or the axons leaving the spinal cord. Conditions such as spinal cord injury or diseases affecting the ventral gray matter can result in lower motor neuron lesions.