It is certain that the pineal gland takes over important tasks for the control of the circadian rhythm, the day-night rhythm. Certain structures connect the epithalamus with the olfactory centers and the visual pathway. Certain reflexes such as the pupil reflex, salivary reflex and others are most likely controlled by the epithalamus.
What is the epithalamus?
The epithalamus is part of the diencephalon and is located between the thalamus and the third cerebral ventricle. It is a small structure that includes the epiphysis (pineal gland), several connecting lanes (commissures), the reins (habenulae) and the praetectum (area pretectalis), which receives information from the retina via nerve fibers and controls the pupillary reflex.
The reins make the connection to the olfactory brain and the brain stem and receive from there information for controlling the salivary reflex. The smell of well fragrant food causes the salivation is stimulated and other physiological preparations of the digestive tract for food intake done. The epiphysis, which can also be counted among the endocrine glands, is the part of the epithalamus that controls the circadian rhythm, the day-night rhythm, through the synthesis of the control hormone melatonin.
Through a very complex system of signal transduction and signal processing, the epiphysis receives light stimuli and other information from the retina of the eyes, which feed into the control of the circadian rhythm.
Anatomy & Construction
The epithalamus includes the following structures as part of the diencephalon: the epiphysis, also called the pineal gland, the habenula (rein), the subcommissural organ, the posterior commissure, and the neural core areas of the habenulae and the pretectal area. The habenulae do not consist of nerve fiber strands, but of an accumulation of neuronal nuclei, which means that it is not just about incoming or outgoing nerve signals, but also the processing of the signals, that is, unconscious decisions for particular circuits and reflexes.
The core accumulations in the reins are very likely to form the interconnections between the brain stem and the olfactory bulb, so that a complex food preparation cascade can be started when "nourishing" odors arrive. The epiphysis contains a large amount of hormone-producing pinealocytes, which are honeycomb-like segmented by connective tissue cells. Glial cells are present to support the tissue. For the functional control of hormone production in the context of the circadian control of many bodily functions, the epiphysis has correspondingly many nerve fibers.
Function & Tasks
Although some subtasks and functions of the epithalamus are known, especially those of the epiphysis, there is still a broad field of research that would allow further insights into the function and functions of the epithalamus and its structures. It seems certain that the epithalamus in one of its tasks acts as a switch between the olfactory center (olfactory brain) in the brain stem and the epiphysis, with the epiphysis being regarded by most authors as part of the epithalamus.
This special function is not just about the salivary reflex, which causes the production of pleasant smells to stimulate the production of saliva, but also involves more complex preparations of the body for the intake of certain foods. Part of the physiological preparation of the body is, among other things, a targeted stimulation of acid production and also of insulin synthesis if the ingested food fragrance can be expected to produce easily digestible carbohydrates.
The epiphysis plays an important role in the circadian rhythm and is based on the one hand on body-internal clocks and the day-night change. At night - assuming darkness - the epiphysis produces hormones that convert the messenger serotonin into melatonin. Melatonin plays an important role in many physiological processes that are supposed to set the body to sleep. Blood pressure and heart rate decrease, the ability to concentrate decreases and drowsiness occurs. The concentration of stress hormones also decreases, and a number of other physiological processes occur unconsciously in the body.
Shift work or frequent changes of time zones can disturb this regulatory mechanism so much that it leads to physical symptoms in the long term. In long-haul flights, it has been customary for some years to bring the lighting in the cockpit to a certain brightness value (lux) in the dark in order to suppress melatonin production. People who spend short periods of time in other time zones may try to keep the rhythm of the time zone they normally spend in as much as possible. This supports a smooth return to the traditional time zone and reduces the jet lag symptoms.
Diseases and symptoms directly related to epithalamus are very rare. The most common problems are caused by indirect disturbances of the epithalamus when mechanical pressure on structures of the epithalamus and the epiphysis is exerted by tumors or hemorrhages in the brain.
If the cause of the impairment can be overcome, the symptoms usually disappear by themselves. In the rare cases where the epiphysis is directly affected, pineal cysts are the most common form of the disease. These are benign cysts that form in the epiphysis. The disease is often accompanied by symptoms such as headache and nausea. It can also lead to visual or balance disorders. If the cysts reach a certain size, it can come to untreated by a damming of the brain water to the formation of a water head (hydrocephalus).
A very rare epiphyseal tumor originating from melatonin-producing cells is pinealoblastoma. A more common epiphyseal tumor is a germ cell tumor, which is usually benign (benign tumor) in women, but predominantly malignant (malignant tumor) in men.