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Mind, Brain & Behavior
Friday
March 7, 2003
Diffuse Enteric System
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A third major division of the autonomic
nervous system.
Neural control unit between the autonomic
postganglionic nerves and the gastrointestinal
system.
Contractions of muscles propels food through
digestive system (peristalsis).
Central Regulation (CNS)
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Hypothalamus – integrates visceral
functioning:
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Activates the autonomic nervous system
Regulates hormones secreted from the pituitary
gland and thereby controls the endocrine system.
Three Parts of Hypothalamus
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Periventricular Zone – regulates temperature,
salt concentration, levels of hormones.
Medial Zone – produces vasopressin and
oxytocin in posterior pituitary.
Lateral Zone – permits cortex and limbic
system to over-ride hypothalamic activity,
manages long-term regulation.
Medulla Oblongata
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Responsible for monitoring:
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Spontaneous respiratory movement (breathing)
Blood pressure
Cardiac rhythm
“Brain death” occurs with loss of
hypothalamic and medullary control over
respiration, lack of EEG waves.
Endocrine System
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Endocrine organs include:
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Pituitary gland
Adrenal Cortex
Gonads (ovaries and testes)
Thyroid and parathyroid
Adrenal cortex
Islet cells of pancreas
Secretory cells that line intestinal tract
Physiological Setpoints
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Adaptive systems use feedback from sensors
to maintain constant values (setpoints) for
important properties.
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Positive feedback activates a central controller
Negative feedback inhibits the controller.
Temperature Regulation
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Two controls:
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Sensors from skin
Blood temperature (at hypothalamus)
Heat-gain mechanisms increase blood
temperature (goose bumps).
Heat-loss mechanisms decrease it (shunt
blood to skin, perspiration).
Purpose of Fever
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Occurs when immune response causes heatgain mechanisms to increase body
temperature.
Elevated temperature:
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Activates antibody-producing cells
Increases the rate at which white blood cells
move to sites of infection.
Directly affect some viruses but not all.
Blood Pressure
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Pressure or baro-receptors measure pressure
in the large arteries above the heart.
Excess pressure activates the medulla
oblongata:
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Excess sympathetic activity depressed.
Inhibition of vasomotor centers (which expand
and contract blood vessels).
High Blood Pressure
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Ongoing competition between sympathetic
and parasympathetic.
Setpoints are too high in people with chronic
high blood pressure.
Causes include:
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Kidney disease
Overactive sympathetic system.
Appetite Control
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Motivation to eat arises from a complex
interplay of physiological mechanisms.
Two systems involved:
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Metabolic need system – restore depleted energy
Caloric homeostasis system – eat when food is
available until stomach is distended.
Setpoint Hypothesis of Eating
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Adiposity (fat storage) may be a regulator of
eating behavior.
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The brain directs metabolic processes to maintain
its fat store.
Insulin signals status of fat stores to the brain.
Adiposity affects insulin secretion.
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Lean people are more sensitive to insulin so more
carbohydrate is used and does not become fat.
Control of Food Intake
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Hyperphagia – overeating to obesity.
Aphagia – severe abstinence, resulting in
death unless an animal is force-fed.
Lateral or medial hypothalamic lesions affect
food intake – interruption of fibers of passage.
Food intake is also controlled by sensory
information, alteration of set-point, hormonal
balance.
Cues Regulating Hunger
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Short-term:
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Chemical properties of the food
Gastrointestinal and liver feedback signaling
satiety.
Long-term:
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Signal reflecting body weight and fat storage.
Satiety Factors
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Stretch receptors signal “fullness” to prevent
overfilling of the stomach.
Digestive hormones secreted in the gut signal
satiety.
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Manipulation of these hormones can change
eating behaviors and weight in mice.
Psychological Factors
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Learned associations with time and place.
Socialization and rituals associated with food
(e.g., eating at a party).
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People eat more when in social situations.
Preferences and taste
Eating Disorders
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Anorexia Nervosa – deliberate starvation due
to psychological factors.
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Insufficient body weight
Distorted body image, food obsession
Anorexics have normal appetite
Bulimia Nervosa – food binging followed by
purging with laxatives or vomiting.
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Normal body weight
Obesity
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Based on height and weight, a body mass
index above 30 (above 25 is overweight).
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Causes:
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http://www.caloriecontrol.org/bmi.html
Different metabolic rate
Larger adipocytes
More vulnerable to food cues, finicky
Recidivism after dieting = 90+% in all forms
of treatment.