Introduction to Psychology
Motivation and Control of Action
Prof. Jan Lauwereyns
Homeostasis
Definition – ‘Maintenance of the body’s internal environment within a narrow physiological range’
Internal environment – refers to body temperature and blood compositions
HypothalamusPrimarily involved in maintaining body temperature, fluid and energy homeostasis
Thirst• Water regulation is critical: 70% of body is water
– concentration of chemicals determines rate of reactions
– blood volume must be enough to maintain blood pressure and circulation
• Strategies for regulation– too much: excess water excreted through
urination – too little: vasopressin, anti-diuritic hormone,
constricts blood vessels to increase blood pressure and enables kidneys to reabsorb water and secrete concentrated urine
Energy Balance
Why is it important?Brain needs constant glucose supply
A few minutes glucose deprivation leads to loss of consciousness and death
Hunger
Biological needs
The drive reduction hypothesis
Think: Inclusive fitness (Darwinian processes)
Think: energy, reproduction
Approach
Avoid
Biological needs
Several hours have passed since last meal
Increased drive (hunger)
Increased exploratory activity
Find food, eat it
Drive is reduced (reinforcement)
The drive reduction hypothesis
Biological needs
Several hours have passed since last meal
Find food, eat it
Drive is reduced (reinforcement)
The drive reduction hypothesis
Increased drive (hunger)
Increased exploratory activity
Biological needs
Several hours have passed since last meal
Find food, eat it
Drive is reduced (reinforcement)
The drive reduction hypothesis
Increased drive (hunger)
Increased exploratory activity
Wanting
Liking
When do you start (wanting) a meal?
- Cultural and social factors (habit, copy)
- Physiological factors (hunger)
Eating: Physiological factors
• Fuel for cells:– Glucose (brain)– Fatty acids (rest of the body)
• Glucose in a meal some used for fuel some
converted into glycogen
• The glucostatic hypothesis of hunger
Neurons in the hypothalamus
• Lateral hypothalamus: – Neurons signal hunger (“glucostats”)– When damaged, no hunger, won’t eat, will
starve
Glucose, Insulin and Glucagon• Glucose
– much of digested food enters bloodstream as glucose, primary energy source for cells in body and brain
– remains constant because liver converts stored nutrients to glucose
• Amount of glucose actually available to cells depends on two hormones from pancreas – insulin helps glucose enter cells, decreasing
amount in bloodstream – glucagon stimulates liver to convert glycogen to
glucose, increasing amount in bloodstream
Neurons in the hypothalamus
• Lateral hypothalamus: – Neurons signal hunger (“glucostats”)– When damaged, no hunger, won’t eat, will
starve
• Ventromedial hypothalamus:– Neurons signal satiation– When damaged, never enough, will keep
eating, grow very obese
After a meal insulin levels rise and glucose enters cells, appetite decreases – as glucose levels fall, the pancreas
releases glucagon and less insulin– less glucose for immediate fuel, blood
levels rise and hunger returns
Untreated diabetics eat much but lose weight. Because of their low insulin levels, the glucose in their blood cannot enter the cells, either to be stored or to be used. Consequently, glucose is excreted in their urine, leaving the cells to starve.
• When do we eat more than we need?– when we are with other people– in the evening– on weekends– if food is low-fat– when it tastes good– alcoholic beverages add calories
• Disorders– Anorexia nervosa, bulimia– Hormonal conditions (e.g., leptin)