Final answer:
Small muscle movements like fasciculations and fibrillations are involuntary twitches, whereas controlled movements involve intrinsic and extrinsic muscles of the hand and are coordinated by the cerebellum. These movements allow for complex motor tasks and are assessed through specific tests like the heel-to-shin test.
Step-by-step explanation:
Small muscle movements in the hands, fingers, feet, toes, and face are generally known as fasciculations, which refer to small, involuntary muscle twitches arising from spontaneous activity of lower motor neurons (LMNs). Another type of small muscle movement is fibrillation, which is a spontaneous muscle action potential occurring in the absence of neuromuscular input, usually resulting from LMN lesions. However, when considering purposeful and controlled small muscle movements, they are often the result of precise coordination by the cerebellum and various motor units within the muscles.
Muscles that move the wrist, hand, and fingers are powered by extrinsic and intrinsic muscles. The former originate in the forearm and the latter in the palm. These muscle groups, which include the thenar muscles on the radial aspect of the palm, the hypothenar muscles on the medial aspect of the palm, and intermediate muscles in the midpalmar region, work together for complex tasks such as typing, writing, or grasping objects through the motion known as opposition, where the thumb moves toward the fingers of the same hand.
Rapid, alternating movements are also a significant aspect of muscle control, requiring the cerebellum to coordinate movement commands and are tested via subtests such as touching each finger to the thumb and the heel-to-shin test.