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Motivation and Regulation of the Internal States

Motivation and HomeostasisMotivation literally means to set in motionPsychologists were not able to define it solely in terms of external stimuli. There various kinds of motivation such as achievement or hunger.Motivation is a concept psychologists invented. Do not expect to find a motivation center in the brain.

Theoretical Approaches to MotivationInstinct : it is a complex behavior that is automatic and unlearned and occurs in all the members of a species Example: Maternal instincts or migration in animals.At any rate we need to be extremely careful about how we use the term instinct and to avoid the temptation to label any behavior that is difficult to explain as an instinct.

The drive theory has fared much better in explaining motivation than the instinct theory

Drive: the body maintains a condition of homeostasis in which any particular system is in balance or equilibrium. Any departure from homeostasis such as depletion of nutrients or drop in temperature causes an aroused condition or Drive

Simple Homeostatic DrivesTemperature regulationIn mammals the major thermostat is located in the preoptic area of the hypothalamus, which contains warmth-sensitive and cold-sensitive cells directly to the temperature of the blood flowing through the areas

Others receive input from temperature receptors in other parts of the body, including the skin.The preoptic area ofThe brain integratesRegulatory responsesSuch as sweating,Panting, or shivering.

ThirstWater is needed to maintain the cells of the body to keep the blood flowing through the veins and arteries and to digest food.There are two types of thirst:Osmotic thirstHypovolemic thirst

Osmotic thirstThis occurs when the fluid content decreases inside the cells. This happens when the blood becomes more concentrated than usual, usually because the individual has not taken in enough water to compensate for food intake.This is detected by the bordering third ventricle particularly in the organum vasculosum lamina terminalis or OVLT

Hypovolemic thirstThis occurs wen the blood volume drops due to a loss of extracellular water. This can be due to sweating, vomiting, and diarrhea.Hypovolemia is detected by receptors located where the large veins enter the atrium of the heart.

HungerEating provides energy for activity, fuel for maintaining body temperature, and materials needed for growth and repair of the tissues. The set point is varies with demands on our resources caused by exercise, stress, growth and so on.

The role of tasteTaste receptors are located on taste buds which in turn are found on the surface of the papilla.Besides the 4 primary tastes the newest one added is called umami.

The taste neurons travel through the thalamus to the insula, the primary taste area in the frontal lobes, but on their way they pass through the medulla.Each of the primary taste stimuli is detected by receptors that are specialized for that stimulus .Information from the different receptors travels to the brain via separate pathways to distinct areas in the insular cortex.

The taste sense contributes to dietary selection in three additional ways:Sensory specific satietyLearned taste aversionLearned taste preferences

Sensory-specific satiety

This means that the more of a particular food an individual eats, the less appealing the food becomes.

The effect sounds trivial but it is not; Sensory-specific satiety is the brains way of encouraging you to vary your food choices, which is necessary for a balanced diet.

Learned taste aversionLearned taste aversion is the avoidance of foods associated with illness or poor nutrition.Learned taste aversion helps wild animals and primitive-living humans avoid dangerous foods.

Learned taste preferencesThis is the preference for the flavor of a food that contains a particular nutrient.Taste: the experience you get from your taste receptorsFlavor: depends on the combination of taste and smell.

The digestive process

Digestion begins in the mouth where food is ground and mixed with saliva.After reaching the stomach it mixes with HCL and if the food is not favorable the stomach responds by regurgitating it.If the toxins make their way into the blood stream, the postrema in the brain induces vomiting.

Digestion primarily occurs in the duodenum where the food is broken down into usable forms. CarbohydratesProteinsFatsThe products of digestion are absorbed through the intestinal wall and transported to the liver via the hepatic portal vein This process is under the control of the autonomic nervous system

Simple sugars such as glucose

Converted into amino acids

fatty acids and glycerol

The Two Phases of MetabolismThe absorptive phase: For a few hours following a meal, the body lives off the nutrients arriving from the digestive system.

The fasting phase: Eventually the glucose level in the blood drops. Now the body must fall back on its energy stores, which is why it is called the fasting phase.

Signals That Start a MealDid you know that the stomach is not necessary to feel hunger?There are three major signals for hunger:Glucoprivic hunger : tells the brain there is a low supply of glucose.Lipoprivic hunger: indicates a deficit in fatty acidsInforms us that the stomachs store of nutrients has been depleted.

The role of GhrelinIt is part of the third major signal for hunger. It is synthesized in the stomach and released into the bloodstream as the stomach empties during fasting . Signals of glucose and fatty acid deficits are carried by the vagus nerve from the liver to the NST(Pg. 171) in the medulla.

Three of these hunger signals exert their influence through neurons in the arcuate nucleus which excite the lateral hypothalamus and increase eating and reduce metabolism.

Signals That End a MealJust as with drinking there must be a satiety mechanism that ends a mean well before nutrients reach the tissues.Optimal satiation requires the interaction of mouth, stomach, and intestinal factors. The best known of these satiety signals is Cholecystokinin (CCK), a peptide hormone released as food passes into the duodenum.

Long term controlsOver long periods humans and animals regulate their eating behavior by monitor in their body weight or more precisely their body fat but how they do it is unclear.How much we eat at a meal is also regulated by the amount of fat we have stored indicated by leptin and insulin levels.

An additional contributor to the control of feeding and body weight is orexin or hypocretin, a neuropeptide that increases appetite and induces eating.

ObesityObesity is measured in BMI (Body mass index)It is calculated by dividing the persons weight in kilograms by the square height in meters.

Obesity is most important because of its health risks. As overweight and obesity increase, so does the incidence of diabetes.

Obesity increases the likelihood of high blood pressure, heart disease, stroke and colon cancer. Obesity is also linked to cognitive decline and risk for Alzheimers diseases

Myths of obesitySimply put the cause of obesity is energy in exceeds energy out.#1 caused by inability to control appetite.#2 Inability to delay gratification#3 Maladaptive eating styles#4 It runs in the familyObesity does run in families and it is moderately to family members but research shows that environmental effects are stronger

All the known genes account for only a small proportion of obesity, and heritability measures leave room for significant environmental influence. Indeed we must recognize that the recent surge in obesity is due to non-genetic factors such as diet and activity.

Contributions of the heredity and the Environment to obesitySleep deprivation : sleep loss reduces leptin levels and increases ghrelin secretion which makes you crave for high calorie foods.Certain types of infection: Bacteria of the phylum Firmicutes are most likely the culprit. This bacteria can be found in the gut.

Obesity and Reduced MetabolismDifferences in basal metabolism may be a key element in explaining differences in weight. However a persons metabolism can shift when the person gains or loses weight.The energy expenditure changes are greater than the weight changes required, which means the individuals bodies defend their original weight.

So why doesnt this defense of body weight prevent people from becoming obese?The body reserves excess nutrients for a time of starvation.A second reason is that people vary tremendously in the strength of their defense response making some people more vulnerable to being overweight than others.

Treating obesityThe standard treatment for obesity is of course dietary restriction.Another option is medication. But the problem with drugs is that they manipulate metabolic and other important body systems and often have adverse side effects. Drugs such as Belviq and Qsymia are examples are drugs used.

Researchers have also looked into treatment with hormones. The leptin treatment however only benefits 5% to 10% of the obese people who are leptin deficient. The rest of the population are resistant to leptins effects.A more recent therapeutic approach involves treating eating disorders as other addictions. Some drugs used in addiction treatment have shown promise for treating obesity.

Leptin deficiency

The most effective procedure is the gastric bypass. It reduces the stomach to a small pouch which is then reconnected at a lower point on the intestine. This limits the meal size and the nutrient absorption in the digestive tract.

Anorexia, Bulimia and Binge Eating DisordersAnorexiaAnorexia nervosa is known as the starving disease because the individual restricts food intake to maintain weight at a level so low that can be life threatening.If Anorexia continues long enough, it leads to cessation of ovulation, loss of muscle mass, heart damage and reduction in bone density. This is more prevalent among females.

BulimiaBulimia nervosa also involves weight control, but the behavior is limited to bingeing and purging.Binge eating disorderIn this the individual frequently eats large amounts of food during a short period of time and they feel like they cannot control it. They are often obese because they do not attempt to control weight.

CausesMany of these eating disorders, especially in the western society where more emphasis is given on thinness and beauty has been deemed to be an environmental cause of these disorders. Other psychological problems could also trigger disordered eating, starvation or overeating.

The role of Serotonin, Dopamine and CannabinoidsImaging studies indicate that anorexia and bulimia patients have an imbalance activity at Serotonin receptors. These receptors are of interest because of their role in anxiety depression, compulsive behaviors and harm avoidance.Dopamine is associated with lowering anxiety. Because eating increases Dopamine release, this finding lends additional support to the idea that food restriction serves to reduce anxiety.

Cannabinoid Both anorexic and bulimic patients have larger numbers of cannabinoid receptors in the insula whose functions include the rewarding effects of food and responses to hunger.