Located in the hypothalamus, the SCN is a tiny group of nerve cells that receives information about light levels from the eyes. This information helps the SCN to regulate the body's natural sleep-wake cycle, also known as the circadian rhythm.

Here's a breakdown of why the SCN is considered the biological clock:

* Light sensitivity: The SCN receives input from specialized cells in the retina that are sensitive to light, particularly blue light. This input helps the SCN to synchronize its rhythm with the day-night cycle.

* Circadian rhythm regulation: The SCN acts as a pacemaker, generating a rhythm of electrical and chemical activity that oscillates approximately every 24 hours. This rhythm influences the release of hormones like melatonin, which promotes sleep, and cortisol, which promotes wakefulness.

* Influence on bodily functions: The SCN's rhythmic activity extends beyond sleep-wake cycles, affecting various physiological processes like body temperature, hormone secretion, and even cell regeneration.

Essentially, the SCN acts as a master conductor, orchestrating the rhythm of various bodily functions, keeping them in sync with the natural environment.