Final answer:
The word derived from Greek meaning dance that refers to involuntary spasms of muscles is 'chorea.' It is related to dance only metaphorically, as the uncontrollable movements can look dance-like but are indeed involuntary and irregular.
Step-by-step explanation:
The word that is derived from Greek meaning dance and which refers to involuntary, irregular spasms of limb and facial muscles is known as chorea. Chorea comes from the Greek word "choreia", which means dance. The connection to dance is metaphorical, as the movements of someone with chorea may appear to be dance-like; however, they are involuntary and often abrupt. Chorea is part of a group of disorders called dyskinesias, which cause unintentional movements.
Contrary to skeletal muscle which is voluntary and striated, allowing controlled movements such as walking, choreic movements are not under conscious control and can disrupt normal voluntary motion. Understanding dance, with its aesthetically pleasing and controlled movements, helps to contrast the lack of control found in choreic movements. This concept also ties back to the historical significance of dance, as seen in the ancient Greek Pyrrhic dance mentioned in LibreTexts™, comprising complex and purposeful motion, unlike the spontaneous activity characterized by chorea.