GSU NEUR 3000 - NEUR 3000 - Chapter 16 (26 pages)

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NEUR 3000 - Chapter 16



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NEUR 3000 - Chapter 16

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Pages:
26
School:
Georgia State University
Course:
Neur 3000 - Hon Principles of Neuroscience
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MOTIVATION NEUR 3000 Dr Joseph J Normandin WHAT IS MOTIVATION Voluntary actions are produced to satisfy a need This need can be abstract I need to go hiking in a Massachusetts forest Here the motivation is hard to describe This need can be concrete I need to eat Here the motivation is easy to describe I feel hungry Motivation drives behavior in a way that a particular behavior is more likely to occur We have yet to develop a full concept of why we might want to go hiking but we do have an understanding of many of the motivations necessary for survival THE HYPOTHALAMUS HOMEOSTASIS MOTIVATED BEHAVIOR Recall that the hypothalamus has been described as a regulator of homeostasis In a sense the basic needs for survival body temperature fluid balance energy balance Hypothalamic regulation begins with sensory transduction A regulated parameter must be measured by sensory neurons e g temperature Periventricular hypothalamic neurons detect that this is outside the normal range Hypothalamic neurons then orchestrate the body s response Humoral response stimulating or inhibiting pituitary hormone release into the blood LONG TERM REGULATION OF FEEDING BEHAVIOR The brain needs energy in the form of glucose as much as it needs oxygen A few minutes of glucose deprivation leads to unconsciousness Because food availability is not assured the body has evolved a number of mechanisms to store energy and use it when needed We have also evolved the motivated behavior to seek out food to keep our energy stores full LONG TERM REGULATION OF FEEDING BEHAVIOR LONG TERM REGULATION OF FEEDING BEHAVIOR LONG TERM REGULATION OF FEEDING BEHAVIOR The lipostatic hypothesis The brain monitors amounts of body fat and acts to maintain body fat LONG TERM REGULATION OF FEEDING BEHAVIOR The lipostatic hypothesis The brain monitors amounts of body fat and acts to maintain body fat In order for this to occur there must be some communication between body fat and the brain LONG TERM REGULATION OF FEEDING BEHAVIOR The lipostatic hypothesis The brain monitors amounts of body fat and acts to maintain body fat In order for this to occur there must be some communication between body fat and the brain Leptin is secreted by adipocytes and acts on the hypothalamus to decrease appetite and increase energy expenditure Leptin deficiency i e low body fat stimulates hunger suppresses energy expenditure and inhibits sexual behavior LONG TERM REGULATION OF FEEDING BEHAVIOR The hypothalamus and feeding In rats bilateral lesions of the lateral hypothalamus produce anorexia decreased appetite Bilateral lesions of the ventromedial hypothalamus produce overeating Also occurs in humans with brain damage to these regions LONG TERM REGULATION OF FEEDING BEHAVIOR Leptin and the hypothalamus Leptin released by adipocytes binds to leptin receptors in the arcuate nucleus of the ventromedial hypothalamus Arcuate neurons contain the neuropeptides MSH CART Arcuate neurons project to different parts of the nervous system to orchestrate the body s response to high leptin Projections to paraventricular nucleus Humoral response CRH TRH increase metabolism Visceromotor response activate sympathetic ANS Projections to spinal cord LONG TERM REGULATION OF FEEDING BEHAVIOR LONG TERM REGULATION OF FEEDING BEHAVIOR Leptin and the hypothalamus A fall in leptin levels activates other neurons in the arcuate nucleus These arcuate neurons contain the neuropeptides NPY AgRP Arcuate projections from these neurons produce effects opposite those of MSH CART Projections to paraventricular nucleus Humoral response No CRH TRH no increase in metabolism Visceromotor response activate parasympathetic nervous system Projections to lateral hypothalamus LONG TERM REGULATION OF FEEDING BEHAVIOR LONG TERM REGULATION OF FEEDING BEHAVIOR LONG TERM REGULATION OF FEEDING BEHAVIOR The lateral hypothalamus Leptin sensitive arcuate neurons project to specific types of neurons in the lateral hypothalamus Neurons containing the neuropeptide MCH Widespread projections to cerebral cortex In rats injection of MCH stimulates feeding behaviors Neurons containing the neuropeptide orexin Widespread projections to cerebral cortex In rats injection of orexin stimulates feeding behaviors SHORT TERM REGULATION OF FEEDING BEHAVIOR Short term regulation of feeding is related to The motivation to eat since our last meal The motivation to continue eating stop eating once we have started The phases of feeding Cephalic phase Sight and smell of food triggers a number of physiological responses Parasympathetic and enteric ANS are activated Saliva and gastric juices are secreted Gastric phase As you began eating these responses intensify SHORT TERM REGULATION OF FEEDING BEHAVIOR Appetite eating digestion satiety Feeling hungry appetite signals When the stomach is empty it produces a peptide called ghrelin which is released into the bloodstream Ghrelin activates the NPY and AgRP containing neurons of the arcuate Consequence SHORT TERM REGULATION OF FEEDING BEHAVIOR Appetite eating digestion satiety Feeling full satiety signals Stretching of the stomach wall Mechanosensory neurons ascend via the vagus nerve CN X to the nucleus of the solitary tract Inhibits feeding The peptide cholecystokinin CCK is released when the intestines sense fatty foods CCK activates vagal nerve sensory neurons SHORT TERM REGULATION OF FEEDING BEHAVIOR Appetite eating digestion satiety Feeling full satiety signals Insulin Insulin allows cells of the body to metabolize glucose Maximal insulin release occurs during the substrate phase Insulin levels act directly on the arcuate hypothalamus to produce satiety and inhibit feeding Which arcuate neurons would you expect to have a high expression of insulin receptors WHY DO WE EAT We eat because we are hungry and eating reduces hunger This satisfies the drive to eat We can think of this as wanting food We also eat because food tastes good and it makes us feel good This aspect of motivation is termed hedonic it gives us pleasure We can think of this as liking food How are liking and wanting processed in the REWARD REINFORCEMENT Clues to wanting and liking were first found in studies of electrical self stimulation in rats Rats will selfstimulate if the electrode is placed in a part of the brain that provides a good feeling or reward REWARD REINFORCEMENT The reward systems of the brain includes the projections from the ventral tegmental region of the midbrain Dopaminergic neurons Injection of DA


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