question: Why does the burn of putting your leg in hot water seem to come a second or so after it’s been pulled out?
comment: So there’s ‘two’ nervous systems that usually work together. This is an example of where one takes over first. - CNS = Brain. It controls the actions you think about so it takes longer to work. - PNS = No Brain. Controls reflex actions, ones you don’t have to think about, so it’s faster. The leg in hot water reaction would work something like this: 1. Leg goes into water 2. PNS realises you are in danger. 3. PNS moves leg out of the water because it knows you’re in danger. 4. CNS realises leg is out of water 5. CNS realises leg is in pain and lets the brain know, meaning you only then feel pain. I hope that’s simple enough, ask any questions if you need clarification.
passages: First, nociception is required. This is the ability to detect noxious stimuli which evoke a reflex response that rapidly moves the entire animal, or the affected part of its body, away from the source of the stimulus. The concept of nociception does not imply any adverse, subjective "feeling" – it is a reflex action. An example would be the rapid withdrawal of a finger that has touched something hot – the withdrawal occurs before any sensation of pain is actually experienced.
   As with any surgical procedure, cardiac catheterizations come with a generic list of possible complications. One of the complications that are sometimes reported involves some temporary nerve involvement. Sometimes a small amount of swelling occurs that can put pressure on nerves in the area of the incision. Venous thrombosis is the most common complication with an incidence ranging between 0.5 and 2.5%. There have been reports of patients feeling like they have hot fluid like blood or urine running down their leg for up to a month or two after the incision has healed. This usually passes with time, but patients should tell their doctor if they have these symptoms and if they last.
   BULLET::::- Multiple bee-sting like pains in the affected area
  
  BULLET::::- Occasionally, aching in the groin area or pain spreading across the buttocks
  
  BULLET::::- Usually more sensitive to light touch than to firm pressure
  
  BULLET::::- Hyper sensitivity to heat (warm water from shower feels like it is burning the area)
  
  BULLET::::- Occasionally, patients may complain of itching or a bothersome sensation rather than pain in the affected area.
  
  The entire distribution of the nerve is rarely affected. Usually, the unpleasant sensation(s) affect only part of the skin supplied by the nerve.
  
  Section::::Cause.
   Arthus reaction
  
  In immunology, the Arthus reaction () is a type of local type III hypersensitivity reaction. Type III hypersensitivity reactions are immune complex-mediated, and involve the deposition of antigen/antibody complexes mainly in the vascular walls, serosa (pleura, pericardium, synovium), and glomeruli. This reaction is usually encountered in experimental settings following the injection of antigens.
  
  Section::::History.
  
  The Arthus reaction was discovered by Nicolas Maurice Arthus in 1903. Arthus repeatedly injected horse serum subcutaneously into rabbits. After four injections, he found that there was edema and that the serum was absorbed slowly. Further injections eventually led to gangrene.
  
  Section::::Process.
   When thin and flexible instruments are used the immediate experience of pain is described as acutely stinging and searing. The instant sensations are disproportionally intense compared to the applied force and reflexively radiate through the body. The subsequent pain sensations of a succession of strokes are often described as throbbing, piercing or burning and gradually ease off within a few hours. A slightly stinging or nagging sensation often remains perceptible for a couple of days, especially while walking.
   Acetic acid (a strong irritant) applied to the hindlimb of frogs elicits vigorous wiping of the exposed skin; both pH and osmolarity may contribute to the nociception produced. This response is used in a standard test for analgesic effects in frogs, commonly termed the "acetic acid test". In this procedure, dilutions of the acid are placed drop-wise on the dorsum of the frog's thigh until the frog wipes the affected area.
   Uhthoff's phenomenon
  
  Uhthoff's phenomenon (also known as Uhthoff's syndrome, Uhthoff's sign, and Uhthoff's symptom) is the worsening of neurologic symptoms in multiple sclerosis (MS) and other neurological, demyelinating conditions when the body gets overheated from hot weather, exercise, fever, or saunas and hot tubs. It is possibly due to the effect of increased temperature on nerve conduction. With an increased body temperature, nerve impulses are either blocked or slowed down in a damaged nerve but once the body temperature is normalized, signs and symptoms may disappear or improve.
  
  Section::::Clinical significance.
   The nerve may become painful over a period of time as weight gain makes underwear, belting or the waistband of pants gradually exert higher levels of pressure. Pain may be acute and radiate into the rib cage, and into the groin, thigh, and knee. Alternately, weight loss or aging may remove protective fat layers under the skin, so the nerve can compress against underwear, outer clothing, and—most commonly— by belting. Long periods of standing or leg exercise that increases tension on the inguinal ligament may also cause pressure.
   After studying for his Ph.D. in 1954 with D. O. Hebb at McGill University in Montreal, he began to work with patients who suffered from "phantom limb" pain — people who feel pain in an arm or leg that has been removed. He found that pain often has little survival value, and some pains are entirely out of proportion to the degree of tissue damage, sometimes continuing long after injured tissues have healed. While still a postdoctoral student, Melzack began collecting "pain words" and putting them into classes that belonged together, like "hot," "burning," "scalding," and "searing".
   "The treatise of nervous sections" is a 548-page book which mentions 226 references in five languages: Latin, French, English, Italian, and German. Létiévant had not only read Galen and Ambroise Paré, but Paul Broca, Charles-Édouard Brown-Séquard, and even Silas Weir Mitchell. Two of the main topics of this treatise are: 1. Aesthesiography (from the Greek: aisthêsis) a new concept proposed by Létiévant, is a map of the incomplete anaesthesia which "facilitates the interpretation" of the cutaneous nerve lesions. Létiévant presents nine illustrations drawn by himself. 2. Tingling sign. Létiévant had already observed that pressure over the median nerve at the site of the repair or at a point distal to the repair, caused painful tingling in the fingers. It was then, in 1915, correctly interpreted as Tinel's sign.
   Axon reflex suggests that the afferent fiber is bifurcated before connecting to the dorsal horn. Bifurcated fibers do exist in muscle, skin, and intervertebral discs. Yet these particular neurons are rare and are not representative of the whole body. Axon-Reflex also does not explain the time delay before the appearance of referred pain, threshold differences for stimulating local and referred pain, and somatosensory sensibility changes in the area of referred pain.
  
  Section::::Mechanism.:Hyperexcitability.
   BULLET::::- Psoas sign, also known as "Obraztsova's sign", is right lower-quadrant pain that is produced with either the passive extension of the right hip or by the active flexion of the person's right hip while supine. The pain that is elicited is due to inflammation of the peritoneum overlying the iliopsoas muscles and inflammation of the psoas muscles themselves. Straightening out the leg causes pain because it stretches these muscles, while flexing the hip activates the iliopsoas and causes pain.
   As assessments of whether the right to an expeditious trial has been granted must be made on an ad hoc basis, McGuinness J concluded that taken as a whole, "the delays in the latter period of the prosecution of the applicant amount to a denial of his right to an expeditious trial. There is also a real risk that this may lead to an unfair trial.”
   Newts flick their tails in response to it being irradiated by a hot beam, in a very similar manner to that observed in rodents being used in the tail flick test.
  
  The threshold to Von Frey hairs and response to nociceptive withdrawal can be used to measure the effectiveness of analgesia.
  
  Section::::Research findings.:Avoidance learning.
   The two basic types of sensation are touch-position and pain-temperature. Touch-position input comes to attention immediately, but pain-temperature input reaches the level of consciousness after a delay; when a person steps on a pin, the awareness of stepping on something is immediate but the pain associated with it is delayed.
   In the nervous system there is a "closed loop" system of sensation, decision, and reactions. This process is carried out through the activity of sensory neurons, interneurons, and motor neurons. A touch or painful stimulus, for example, creates a sensation in the brain only after information about the stimulus travels there via afferent nerve pathways.
  
  Section::::Etymology and mnemonics.
  
  Afferent is derived from Latin participle "afferentem" ("af- = ad-" : to + "ferre" : bear, carry), meaning carrying into.
   Many illusions in vision are caused by adaptation, the prolonged exposure to a previous stimulus. In such cases, the perception of a subsequent stimulus is altered. This phenomenon is sometimes referred to as a contingent after-effect. Similarly, adaptation can cause such illusions in the sense of touch.
  
  BULLET::::- If one hand is immersed in cold water and the other in hot for a minute or so, and then both hands are placed in lukewarm water, the lukewarm water will feel hot to the hand previously immersed in cold water, and cold to the hand previously immersed in hot water.
   The beginning of Galvani's experiments with bioelectricity has a popular legend which says that the Galvani was slowly skinning a frog at a table where he and his wife had been conducting experiments with static electricity by rubbing frog skin. Galvani's assistant touched an exposed sciatic nerve of the frog with a metal scalpel that had picked up a charge. At that moment, they saw sparks and the dead frog's leg kicked as if in life. The observation made the Galvanis the first investigators to appreciate the relationship between electricity and animation—or life. This finding provided the basis for the new understanding that the impetus behind muscle movement was electrical energy carried by a liquid (ions), and not air or fluid as in earlier balloonist theories.
   Scalds can be more severe when steam impinges on the naked skin, because steam can reach higher temperatures than water and transfers latent heat by condensation. On the other hand when clothes are soaked with hot water the heat transfer is often of a longer duration since the body part can not be removed from the heat source as quickly. 
   BULLET::::- PMF 5088 (1948) - "Peroneal Nerve Anastomosis at the Knee"; Case of peroneal nerve severed at bend of knee with evident foot drop and loss of sensation on dorsum of foot; technique used to effect repair; necessity for gently curving incision to prevent later keloid formation or contracture by avoiding flexion creases in popliteal space (7 min; color).
  
  BULLET::::- PMF 5089 -
  
  BULLET::::- PMF 5095 -
   Perrin (France) is reported to have first recorded this condition in 1845. The periodic nature of infusions was noted by CH Moore (Middlesex Hospital, UK) in 1852.
   The hunting reaction is one out of four possible responses to immersion of the finger in cold water. The other responses observed in the fingers after immersion in cold water are a continuous state of vasoconstriction, slow steady and continuous rewarming and a proportional control form in which the blood vessel diameter remains constant after an initial phase of vasoconstriction. However, the vast majority of the vascular responses to immersion of the finger in cold water can be classified as the hunting reaction.
   BULLET::::- Pain while operating automobiles
  
  BULLET::::- Pain along the Posterior Tibial nerve path
  
  BULLET::::- Burning sensation on the bottom of foot that radiates upward reaching the knee
  
  BULLET::::- "Pins and needles"-type feeling and increased sensation on the feet
  
  BULLET::::- A positive Tinel's sign
  
  Tinel's sign is a tingling electric shock sensation that occurs when you tap over an affected nerve. The sensation usually travels into the foot but can also travel up the inner leg as well.
  
  Section::::Causes.
   Descartes advanced a theory on automatic bodily reactions to external events which influenced 19th-century reflex theory. He argued that external motions such as touch and sound reach the endings of the nerves and affect the animal spirits. Heat from fire affects a spot on the skin and sets in motion a chain of reactions, with the animal spirits reaching the brain through the central nervous system, and in turn animal spirits are sent back to the muscles to move the hand away from the fire. Through this chain of reactions the automatic reactions of the body do not require a thought process.
   Recently this idea has regained some credibility under a new term, central sensitization. Central sensitization occurs when neurons in the spinal cord's dorsal horn or brainstem become more responsive after repeated stimulation by peripheral neurons, so that weaker signals can trigger them. The delay in appearance of referred pain shown in laboratory experiments can be explained due to the time required to create the central sensitization.
  
  Section::::Mechanism.:Axon-reflex.
  