question: I've read somewhere that digestion actually is very painful but our brain ignores it. as well as that we constantly hear our insides activity, but our brain again ignores it. is that true and how does that work?
comment: Digestion isn’t painful, because pain is different than what a lot of people may realize. It’s just stimulation of pain nerves, which are generally activated by stimulus capable of causing physical damage as well. The muscle contractions used in digestion are the same we use to swallow and do many other things, and your stomach is layered with mucus and tissues to protect it from acid. Unless you have a medical condition, there should be no pain.
passages: Section::::Systematic response.:Digestive-system response.
  
  Section::::Systematic response.:Digestive-system response.:Cephalic phase.
   Long reflexes to the digestive system involve a sensory neuron sending information to the brain, which integrates the signal and then sends messages to the digestive system. While in some situations, the sensory information comes from the GI tract itself; in others, information is received from sources other than the GI tract. When the latter situation occurs, these reflexes are called feedforward reflexes. This type of reflex includes reactions to food or danger triggering effects in the GI tract. Emotional responses can also trigger GI response such as the butterflies in the stomach feeling when nervous. The feedforward and emotional reflexes of the GI tract are considered cephalic reflexes.
   Section::::Systematic response.:Digestive-system response.:Enteric nervous system.
  
  The digestive system is also able to respond to internal stimuli. The digestive tract, or enteric nervous system alone contains millions of neurons. These neurons act as sensory receptors that can detect changes, such as food entering the small intestine, in the digestive tract. Depending on what these sensory receptors detect, certain enzymes and digestive juices from the pancreas and liver can be secreted to aid in metabolism and breakdown of food.
  
  Section::::Research methods and techniques.
  
  Section::::Research methods and techniques.:Clamping techniques.
   Section::::Regulation.:Short reflexes.
   Section::::Myths about the causes of post-prandial somnolence.
  
  Section::::Myths about the causes of post-prandial somnolence.:Cerebral blood flow and oxygen delivery.
  
  Although the passage of food into the gastrointestinal tract results in increased blood flow to the stomach and intestines, this is achieved by diversion of blood primarily from skeletal muscle tissue and by increasing the volume of blood pumped forward by the heart each minute. The flow of oxygen and blood to the brain is extremely tightly regulated by the circulatory system and does not drop after a meal.
  
  Section::::Myths about the causes of post-prandial somnolence.:Turkey and tryptophan.
   General visceral afferent sensations are mostly unconscious visceral motor reflex sensations from hollow organs and glands that are transmitted to the CNS. While the unconscious reflex arcs normally are undetectable, in certain instances they may send pain sensations to the CNS masked as referred pain. If the peritoneal cavity becomes inflamed or if the bowel is suddenly distended, the body will interpret the afferent pain stimulus as somatic in origin. This pain is usually non-localized. The pain is also usually referred to dermatomes that are at the same spinal nerve level as the visceral afferent synapse.
  
  Section::::Function.:Vascular effects.
   It is in most animals a normal and voluntary process unlike the complex vomiting reflex in response to toxins. Honey is produced by a process of regurgitation by honey bees, which is stored in the beehive as a primary food source.
  
  Section::::Humans.
  
  In humans it can be voluntary or involuntary, the latter being due to a small number of disorders. Regurgitation of a person's meals following ingestion is known as rumination syndrome, an uncommon and often misdiagnosed motility disorder that affects eating. It may be a symptom of gastroesophageal reflux disease (GERD).
   Some areas of the brain that are correlated with the subjective experience of pain were activated in MCS patients when noxious stimulation was present. Positron emission tomography (PET) scans found increased blood flow to the secondary sensory cortex, posterior parietal cortex, premotor cortex, and the superior temporal cortex. The pattern of activation, however, was with less spatial extent. Some parts of the brain were less activated than normal patients during noxious stimulus processing. These were the posterior cingulate, medial prefrontal cortex, and the occipital cortex. Even though functional brain imaging can objectively measure changes in brain function during noxious stimulation, the role of different areas of the brain in pain processing is only partially understood. Furthermore, there is still the problem of the subjective experience. MCS patients by definition cannot consistently and reliably communicate their experiences. Even if they were able to answer the question "are you in pain?", there would not be a reliable response. Further clinical trials are needed to access the appropriateness of the use of analgesia in patients with MCS.
   Section::::Initiating ingestion.:Metabolic signals.
  
  Hunger is the result of a fall in blood glucose level or depriving cells of the ability to metabolize fatty acids—glucoprivation and lipoprivation, respectively, stimulate eating. Detectors in the brain are only sensitive to glucoprivation; detectors in the liver are sensitive to both glucoprivation and lipoprivation outside the blood–brain barrier. However, no single set of receptors is solely responsible for the information the brain uses to control eating.
  
  Section::::Satiety signals.
   While some only experience symptoms following some meals, most experience episodes following any ingestion, from a single bite to a large meal. However, some long-term patients will find a select couple of food or drink items that do not trigger a response.
  
  Unlike typical vomiting, the regurgitation is typically described as effortless and unforced. There is seldom nausea preceding the expulsion, and the undigested food lacks the bitter taste and odour of stomach acid and bile.
   During sham feeding sessions of both appetizing and unappetizing foods, 3 cycles per minute (cpm) power was measured. During the sham feeding of appetizing foods, 3cpm power increased. This increase was not reported in the sham feeding of unappetizing foods. The researchers concluded that the presence of this pattern seems to mark the beginning of the body preparing for digestion, and the absence of this pattern in the disgust condition could indicate that the body is readying to reject the food. The increase of 3cpm power is also linked with increased saliva and digestive juice production, all of which support the idea that this reflex, called the cephalic-vagal reflex, is the precursor of digestion. The differential response to appetizing and unappetizing foods suggest that the body uses disgust as a cue to whether a food is good to eat and responds accordingly.
   BULLET::::3. The viscera are relatively insensitive structures.
  
  BULLET::::- Cannon wrote that there is a common belief that the more deeply the body is penetrated, the more sensitive it becomes; however, this is not the case. In the nerves distributed to the viscera the afferent sensory fibers may be only 1/10th as numerous as the efferent sensory fibers. For example, in the case of the viscera, we are unaware of the contractions and relaxations of the digestive processes. Such processes are undemonstrative and beyond our physical awareness, even when marked changes are induced in them.
   BULLET::::- In "central sensitization," nociceptive neurons in the dorsal horns of the spinal cord become sensitized by peripheral tissue damage or inflammation. This type of sensitization has been suggested as a possible causal mechanism for chronic pain conditions. The changes of central sensitization occur after repeated trials to pain. Research from animals has consistently shown that when a trial is repeatedly exposed to a painful stimulus, the animal’s pain threshold will change and result in a stronger pain response. Researchers believe that there are parallels that can be drawn between these animal trials and persistent pain in people. For example, after a back surgery that removed a herniated disc from causing a pinched nerve, the patient may still continue to “feel” pain. Also, newborns who are circumcised without anesthesia have shown tendencies to react more greatly to future injections, vaccinations, and other similar procedures. The responses of these children are an increase in crying and a greater hemodynamic response (tachycardia and tachypnea).
   Computer-driven barostats have widely been used to assess sensation and pain thresholds in the gut. Assessment of pain thresholds in the ampulla recti has been proposed as diagnostic measure in irritable bowel syndrome.
   Studies suggest that patients acutely suffering from bulimia nervosa (BN) exhibit heightened interoceptive accuracy, but that some patients who have recovered from the disorder show reduced interoceptive awareness under resting physiological conditions. Further, BN patients consistently report reduced sensitivity to many other kinds of internal and external sensations, exhibiting increased thresholds to heat pain compared to healthy subjects and an increased gastric capacity. Neuroimaging literature suggests a pattern of heightened interoceptive awareness in patients with BN based on increased activity and volume in the insula and anterior cingulate cortex—regions associated with interoception and taste processing—when looking at food.
   Section::::Motility.:Contraction patterns.
  
  The patterns of GI contraction as a whole can be divided into two distinct patterns, peristalsis and segmentation. Occurring between meals, the migrating motor complex is a series of peristaltic wave cycles in distinct phases starting with relaxation, followed by an increasing level of activity to a peak level of peristaltic activity lasting for 5–15 minutes.
  
  This cycle repeats every 1.5–2 hours but is interrupted by food ingestion. The role of this process is likely to clean excess bacteria and food from the digestive system.
  
  Section::::Motility.:Contraction patterns.:Peristalsis.
   Fiber might be beneficial in those who have a predominance of constipation. In people who have IBS-C, soluble fiber can reduce overall symptoms, but will not reduce pain. The research supporting dietary fiber contains conflicting small studies complicated by the heterogeneity of types of fiber and doses used.
  
  One meta-analysis found only soluble fiber improved global symptoms of irritable bowel, but neither type of fiber reduced pain. 
   It was coined the "what-the-hell" effect by dieting researcher Janet Polivy in 2010. She describes this effect as the type of thinking which says, "What the hell, my diet’s already broken, so I might as well eat everything in sight." It has been observed that reducing the guilt of overeating through self-forgiveness can mitigate counterregulatory eating.
   If we accept pains as special qualia known absolutely but exclusively by the solitary minds that perceive them, this may be taken to ground a Cartesian view of the self and consciousness. Our consciousness, of pains anyway, would seem unassailable. Against this, one might acknowledge the absolute fact of one's own pain, but claim skepticism about the existence of anyone else's pains. Alternatively, one might take a behaviorist line and claim that our pains are merely neurological stimulations accompanied by a disposition to behave.
   Defecation involves conscious and subconscious processes, when the extrinsic nervous system is damaged either of these can be affected. Conscious processes are controlled by the somatic nervous system, these are voluntary movements for example the contraction of the striated muscle of the external anal sphincter is instructed to do so by the brain, which sends signals along the nerves innervating this muscle. Subconscious processes are controlled by the autonomic nervous system; these are involuntary movements such as contraction of the smooth muscle of the internal anal sphincter or the colon. The autonomic nervous system also provides sensory information; this could be about the level of distension within the colon or rectum.
   Section::::Human gastrointestinal tract.:Function.
  
  The time taken for food or other ingested objects to transit through the gastrointestinal tract varies depending on many factors, but roughly, it takes less than an hour after a meal for 50% of stomach contents to empty into the intestines while total emptying takes around 2 hours. Subsequently, 50% emptying of the small intestine takes between 1 and 2 hours. Finally, transit through the colon takes 12 to 50 hours with wide variation between individuals.
  
  Section::::Human gastrointestinal tract.:Function.:Immune function.
  
  Section::::Human gastrointestinal tract.:Function.:Immune function.:Immune barrier.
   On the other hand, there is also a report that casts a negative light on this theory. An online reporter conducted an experiment in which, in order to verify the effectiveness of bookstores in alleviating constipation, four constipated females were sent to a "trendy book cafe" to eat and drink. In order to prevent against the effects of false belief, the subjects were not told about the actual nature of the experiment (a blinded experiment). The result of the experiment was that, except for one subject with severe constipation, three of the test subjects soon achieved bowel movements.
   Chronic pain is another example that can originate from the drastic misinterpretation of pain as a catastrophe. As a result of this misinterpretation, the individual repeatedly avoids the pain-inducing activity and will likely overestimate any future pain from such activity. The excessive sensitivity to pain discourages the individual from exercise and weakens his or her body.
  
  Section::::Criticisms.
   The human gastrointestinal tract is around 9 meters long. Food digestion physiology varies between individuals and upon other factors such as the characteristics of the food and size of the meal, and the process of digestion normally takes between 24 and 72 hours.
   The vagovagal reflex is active during the receptive relaxation of the stomach in response to swallowing of food (prior to it reaching the stomach). When food enters the stomach a "vagovagal" reflex goes from the stomach to the brain, and then back again to the stomach causing active relaxation of the smooth muscle in the stomach wall. If vagal innervation is interrupted then intra-gastric pressure increases. This is a potential cause of vomiting due to the inability of the proximal stomach smooth muscle to undergo receptive relaxation.
  
presuppositions: Digestion is painful but the brain ignores it. Pain indicates harm.
corrections: Digestion should not be painful unless you have a medical condition. Pain is just the stimulation of pain nerves and doesn't necessarily indicate harm.
raw_presuppositions: Digestion is painful but the brain ignores it. Pain indicates harm.
raw_corrections: Digestion should not be painful unless you have a medical condition. Pain is just the stimulation of pain nerves and doesn't necessarily indicate harm.