Summary
Highlights
The video introduces upper and lower motor neuron lesions. Upper motor neurons are located in the brain or brainstem, with their axons extending down the spinal cord to synapse with lower motor neurons. Lower motor neurons are located in the ventral horn of the spinal cord and their axons extend to innervate skeletal muscles.
Upper motor neuron lesions are characterized by 'hyper' prefixes. They include hypertonicity (increased muscle tone), hyperreflexia (increased muscle reflexes), and spasticity (muscle tightness). This occurs because the upper motor neuron, which normally regulates the lower motor neuron, is damaged, leading to unregulated and overactive lower motor neuron activity. Other characteristics include disuse atrophy and no fasciculations.
Lower motor neuron lesions are characterized by 'hypo' prefixes. They include hypotonia (decreased muscle tone), hyporeflexia (decreased muscle reflexes), and flaccidity. This is due to damage to the lower motor neuron or its axon, preventing it from properly innervating muscle. Other characteristics include denervation atrophy and fasciculations (involuntary muscle twitching) due to random impulses.
Both upper and lower motor neuron lesions cause weakness, so this symptom does not differentiate them. The Babinski sign is a diagnostic test for upper motor neuron lesions. A normal response (negative Babinski) is toes pointing downward. A positive Babinski sign, indicative of an UMNL, occurs when the toes point upward and fan out upon stimulation.
To remember UMNL, think 'Up' or 'Hyper': more muscle contraction (spasticity), more tone (hypertonicity), more reflexes (hyperreflexia), disuse atrophy, and a positive Babinski sign (toes point up). For LMNL, think 'Lower' or 'Hypo': less muscle contraction (flaccidity), less tone (hypotonia), less reflexes (hyporeflexia), denervation atrophy, and a negative Babinski sign (toes point down).