Fasciculations are seen in lesions of: September 2012
**Core Concept**
Fasciculations are involuntary muscle contractions that can be observed in the skin, underlying fascia, and muscle tissue. They are often associated with lower motor neuron lesions, which disrupt the normal communication between the central nervous system and the peripheral nervous system.
**Why the Correct Answer is Right**
Fasciculations occur due to the denervation of muscle fibers, leading to an imbalance between the excitatory and inhibitory neurotransmitters. When a lower motor neuron is damaged, the muscle fibers lose their normal inhibitory influences, resulting in spontaneous muscle contractions. This is because the denervated muscle fibers are no longer receiving the normal inhibitory signals from the lower motor neurons, leading to uncontrolled muscle contractions.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because fasciculations are not typically associated with upper motor neuron lesions, which affect the central nervous system rather than the peripheral nervous system.
**Option B:** This option is incorrect because myotonia is a condition characterized by delayed relaxation of muscles after voluntary contraction, which is different from the spontaneous contractions seen in fasciculations.
**Option C:** This option is incorrect because muscle cramps are sudden, intense contractions of a muscle or group of muscles, often caused by electrolyte imbalances or muscle fatigue, which is different from the spontaneous contractions seen in fasciculations.
**Clinical Pearl / High-Yield Fact**
Fasciculations are often seen in conditions such as amyotrophic lateral sclerosis (ALS), a progressive neurodegenerative disorder that affects both upper and lower motor neurons. The presence of fasciculations can be an important clinical sign in the diagnosis of ALS.
**Correct Answer:** A