To comprehend the mechanism of Seasonal Affective Disorder and the impact of light on our mental well-being, it's essential to grasp how our body and brain function. In this section, we'll introduce some crucial concepts to enhance our understanding.
Our brain manages a plethora of intricate bodily processes such as breathing, digestion, circulation, growth, reproduction, and repair. The brain employs two distinct systems to govern these processes: the nervous system and the endocrine system.
The nervous system is the swifter of the two. To convey messages rapidly, the brain utilizes the nervous system, which transmits brief messages, typically in mere thousandths of a second. It employs electrical impulses that travel at speeds of up to 650 feet (200 meters) per second through nerve cells.
The endocrine system communicates most messages slowly. It relies on hormones to produce longer-lasting effects. Hormonal messages are transported through the bloodstream, and it may take hours or even days for them to reach their destination and induce changes. The endocrine system consists of various ductless glands distributed throughout the body that release hormones directly into the bloodstream. These glands include the pituitary, thyroid, thymus, adrenals, pancreas, ovaries, or testes, among others. Their function is to regulate the internal environment of the entire body.
The distinction between the nervous system and endocrine system can be likened to mailing a package. To send a small item urgently, air mail or express mail is the fastest, even though it's relatively expensive and takes a few days. For larger, less urgent items, surface mail (by ship) is cost-effective, although it takes several months to reach the destination. In this analogy, air mail corresponds to the nervous system, while surface mail mirrors the endocrine system. The brain selects one of these systems based on the quantity of material and the urgency of the message it needs to convey.
Hypothalamus
The hypothalamus serves as the command center for the endocrine system. It primarily utilizes the pituitary, a pea-sized gland positioned beneath the hypothalamus, to control other glands. The hypothalamus, weighing a fraction of an ounce and approximately the size of the tip of our thumb, plays a pivotal role.
For instance, when the hypothalamus detects the need to increase the level of thyroid hormone in the blood, it dispatches a hormone to the pituitary gland, instructing it to relay the message to the thyroid gland. The pituitary promptly transmits a thyroid-stimulating hormone to the thyroid, directing it to release more thyroxin. This triggers an acceleration of metabolic rates. Similarly, the hypothalamus oversees other endocrine systems, regulating aspects such as blood sugar levels and body temperature.
Pineal Gland
The pineal gland is a minuscule, pine-cone-shaped organ located at the rear of the brain, just above the brain stem.
Many scientists regard the pineal gland as the body's "aging clock." It appears to function as the body's timekeeper by ensuring it remains in sync with the most constant environmental cue available: the light-dark cycle.
The pineal gland's role is to signal to the rest of the body whether it's dawn or dusk, indicating whether it's time to be awake and alert or prepare for restorative sleep. This essential signal initiates a complex series of processes at the core of the balanced and harmonious state known as health. Prolonged disruption of the circadian rhythm (explained below) can lead to serious physical and psychological consequences.
Additionally, the pineal gland seems to act as the body's activities director for the human life cycle, functioning as a kind of "pacemaker." Scientists believe that the pineal gland, through its primary product, melatonin, initiates the onset of puberty and governs reproductive life. When the pineal gland ceases to release melatonin-directed signals, we age because our bodies can no longer operate efficiently and synchronously.