Neuroscience of Behavior: Homeostasis and Hunger

Homeostasis

The balanced functioning of physiological processes and maintenance of an organism's internal environment within a narrow range.

Stressor

Anything that disrupts homeostasis, including heat, cold, hunger, thirst, threat, or anticipation of an aversive event.

Stress Response (physiological)

Body's adaptations to reestablish homeostasis.

Hypothalamus

Master regulator of body processes including sleep and wakefulness, feeding and energy metabolism, fluid and electrolyte balance, blood composition and volume, stress response, body temperature, heart rate and blood pressure, and reproduction.

Hunger

Motivational state that provokes food intake.

Glucose Homeostasis

Ultimate reason for hunger.

Arcuate nucleus

Central driver of feeding behavior.

⍺MSH/CART neurons

Anorexigenic neurons that suppress food intake.

NPY/AgRP neurons

Orexigenic neurons that stimulate food intake.

Orexin

Hypothalamic peptide that promotes meal initiation.

MCH

Hypothalamic peptide that prolongs consumption.

Exogenous orexin

0.3nmol orexin-A into the hypothalamus increases food intake.

Anticipatory factors

Permissive or influencing factors related to food intake.

Feedback mechanism

Basic regulatory mechanism to maintain homeostasis.

Second-order neurons

Neurons in the hypothalamus that include the paraventricular nucleus (PVN), lateral hypothalamus (LHA), and peri-fornical area (PFA).

Physiological processes

Processes that maintain the internal environment of an organism.

Claude Bernard

Described the regulation of internal environment in 1849.

Walter Bradford Cannon

Coined the term 'homeostasis' in 1926 and 'fight or flight' in 1915.

Joseph Barcroft

Brought the brain into the discussion of homeostasis in 1932.

Influencing factors of hunger

Incentive value of food, time of day, memory of when we ate last, neural and endocrine signals from gut.

Physiological adaptations

Changes in the body to reestablish homeostasis.

Meal initiation

Process promoted by orexin.

Prolonged consumption

Process prolonged by MCH.

Food intake

Behavior influenced by the balance of orexigenic and anorexigenic signals.

Feedback

Mechanism that helps maintain homeostasis.

Physiological processes

Functions that help maintain an organism's internal environment.

Ghrelin

The ONLY GI hormone that induces food intake.

Cholecystokinin (CCK)

An endocrine signal from the small intestine that stops feeding behavior within a meal.

Amylin

A hormone from the pancreas that contributes to within-meal satiety.

Peptide YY (PYY)

An endocrine signal from the large intestine that contributes to between-meal satiety.

Glucagon-like Peptide 1 (GLP-1)

An endocrine signal from the large intestine that contributes to between-meal satiety.

Ozempic

A GLP1 Receptor agonist prescribed to reduce body mass and blood glucose.

Insulin

A hormone critical for glucose accessing non-neuronal body cells and acts as a satiety signal.

Insulin receptor

Required for glucose uptake, except in the brain which has GLUT transporters.

Leptin

A hormone released by fat cells to suppress appetite and increase energy expenditure.

Leptin-deficient mice

Mice that lack leptin and thus have uncontrolled appetite.

Lipostatic hypothesis

The theory that long-term regulation of food intake is governed by blood concentration of free fatty acids.

Leptin receptors

Regulate the activation of first-order NPY/AgRP and POMC/CART neurons in the arcuate nucleus.

Thyroid Hormone Regulation

High levels of leptin stimulate TSH release and increase metabolism.

Thermogenesis

The process of heat production in organisms, promoted by high levels of leptin.

Energy Balance

The state where energy intake equals energy expenditure, influenced by many factors beyond calories.

NPY/AgRP neurons

Orexigenic neurons that promote meal initiation.

POMC/CART neurons

Anorexigenic neurons that regulate consumption.

Orexin

A hypothalamic peptide that promotes meal initiation.

MCH

A hypothalamic peptide involved in energy balance.

CCK

An endocrine signal that contributes to within-meal satiety.

GLP-1

An endocrine signal that contributes to between-meal satiety.

Within-meal satiety

The feeling of fullness that occurs during a meal.

Between-meal satiety

The feeling of fullness that occurs between meals.

Ghrelin

A GI hormone that induces food intake.

Long-term energy balance

Regulated by hormones that signal first-order hypothalamic neurons.

Activation of ARC GLP-1R neurons

Does NOT regulate blood glucose and insulin secretion.