Final answer:
Abnormal rapid muscle movements are called twitches or spasms, often associated with neuromuscular disorders or hypertonia. These twitches follow a sequence involving an action potential, calcium ion release, and cross-bridge formation leading to muscle contraction and relaxation.
Step-by-step explanation:
Abnormal movements marked by rapid contraction and relaxation of a muscle or muscle groups are called twitches or spasms. These can be a manifestation of a neuromuscular disorder, where there is an issue with the nervous control of muscle contractions. The term used to describe increased muscle tone is hypertonia, which involves hyperreflexia and can present as muscle rigidity or spasticity. During a muscle twitch, which can result from various nervous or metabolic disorders, there is a rapid movement of muscle fibers that follows a sequence of electrical and chemical events. These begin with an action potential traveling along the sarcolemma, followed by the release of calcium ions from the sarcoplasmic reticulum, and the formation of cross-bridges between the actin and myosin filaments within the sarcomeres, ultimately resulting in muscle contraction and relaxation.