What? Human behaviors that follow a 24-hour cycle. Even if you decided to live in perpetual darkness, your body would still have them! It's like your body's internal clock!

Real-world example: Think of your daily routine – you eat, sleep, and maybe even get those afternoon energy slumps all around the same time, right?

• Suprachiasmatic nuclei (SCN) = Two groups of cells in the hypothalamus, responsible for our circadian rhythms.

• SCN controls melatonin secretion by the pineal gland.

  • Melatonin Lowdown
    • Increases in the evening 🌆
    • Drops at dawn 🌅
    • Major role: Sleep-wake cycle 🛌

  Fun fact: Want to sleep like a baby? Melatonin is your best friend! High levels make you drowsy, while low levels help you wake up fresh.

• It's also a temperature controller! Melatonin drops body temperature at night.

  Real-world example: Ever felt chilly during a midnight bathroom trip? Thank melatonin!

• Melatonin affects the kidneys. Night-time means less pee production.

  Did you know?: If we're put in a constant light/dark environment, our body still follows a rhythm slightly longer than 24 hours. This shows we need to adjust our internal clocks every day to align with our environment.

Special cells in our retina sense certain light wavelengths and tell the SCN when it's dusk or dawn. This helps our body adjust melatonin levels to fit day-night cycles.

Real-world example: This is why we're told to avoid screens before bed! Screens emit the kind of light that can confuse our internal clocks.