Humans, like all mammals, have a 24 hour biological clock Remains despite lack Of environmental cues the time of
If people are placed in an environment /wo any access to daylight, they follow an activity/rest cycle of about 24.5
Can differ between people and lead to different patterns of wakefulness and alertness. Change as a function of age.
Circadian rhythms are controlled by the suprachiasmatic nucleus (part of the hypothalamus) and located above the optic chiasm.
Light resets the SCN via a small branch of the optic nerve known as the retinohypothalamic pathway.
Damage to the SCN results in less consistent body rhythms that are no longer synchronized to environmental patterns of light/dark.
Light → retina → optic nerve (retinohypothalamic pathway) → hypothalamus (suprachiasmatic nuclei) → ↑ arousal state;
Melatonin
Melatonin is produced by the pineal gland and promotes sleep.
Its production is inhibited by light and therefore its levels begin to rise once light levels of the day begin to decrease.
Melatonin levels decrease /w age.
It is believed that melatonin feeds back to help reset the biological clock through its effects on receptors in the CNS