What describes the involuntary movements seen in myoclonus?

Myoclonus is characterized by sudden, involuntary muscle jerks that can occur as single or repetitive movements. These movements are abrupt and typically involve a quick contraction of a muscle or group of muscles, resulting in a jerking motion. This aligns with the description provided in the correct answer, as myoclonic jerks can appear unexpectedly and are recognized by their quick onset and termination.

The other descriptions do not fit myoclonus. Slow and purposeful movements suggest a level of control and intent that is not found with myoclonic jerks, which are involuntary. Rhythmic and repetitive movements imply a consistent pattern that can be seen in conditions like tremors, rather than the erratic nature of myoclonus. Continuous and fluid movements describe actions such as those seen in dystonia or chorea, which are also distinctly different from the quick, sporadic jerks associated with myoclonus. Therefore, the defining characteristics of sudden and jerky movements aptly describe myoclonus.