11.1 Brain and Food Lecture Questions

Leptin is a hormone that signals energy sufficiency.

• Produced by: Fat cells (adipocytes)

• Sensor location: Hypothalamic nucleus arcuatus (ARC)

Ghrelin is a hunger hormone that signals the need to eat.

• Produced by: Stomach wall (mainly when empty)

• Sensor location: Hypothalamic nucleus arcuatus (ARC)

1. NPY/AgRP neurons

   • Activated by ghrelin / low leptin

   • Stimulate feeding and inhibit energy expenditure

2. POMC/CART neurons

   • Activated by leptin / insulin

   • Suppress feeding and increase metabolism

1. Stomach distension → signaled via vagus nerve

2. Cholecystokinin (CCK) → released by the intestine after fatty meals

(Others include insulin, GLP-1, and peptide YY)

With frequent exposure, the brain becomes less sensitive to the reward.→ The reward threshold increases, and more food (or drug) is needed to achieve the same pleasurable effect.

• PKC delta cells: Detect aversive/bad food, suppress feeding

• Htr2a cells: Promote appetitive behavior, enhance feeding

1. Serotonin (5-HT): Often increased, linked to inhibition and anxiety

2. Dopamine (DA): Often reduced, linked to reduced reward and motivation

1. Binge Eating Disorder (BED): Recurrent overeating without purging

2. Bulimia Nervosa: Binge episodes followed by purging (vomiting, laxatives, etc.)

The hypothalamus is the central hub for body homeostasis.It integrates hormonal, sensory, and neural inputs to regulate hunger, temperature, thirst, and energy balance.

The body uses leptin, a hormone from fat cells, to signal fat stores to the hypothalamus.

• High leptin: signals energy sufficiency → suppresses hunger, increases metabolism

• Low leptin: signals energy need → increases hunger, reduces metabolism This helps maintain body fat around a set point (homeostasis)

Your empty stomach releases ghrelin, a hunger hormone.Ghrelin travels via the bloodstream and activates neurons in the arcuate nucleus (ARC) to trigger hunger.

Your body sends multiple satiety signals:

• Stomach stretch (gastric distension) → via the vagus nerve

• CCK (cholecystokinin) → released from the intestine

• Insulin → from the pancreas in response to glucose

• GLP-1 and PYY → gut hormones that further reduce appetite These signals act on the hypothalamus and brainstem to suppress further food intake.

1. Orbitofrontal cortex (OFC) – assesses reward value

2. Ventral striatum / nucleus accumbens – motivation and "wanting"

3. Amygdala – emotional response to food

4. Insula – taste, interoception

5. Prefrontal cortex – decision-making and control over desire

• repeated exposure to highly palatable food causes the reward system to adapt: → The brain's reward threshold increases → food feels less rewarding

• As a result, individuals eat more of the same food to reach the same pleasure level → this can lead to overeating and obesity

a) Anorexia nervosa → An eating disorder marked by restricted food intake, intense fear of gaining weight, and a distorted body imagedespite being underweight.

b) Binge Eating → Recurrent episodes of eating large amounts of food in a short time, with loss of control and no compensatory behavior (e.g., no purging).

c) Bulimia nervosa → Episodes of binge eating followed by compensatory behaviors like vomiting, fasting, or excessive exercise to avoid weight gain.