Between week six and ten, fetal bodies burst into motion, achieving graceful, stretching, and rotational movements of the head, arms and legs. Movement is spontaneous, endogenous, and typically cycles between activity and rest. Breathing movements and jaw movements have begun. Hands are busy interacting with other parts of the body and with the umbilical cord. From this early stage onward, movement is a primary activity, sometimes begun spontaneously, sometimes provoked by events.
Spontaneous movement occurs earliest, probably expressing purely individual interests and needs.
Evoked movement reflects sensitivity to the environment. For example, between 10 and 15 weeks g.a., when a mother laughs or coughs, her fetus moves within seconds. The vestibular system, designed to register head and body motion as well as the pull of gravity begins developing at about 8 weeks. This requires construction of six semicircular canals, fluid-filled structures in the ears, which are sensitive to angular acceleration and deceleration, and help maintain balance. Tasting and Smelling The structures for tasting are available at about 14 weeks g.a. and experts believe that tasting begins at that time.