User:Vhensey/sandbox

Note to Peer Reviewers
I am having trouble determining whether my writing in this draft is too technical for Wikipedia. Any comments on this would be appreciated. In linking articles to words that are field-specific, is this sufficient? Is there anything else I can do to make the language here accessible to the general population? Another issue I have been coming across is the overlap between the information I think should be in this article and what I have seen in related articles. Comments on that would be appreciated as well.

Denoted in double parenthesis are my comments about different sections (since square brackets indicate links in Wikipedia). The comments are organizational or asking for peer suggestions. I am aware that this draft is pieced awkwardly and not filled out as completely as I would like. In adding what is in this Sandbox to the existing article, I hope to smoothly integrate the information and continue to fill out sections that seem incomplete. I am more concerned about language and content right now, rather than flow of the writing, although comments regarding the flow of the finished project are appreciated.

((add to)) Introduction
Melatonin plays a large role in effects of light on circadian rhythms. When an organism is exposed to a light stimulus, the hormone melatonin is suppressed, or prevented from being secreted by the pineal gland.

The reason why entrainment occurs in humans is because each individual's circadian rhythm is longer than 24 hours (majority of population) or shorter than 24 hours (minority of population).

((add to)) Demonstrated Effects
((In the existing article, this section covers all that I would typically cover. Should I expand upon what's already there?))

Internal Pathways and Mechanisms ((add this between Demonstrated Effects and Internal Regulators))
Light first passes into a mammal's system through the retina, then takes one of two paths: the light either gets collected by rod cells and cone cells before being transmitted to the retinal ganglion cells (RGCs), or it is directly collected by these RGCs. The RGCs use the photopigment melanopsin to absorb the light energy. Specifically, this class of RGCs being discussed is referred to as "intrinsically photosensitive," which just means they are sensitive and respond to light. There are five known types of intrinsically photosensitive retinal ganglion cells (ipRGCs): M1, M2, M3, M4, and M5. These connect to amacrine cells in the inner plexiform layer of the retina. Ultimately, via this retinohypothalamic tract (RHT) the suprachiasmatic nucleus (SCN) of the hypothalamus receives light information from these ipRCGs.

The core region of the SCN houses the majority of light-sensitive neurons. From here, signals must reach the rest of the SCN in order for circadian shifts, or entrainment, to occur.

Some important structures directly impacted by the light-sleep relationship are the superior colliculus-pretectal area and the ventrolateral preoptic nucleus.

((add to)) Internal Regulators
((I plan on cleaning up this section in the existing article. It seems way too technical and detailed in explaining the studies cited. How do I change the language to fit Wikipedia?))

Genes are what determine the regulation of circadian rhythm in conjunction with light. When light activates NMDA receptors in the SCN, CLOCK gene expression in that region is altered and the SCN is reset, and this is how entrainment occurs. Specific genes involved with entrainment are PER1 and PER2.

Downstream Effects ((add section))
While light has direct effects on circadian rhythm, there are indirect effects seen across studies. Seasonal affective disorder creates a model in which decreased day length during autumn and winter increases depressive symptoms. A shift in the circadian phase response curve creates a connection between the amount of light in a day (day length) and depressive symptoms in this disorder. Light seems to have therapeutic antidepressant effects when an organism is exposed to it at appropriate times during the circadian rhythm, regulating the sleep-wake cycle.

In addition to mood, learning and memory become impaired when the circadian system shifts due to light stimuli, which can be seen in studies modeling jet lag and shift work situations. Frontal and parietal lobe areas involved in working memory have been implicated in melanopsin responses to light information.

In response to light exposure, alertness levels can increase as a result of suppression of melatonin secretion. A linear relationship has been found between alerting effects of light and activation in the posterior hypothalamus.

Disruption of circadian rhythm as a result of light also produces changes in metabolism.