question: How and why does the hairs on your body stand during different conditions?
comment: The skin is not a perfectly smooth, continuous surface even though it may look like it. When you look very closely, you'll notice little dots called pores. Skin pores are linked to sweat glands under the skin, which are parts of your skin that produce sweat (which contains water) and release it onto your skin. Once on the skin, the sweat evaporates into the air, giving a cooling effect for your skin. Now water is also used in the body in reactions that generate heat, which are important in keeping you warm when it's cold outside. So you don't want to lose any water when you're cold. In parts of the body where hair grows, some of the pores have hair coming out of them. These hairs usually lie flat (on your arm for example) but stand up when it's cold. This closes off the skin pores, preventing water from being lost as sweat, meaning that you have more water to use to generate heat (and no water is used to keep you cool by sweating). Hairs also stand up when you're scared or get goosebumps. What these 3 have in common is that they all cause you to shiver, which causes blood vessels to become temporarily narrower to reduce the heat lost from blood. The way the hairs stand up is that they are attached to these small muscles next to the sweat glands, called "arrector pili" muscles. These will contract in response to shivering and cause the hairs to stand up.
passages: Section::::In cold conditions.
  
  BULLET::::- Heat is lost mainly through the hands and feet.
  
  BULLET::::- Sweat production is decreased.
  
  BULLET::::- The minute muscles under the surface of the skin called arrector pili muscles (attached to an individual hair follicle) contract (piloerection), lifting the hair follicle upright. This makes the hairs stand on end, which acts as an insulating layer, trapping heat. This is what also causes goose bumps since humans do not have very much hair and the contracted muscles can easily be seen.
   Section::::Mammals.
  
  Detection of hydrodynamic stimuli in mammals typically occurs through use of hairs (vibrissae) or “push-rod” mechanoreceptors, as in platypuses. When hairs are used, they are often in the form of whiskers and contain a follicle-sinus complex (F-SC), making them different from the hairs with which humans are most familiar.
  
  Section::::Mammals.:Pinnipeds.
   It can show postural changes where it changes its body shape or moves and exposes different areas to the sun/shade, and through radiation, convection and conduction, heat exchange occurs. Vasomotor responses allow control of the flow of blood between the periphery and the core to control heat loss from the surface of the body. Lastly, the organism can show insulation adjustments; a common example being “goosebumps” in humans where hair follicles are raised by pilomotor muscles, also shown in animals’ pelage and plumage.
  
  Section::::In humans.
   Secondly, hot roots can be the result of a single color process. If a darker shade of natural hair color is being lightened with a permanent hair color, the heat produced by the scalp can cause the hair nearest it to lighten more and/or become warmer than the ends of the hair.
   The sweat glands in humans could have evolved to spread from the hands and feet as the body hair changed, or the hair change could have occurred to facilitate sweating. Horses and humans are two of the few animals capable of sweating on most of their body, yet horses are larger and still have fully developed fur. In humans, the skin hairs lie flat in hot conditions, as the arrector pili muscles relax, preventing heat from being trapped by a layer of still air between the hairs, and increasing heat loss by convection.
   Research is currently being done to test detection of hydrodynamic stimuli in manatees. While the anatomy of the follicle-sinus complexes of manatees have been well studied, there is much to learn about the neural circuits involved if such detection is possible and the way in which the hairs encode information about strength and location of a stimulus via timing differences in firing.
  
  Section::::Mammals.:Platypuses.
   BULLET::::- The hair on the skin lie flat, preventing heat from being trapped by the layer of still air between the hair. This is caused by tiny muscles under the surface of the skin called arrector pili muscles relaxing so that their attached hair follicles are not erect. These flat hairs increase the flow of air next to the skin increasing heat loss by convection. When environmental temperature is above core body temperature, sweating is the only physiological way for humans to lose heat.
   BULLET::::1. In "Drosophila": A classic example of gene–environment interaction was performed on "Drosophila" by Gupta and Lewontin in 1981. In their experiment they demonstrated that the mean bristle number on "Drosophila" could vary with changing temperatures. As seen in the graph to the right, different genotypes reacted differently to the changing environment. Each line represents a given genotype, and the slope of the line reflects the changing phenotype (bristle number) with changing temperature. Some individuals had an increase in bristle number with increasing temperature while others had a sharp decrease in bristle number with increasing temperature. This showed that the norms of reaction were not parallel for these flies, proving that gene–environment interactions exist.
   One possible explanation for plant thermoregulation is to provide protection against cold temperature. For example, the skunk cabbage is not frost-resistant, yet it begins to grow and flower when there is still snow on the ground. Another theory is that thermogenicity helps attract pollinators, which is borne out by observations that heat production is accompanied by the arrival of beetles or flies.
  
  Section::::Behavioral temperature regulation.
   Section::::The elephant tail hair: how many things they can say!:Wet and dry seasons: different responses.
   Section::::Development.
  
  Hair follicles are to varying degrees sensitive to androgen, primarily testosterone and its derivatives, particularly dihydrotestosterone, with different areas on the body having different sensitivity. As androgen levels increase, the rate of hair growth and the weight of the hairs increase. Genetic factors determine both individual levels of androgen and the hair follicle's sensitivity to androgen, as well as other characteristics such as hair colour, type of hair and hair retention.
   Two forms of ADS regulation include environmental induction and biochemical regulatory switches. Under normal conditions, ADS is expressed at low levels in "Artemisia annua"; however, when exposed to cold, heat shock, or UV light, the ADS becomes upregulated. Corresponding with this in nature, cold-acclimated "Artemisia annua" express higher levels of ADS than plants under normal conditions.
   Section::::Location.
  
  In humans, temperature sensation enters the spinal cord along the axons of Lissauer's tract that synapse on second order neurons in grey matter of the dorsal horn, one or two vertebral levels up. The axons of these second order neurons then decussate, joining the spinothalamic tract as they ascend to neurons in the ventral posterolateral nucleus of the thalamus.
   In addition to other organisms, plants (Plantae) can be either stenothermic or eurythermic. Plants inhabiting the boreal and polar climates generally tend to be cold-eurythermic, enduring temperatures as cold as –85°, and as warm as at least 20 °C, such as boreal deciduous conifers. This is in direct contrast to plants that typically inhabit more tropical or montane regions, where plants may have purely tolerable range between only about 10° and 25 °C, such as the banyan tree.
  
  Section::::Eurythermal Protein Adaptation.
   Genetic processes work in combination with an organism's environment and experiences to influence development and behavior, often referred to as nature versus nurture. The intracellular or extracellular environment of a cell or organism may switch gene transcription on or off. A classic example is two seeds of genetically identical corn, one placed in a temperate climate and one in an arid climate. While the average height of the two corn stalks may be genetically determined to be equal, the one in the arid climate only grows to half the height of the one in the temperate climate due to lack of water and nutrients in its environment.
   Generally, the experimental measure of climate adaptation is conducted by exposing an experimental population to different environmental stimuli. Successful studies outside of a laboratory setting take place in locations with a variable annual climate. Areas where annual temperature and weather extremes vary greatly can give insight into the climate adaptability of organisms that live there. Tropical or arctic microclimates, for example, would be ideal settings for experimentation, as annual temperature and weather can vary greatly. Additionally, laboratory settings could work with certain creatures that have defense mechanisms for certain environmental changes, such as "Drosophila"'s chill-coma adaptation.
   Section::::Controls of variables.
  
  Section::::Controls of variables.:Core temperature.
  
  Mammals regulate their core temperature using input from thermoreceptors in the hypothalamus, brain, spinal cord, internal organs, and great veins. Apart from the internal regulation of temperature, a process called allostasis can come into play that adjusts behaviour to adapt to the challenge of very hot or cold extremes (and to other challenges). These adjustments may include seeking shade and reducing activity, or seeking warmer conditions and increasing activity, or huddling.
   PRR7 and PRR9 also play a role in the entrainment of "A. thaliana" to a temperature cycle. Double-mutant plants with inactivated "PRR7" and "PRR9" exhibit extreme period lengthening at high temperatures but show no change in period at low temperatures. However, the inactivation of "CCA1" and "LHY" in the "PRR7/PRR9" loss-of-function mutants shows no change in period at high temperatures—this suggests that "PRR7" and "PRR9" are acting by overcompensation.
  
  Section::::Interactions Within Arabidopsis.
   Section::::In plants.
  
  Thermogenesis occurs in the flowers of many plants in the Araceae family as well as in cycad cones. In addition, the sacred lotus ("Nelumbo nucifera") is able to thermoregulate itself, remaining on average 20 °C (36 °F) above air temperature while flowering. Heat is produced by breaking down the starch that was stored in their roots, which requires the consumption of oxygen at a rate approaching that of a flying hummingbird.
   The way in which new structures mature as they are produced may be affected by the point in the plants life when they begin to develop, as well as by the environment to which the structures are exposed. Temperature has a multiplicity of effects on plants depending on a variety of factors, including the size and condition of the plant and the temperature and duration of exposure. The smaller and more succulent the plant, the greater the susceptibility to damage or death from temperatures that are too high or too low. Temperature affects the rate of biochemical and physiological processes, rates generally (within limits) increasing with temperature.
   Section::::Causes.
   This variation of input signals calls for a variety of cells of the cortex in lamina 1 to have different modality-selectiveness and morphologies. These varying neurons are responsible for the different feelings we perceive in our body and can be classified by their responses to ranges of stimuli. The brain uses the integration of these signals to maintain homeostasis in the body whether it is temperature related or pain related.
  
  Section::::Function.:Vanilloid receptor.
   Thermoreceptors are sensory receptors, which respond to varying [temperature]s. While the mechanisms through which these receptors operate is unclear, recent discoveries have shown that mammals have at least two distinct types of thermoreceptors.
  
  The bulboid corpuscle, is a cutaneous receptor a "cold-sensitive" receptor, that detects cold temperatures. The other type is a warmth-sensitive receptor.
  
  Section::::Types and function.:External.:Mechanoreceptors.
  
  Mechanoreceptors are sensory receptors which respond to mechanical forces, such as pressure or distortion.
   Regional heterothermy describes organisms that are able to maintain different temperature "zones" in different regions of the body. This usually occurs in the limbs, and is made possible through the use of counter-current heat exchangers, such as the rete mirabile found in tuna and certain birds. These exchangers equalize the temperature between hot arterial blood going out to the extremities and cold venous blood coming back, thus reducing heat loss. Penguins and many arctic birds use these exchangers to keep their feet at roughly the same temperature as the surrounding ice. This keeps the birds from getting stuck on an ice sheet. Other animals, like the Leatherback Sea Turtle, use the heat exchangers to gather, and retain heat generated by their muscular flippers. There are even some insects which possess this mechanism (see insect thermoregulation), the best-known example being bumblebees, which exhibit counter-current heat exchange at the point of constriction between the mesosoma ("thorax") and metasoma ("abdomen"); heat is retained in the thorax and lost from the abdomen. Using a very similar mechanism, the internal temperature of a honeybee's thorax can exceed 45 °C while in flight.
   In a humid environment, moisture penetrates the hair shaft and is absorbed into the cortex, causing the proteins there to swell. Different kinds of proteins absorb moisture and swell differently, causing the hair shaft to twist and bend in an irregular pattern. To prevent this, Schueller recommends using conditioners and styling products that contain dimethicone, which repels humidity. 
  