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Motivation
 

Motivation

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    Motivation Motivation Presentation Transcript

    • Motivation and Homeostasis The Role of the Hypothalamus
    • Motivation
      • Motivation is the driving force in behavior
      • The stronger the motivation, the more likely the behavior
      • Control of behavior involves decisions among different motivated actions with different outcomes
      • Motivation for behaviors basic to survival is controlled by the hypothalamus
    • The Hypothalamus & Homeostasis
      • Responds to departures from ideal in homeostasis
      • Humoral response
        • hypothalamic neurons respond to inputs from sensors by increasing or decreasing the release of pituitary hormones into blood stream
      • Visceromotor response
        • hypothalamic neurons respond to inputs from sensors by adjusting the balance between the sympathetic and parasympathetic output of the ANS
      • Somatic motor response
        • hypothalamic neurons, especially in the lateral hypothalamus, respond to inputs from sensors by causing a somatic motor response
      • Very often all three happen together or sequentially
    • Regulation of Feeding Behavior
      • Energy balance regulates feeding
      • Hormonal and hypothalamic regulation of body fat and feeding
    • Feeding & Energy Balance
      • Prandial state
        • after eating a meal
      • Postabsorptive state
        • fasting times between meals
      • Obesity occurs when there is consistently more intake than usage and adipose cells enlarge and increase in number
      • Starvation occurs when there is consistently less intake than usage and loss of fat tissue occurs
      • In virtually all mammals except humans and their pets, homeostatic mechanisms act to avoid both obesity and starvation
    • The Prandial State
      • Occurs after eating a meal
      • Glucose, fatty acids, and ketones are produced for all cells; neurons only use glucose
      • Excess energy is stored, either as glycogen in the liver and skeletal muscles, or as triglycerides in adipose tissue = fat cells
      • Anabolism is the assembly of glycogen and triglycerides from what you eat
      • Because the storage capacity for glycogen is limited, excess energy is stored as fat
    • The Postabsorptive State
      • Fasting times between meals
      • Energy is produced from glycogen and triglycerides
      • Catabolism is the process of breaking down glycogen and triglycerides and making glucose, fatty acids, and ketones
    • Hormonal Regulation of Feeding
      • Lipostatic hypothesis
        • The brain monitors the amount of body fat and acts to keep it constant
        • Basically true
      • Adipocytes release leptin into blood
      • Neurons in the periventricular zone of hypothalamus detect a drop in leptin levels
      • Neurons in the lateral hypothalamus are then excited and drive feeding behavior
    • Elevated Leptin & Feeding
      • From 'holiday feasting' for example
      • Leptin receptors on neurons in the arcuate nucleus are activated
      • These neurons use two peptide transmitters:
        • aMSH and CART
      • Response is three-part, triggered by nerve fibers leaving the arcuate nucleus
    • The Response
      • Humoral response is through the paraventricular nucleus
        • Leads to increased release of TSH and ACTH
        • both of which serve to raise the metabolic rate
      • Visceromotor response is to activate the sympathetic division of ANS
        • increases the metabolic rate, partly by raising body temperature.
        • occurs both directly because of activity of arcuate nucleus outputs and through the paraventricular nucleus outputs to the spinal cord
      • Somatic motor response is to inhibit feeding behavior through the neurons of the lateral hypothalamic area
    • Lowered Leptin & Feeding
      • Turns off arcuate nucleus neurons that use aMSH and CART as transmitters
      • Turns on other arcuate nucleus neurons that use NPY and AgRP as transmitters
      • These neurons have connections with the paraventricular nucleus and the lateral hypothalamic area
      • Inhibit secretion of TSH and ACTH
      • Activate the parasympathetic division of ANS
      • Stimulate feeding behavior
    • Key Neurotransmitters
      • aMSH and CART
        • depress feeding behavior
        • therefore called anorectic peptides
      • NPY and AgRP
        • stimulate feeding behavior
        • therefore called orexigenic peptides
    • Role of the Lateral Hypothalamus
      • Some neurons in the lateral hypothalamic area receive direct input from the arcuate nucleus neurons
        • These use the peptide transmitter, MCH
        • MCH neurons innervate most of the cerebral cortex
      • Other neurons in the lateral hypothalamic area also receive direct input from the arcuate nucleus neurons
        • Use the peptide transmitter, orexin.
        • Orexin neurons also innervate most of the cerebral cortex
      • So, when leptin levels fall, there is a major system to drive feeding behavior!
    • Regulation of Feeding Behavior
      • Starting a meal:
      • Cephalic phase
        • sight and smell of food activates the parasympathetic and enteric divisions of the ANS
        • saliva is secreted in the mouth and digestive juices, in the stomach
      • Gastric phase
        • the cephalic phase responses are intensified by chewing, swallowing, and filling the stomach with food
      • Intestinal phase (or substrate phase)
        • As the filling stomach begins to empty in to the intestines, satiety signals arise to stop feeding
    • Satiety
      • Ending a meal
      • Gastric distention
        • mechanoreceptors in the stomach wall connect to the nucleus of the solitary tract via the vagus nerve and inhibit eating
      • The gustatory nucleus is part of the nucleus of the solitary tract, which is why great food can override signals from a full stomach and lead to a totally bloated stomach
    • Cholecystokinin (CCK)
      • Released from neurons in the enteric nervous system and other cells lining the intestines
      • Triggered in response to stimulation of intestines by fatty foods
      • Acts on sensory receptors connected to the vagus nerve and signals to stop eating
    • Insulin
      • Pancreatic cells produce insulin necessary to transport glucose into all cells except neurons
      • Directly affects neurons in arcuate nucleus and ventromedial nucleus of the hypothalamus
        • similar to leptin
      • Late in the eating stage, rising insulin is a satiety signal
    • The Role of Dopamine
      • Liking food and wanting food are mediated by two different systems
      • Wanting food is driven by the mesocorticolimbic dopamine system
      • Animals with lesions in this system still have the hedonic experience (like food), but seem unmotivated to want it
      • Cravings that lead to addiction involve the same dopamine system
    • Drinking
      • Water, not alcohol
      • Two different drives for drinking
        • use two different mechanisms
      • Decrease in blood volume drives drinking
      • Increase in the concentration of solutes in the blood, blood osmolarity, drives drinking
    • Volumetric Thirst
      • Decreased blood volume drives magnocellular neurons in the hypothalamus
        • release ADH
        • leads to concentrated urine
        • humoral response
      • Decreased blood volume stimulates the sympathetic division of the ANS
        • helps to correct low blood pressure
        • visceromotor response
      • Decreased blood volume stimulates neurons in the lateral hypothalamus
        • drives seeking and consuming water
        • somatic motor response
    • Osmometric Thirst
      • Hypertonicity of the blood is sensed by vascular organ of the lamina terminalis (OVLT)
        • outside the blood brain barrier just like the subfornical organ
      • OVLT cells when excited, directly drive magnocellular neurons to release ADH
        • humoral response
      • Hypertonicity drives the OVLT to stimulate the motivation to drink water through the lateral hypothalamic area
        • somatic motor response
    • Diabetes Insipidus
      • One type of diabetes includes failure to release ADH
      • Caused by loss of magnocellular neurosecretory neurons in hypothalamus, or viral infection of hypothalamus
      • ADH is not secreted, urine is very dilute
      • Osmometric thirst drives patients to drink vast amounts of water
      • Vast amounts of urine are passed
      • Patients become sorely sleep deprived - dangerous
      • Synthetic ADH can be administered nasally
    • Temperature Regulation
      • In addition to the somatosensory thermal receptors, there are lots of neurons in the brain sensitive to temperature.
      • Most important cluster is in the anterior hypothalamus
        • monitors blood temperature
      • Humoral and visceromotor responses are then initiated by the medial preoptic area of the hypothalamus
      • Somatic motor responses are initiated by the lateral area of the hypothalamus
    • Decreasing Temperature
      • A fall in temperature in the blood leads to:
      • Humoral response
        • TSH is released by the anterior pituitary causing:
        • thyroxin release by the thyroid gland
        • increases cellular metabolism and produces heat
      • Visceromotor response
        • constricted blood vessels near the skin surface and piloerection (goose bumps)
      • Somatic motor response
        • involuntary shivering
        • voluntary action to seek warmth
    • Increasing Temperature
      • A rise in temperature in the blood leads to:
      • Reduction of TSH release
        • humoral response
      • Blood is shunted toward surface capillary beds
        • visceromotor response
      • Animal seeks shade
        • voluntary somatic motor response
      • Animal pants or humans sweat
        • involuntary somatic motor response