Mind, Brain & Behavior Friday March 7, 2003

Diffuse Enteric System  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)  Hypothalamus – integrates visceral functioning: Activates the autonomic nervous system Regulates hormones secreted from the pituitary gland and thereby controls the endocrine system.

Three Parts of Hypothalamus  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  Responsible for monitoring: 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  Endocrine organs include: 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  Adaptive systems use feedback from sensors to maintain constant values (setpoints) for important properties. Positive feedback activates a central controller Negative feedback inhibits the controller.

Temperature Regulation  Two controls: 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  Occurs when immune response causes heat- gain mechanisms to increase body temperature.  Elevated temperature: 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  Pressure or baro-receptors measure pressure in the large arteries above the heart.  Excess pressure activates the medulla oblongata: Excess sympathetic activity depressed. Inhibition of vasomotor centers (which expand and contract blood vessels).

High Blood Pressure  Ongoing competition between sympathetic and parasympathetic.  Setpoints are too high in people with chronic high blood pressure.  Causes include: Kidney disease Overactive sympathetic system.

Appetite Control  Motivation to eat arises from a complex interplay of physiological mechanisms.  Two systems involved: Metabolic need system – restore depleted energy Caloric homeostasis system – eat when food is available until stomach is distended.

Setpoint Hypothesis of Eating  Adiposity (fat storage) may be a regulator of eating behavior. The brain directs metabolic processes to maintain its fat store.  Insulin signals status of fat stores to the brain.  Adiposity affects insulin secretion. Lean people are more sensitive to insulin so more carbohydrate is used and does not become fat.

Control of Food Intake  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  Short-term: Chemical properties of the food Gastrointestinal and liver feedback signaling satiety.  Long-term: Signal reflecting body weight and fat storage.

Satiety Factors  Stretch receptors signal “fullness” to prevent overfilling of the stomach.  Digestive hormones secreted in the gut signal satiety. Manipulation of these hormones can change eating behaviors and weight in mice.

Psychological Factors  Learned associations with time and place.  Socialization and rituals associated with food (e.g., eating at a party). People eat more when in social situations.  Preferences and taste

Eating Disorders  Anorexia Nervosa – deliberate starvation due to psychological factors. Insufficient body weight Distorted body image, food obsession Anorexics have normal appetite  Bulimia Nervosa – food binging followed by purging with laxatives or vomiting. Normal body weight

Obesity  Based on height and weight, a body mass index above 30 (above 25 is overweight).  Causes: Different metabolic rate Larger adipocytes More vulnerable to food cues, finicky  Recidivism after dieting = 90+% in all forms of treatment.