Final answer:
True, the hypothalamus plays a significant role in maintaining circadian rhythms by responding to environmental signals and regulating the secretion of hormones like melatonin.
Step-by-step explanation:
The statement that the hypothalamus has a major role in maintaining circadian rhythms is True. The hypothalamus, located below the thalamus, is integral in controlling various body functions, including hormonal regulation, body temperature, and circadian rhythms—sometimes referred to as sleep cycles. Circadian rhythms are the physical, mental, and behavioral changes that follow a roughly 24-hour cycle, responding primarily to light and darkness in an organism's environment. The hypothalamus responds to a variety of signals, such as light exposure, which influences the secretion of melatonin by the pineal gland to regulate sleep-wake cycles. In essence, the hypothalamus acts as a coordinator for a myriad of physiological processes, one of which is the synchronization of the body's biological clock with environmental cues, playing a crucial part in maintaining the body's homeostasis.