What is known as the pacemaker for mammalian circadian rhythms?

The Suprachiasmatic Nucleus (SCN) is recognized as the primary pacemaker for mammalian circadian rhythms. It is a small group of neurons located in the hypothalamus that plays a crucial role in regulating the body's internal clock. The SCN responds to environmental light cues through retinal projections, which helps to synchronize circadian rhythms with the external light-dark cycle, thus influencing sleep-wake patterns, hormone release, and various physiological processes.

In addition to its function as the main pacemaker, the SCN also coordinates the timing of circadian rhythms throughout the body by signaling other brain regions and peripheral tissues. Its ability to regulate these rhythms is vital for maintaining overall health and well-being, as disturbances in circadian rhythms can lead to sleep disorders, metabolic issues, and other health problems.

Other parts of the brain, such as the pineal gland, hypothalamus, and thalamus, have roles related to circadian rhythms or overall brain function but do not serve as the primary pacemaker. For instance, while the pineal gland produces melatonin in response to signals from the SCN, it does not initiate the regulation of the circadian rhythm itself. Similarly, the hypothalamus houses the SCN but is not