Name | Pineal gland |
---|---|
Latin | glandula pinealis |
Graysubject | 276 |
Graypage | 1277 |
Image2 | Illu_pituitary_pineal_glands.jpg |
Caption2 | Diagram of pituitary and pineal glands in the human brain |
Precursor | Neural Ectoderm, Roof of Diencephalon |
Artery | superior cerebellar artery |
Meshname | Pineal+gland |
Neurolex | Pineal body |
Neurolexid | birnlex_1184 |
Dorlandspre | g_06 |
Dorlandssuf | 12392585}} |
The pineal gland is a midline structure, and is often seen in plain skull X-rays, as it is often calcified.
The pineal gland consists mainly of pinealocytes, but four other cell types have been identified. As it is quite cellular (in relation to the cortex and white matter) it may be mistaken for a neoplasm.
The pineal gland receives a sympathetic innervation from the superior cervical ganglion. However, a parasympathetic innervation from the sphenopalatine and otic ganglia is also present. Further, some nerve fibers penetrate into the pineal gland via the pineal stalk (central innervation). Finally, neurons in the trigeminal ganglion innervate the gland with nerve fibers containing the neuropeptide, PACAP. Human follicles contain a variable quantity of gritty material, called corpora arenacea (or "acervuli," or "brain sand"). Chemical analysis shows that they are composed of calcium phosphate, calcium carbonate, magnesium phosphate, and ammonium phosphate. In 2002, deposits of the calcite form of calcium carbonate were described. Calcium, phosphorus and fluoride
In some vertebrates, exposure to light can set off a chain reaction of enzymatic events within the pineal gland that regulate circadian rhythms. Some early vertebrate fossil skulls have a pineal foramen (opening). This correlates with the physiology of the modern "living fossils," the lamprey and the tuatara, and some other vertebrates that have a parietal organ or "third eye," which, in some of them, is photosensitive. The third eye represents evolution's earlier approach to photoreception. The structures of the third eye in the tuatara are homologous to the cornea, lens and retina, though the latter resembles that of an octopus rather than a vertebrate retina. The asymmetrical whole consists of the "eye" to the left and the pineal sac to the right. "In animals that have lost the parietal eye, including mammals, the pineal sac is retained and condensed into the form of the pineal gland." it has profuse blood flow, second only to the kidney.
Fossils seldom preserve soft anatomy. The brain of the Russian Melovatka bird, about 90 million years old, is an exception, and it shows a larger-than-expected parietal eye and pineal gland.
In humans and other mammals, the light signals necessary to set circadian rhythms are sent from the eye through the retinohypothalamic system to the suprachiasmatic nuclei (SCN) and the pineal.
Melatonin is N-acetyl-5-methoxy-tryptamine, a derivative of the amino acid tryptophan, which also has other functions in the central nervous system. The production of melatonin by the pineal gland is stimulated by darkness and inhibited by light. Photosensitive cells in the retina detect light and directly signal the SCN, entraining its rhythm to the 24-hour cycle in nature. Fibers project from the SCN to the paraventricular nuclei (PVN), which relay the circadian signals to the spinal cord and out via the sympathetic system to superior cervical ganglia (SCG), and from there into the pineal gland. The function(s) of melatonin in humans is not clear; it is commonly prescribed for the treatment of circadian rhythm sleep disorders.
The compound pinoline is also produced in the pineal gland; it is one of the beta-carbolines.
The human pineal gland grows in size until about 1–2 years of age, remaining stable thereafter, although its weight increases gradually from puberty onwards. The abundant melatonin levels in children are believed to inhibit sexual development, and pineal tumors have been linked with precocious puberty. When puberty arrives, melatonin production is reduced. Calcification of the pineal gland is typical in adults.
In animals, the pineal gland appears to play a major role in sexual development, hibernation, metabolism, and seasonal breeding.
Pineal cytostructure seems to have evolutionary similarities to the retinal cells of chordates.
Studies on rodents suggest that the pineal gland may influence the actions of recreational drugs, such as cocaine, and antidepressants, such as fluoxetine (Prozac), and its hormone melatonin can protect against neurodegeneration.
René Descartes, who dedicated much time to the study of the pineal gland, called it the "seat of the soul." He believed that it was the point of connection between the intellect and the body. The relevant quotation as to Descartes' reason for believing this is,
Baruch de Spinoza later refuted:
The notion of a "pineal-eye" is central to the philosophy of the French writer Georges Bataille, which is analyzed at length by literary scholar Denis Hollier in his study Against Architecture. In this work Hollier discusses how Bataille uses the concept of a "pineal-eye" as a reference to a blind-spot in Western rationality, and an organ of excess and delirium. This conceptual device is explicit in his surrealist texts, The Jesuve and The Pineal Eye.
Category:Glands Category:Endocrine system Category:Head and neck Category:Sleep physiology Category:Circadian rhythms
This text is licensed under the Creative Commons CC-BY-SA License. This text was originally published on Wikipedia and was developed by the Wikipedia community.
Category:Living people Category:American filmmakers Category:1973 births Category:People of Upstate New York Category:Conspiracy theorists Category:UFO conspiracy theorists
This text is licensed under the Creative Commons CC-BY-SA License. This text was originally published on Wikipedia and was developed by the Wikipedia community.
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