Week 8: Hunger and the Chemical Senses

Glucose

Molecule important for keeping our body functional via energy, also the preferential energy source of the brain

High = satiated

Low = Hunger

Glycogen

Body storage for glucose, released in between meals to give your body energy when there is not a readily available source of glucose, stored in the muscles and liver

High = Satiated

Low = Hunger

Insulin

Secreted by pancreas, promotes uptake and use of glucose by cells and storage of glucose as insulin, with excess turned to adipose

High = Satiated

Low = Hunger

Neuropeptide Y

Stimulates the hypothalamus for increased appetite and food seeking behaviors during low glycogen levels

High = Hunger

Low = Satiated

What are 3 signals of fullness in the body?

1. Stretch receptors signal stretch of stomach when food is present via vagus nerve

2. Digestive hormones (CCK) released in GI tract when full

3. High glucose/glycogen levels detected by liver

Cholecystokinin

Released by small intestine present in stomach, detected by brain receptors to stop eating in the short-term (to end a meal)

High = Satiated

Low = Hunger

Adipose

Storage of excess energy in the long term for use when food is scarce. More energy dense than glycogen, thus a more efficient method of energy storage than glycogen

Leptin

Secreted by adipose, involved in long term energy balance, stimulates hypothalamus and receptors to reduce appetite and food consumption with increased adipose by inhibiting the NPY hormone

High = satiated

Low = hunger

OB Gene

Controls leptin production

Does increased leptin cause weight loss in humans?

No, increased leptin causes leptin resistance instead of weight loss, which reduces leptins ability to inhibit appetite

What does increased NPY levels cause in rats?

1. Higher sucrose intake

2. Higher saccarin

3. Prefer carbs over fats and protein

4. Willing to work more for carbohydrates

Endogenous Opioids

Naturally occurring chemical substances that have morphine-like analgesic actions in the body, and contributes to platability and reward=driven feeding

What are two possible theories of overeating behavior present in humans?

1. Genetic predisposition for greater preference for carbs due to amplified NPY levels

2. Maladaptive opioids (increased opioids) may cause greater reward-driven feeding behaviors

Does our body have more defensive mechanisms for excessive weight gain or weight loss?

Excessive weight loss

Evolutionary desire to eat food for survival

What are two universal taste preference characteristics observed in infants?

1. All infants display the same facial expressions to a particular taste

2. Infants with hydrocephalus (a type of brain damage) and health infants both react the same to taste

What does universal taste preferences in infants suggest about the brain regions in which taste is processed?

Most likely generated by lower/older brain structures

What taste differences are observed between males and females?

Females have greater sensitivity to sweet and bitter tastes, especially in the 1st trimester during pregnancy (greater need to avoid toxins)

What does a sweet taste signify?

High in sugar/carbohydrates/energy (Preferred)

What does a sour taste signify?

Presence of acids, spoiled food (Not preferred)

What does a umami taste signify?

Presence of aspartate and glutamate amino acids (Preferred)

What does a salty taste signify?

Presence of electrolytes, needed for neurological function (Preferred)

How many taste receptors are there on a single taste bud?

50-150

Taste buds

Structures in the mouth, 2/3rds of which are located on the tongue, which contains taste receptors that process all 5 different flavors

Gustatory cortex

Responsible for perceiving all 5 tastes from the taste receptors

Relays taste signals through two pathways

1. Primary somatosensory -> taste processing

2. Orbital cortex -> flavor processing

What is the role of the primary somatosensory cortex in taste processing?

Processes texture of food

What is the role of the orbital cortex in taste processing?

Combines smell and taste to process flavors

What is the role of the amygdala in taste processing?

Triggers satiety via CCK and emotional processing of food (yummy food = :))

Which sensory modality does not get processed by the thalamus?

Smell

What is the taste processing pathway in the brain, from the taste buds to the cortexes?

Taste buds -> Taste receptors -> Medulla -> Thalamus -> Gustatory Cortex/Hypothalamus -> GC=Primary Somatosensory, Orbital Cortex; Hypo=Amygdala

What is the smell processing pathway in the brain, from the nose to the cortexes?

Nose -> Nasal pharynx -> Olfactory Cilia/Olfactory Epithelium -> Olfactory bulb -> Glomeruli -> Primary Olfactory Cortex; Limbic System; Orbital Cortex

Olfactory Cillia

Tiny hair structures that cover receptor surface of nasal cavity

Olfactory Epithelium

Receptor surface of nasal cavity, contains olfactory cilia

Olfactory Bulb

Location where olfactory receptor cell axons synapse with the glomeruli

Glomeruli

Neurons that receive signals from the olfactory receptors cells and relay it to higher structures in the cortex, namely the primary olfactory cortex, limbic system, and orbital cortex

How are spicy tastes processed in the mouth?

Capsaicin from spices triggers heat and pain receptors in the mouth

How many receptor(s) are activated by 1 smell?

1 smell activates multiple/pattern of smell receptor cells

How many receptor(s) are activated by 1 taste?

1 taste = 1 receptor

What is the role of the hypothalamus in hunger? (txt)

Part of the brain responsible for producing feelings of hunger and satiety

What 3 actions does ghrelin have in the body? (txt)

1. Stimulates hypothalamus for hunger

2. Increases gastric motility (rumbling stomach, hunger pangs)

3. Positive effect on learning

What are 3 satiety cues of the body? (txt)

1. Increased stomach stretching

2. Increased release of CCK (causes hypothalamus to process satiety and slow down motility of stomach)

3. Increased nutrients in the portal veins

Are liquid or solid foods less satiating? Why? (txt)

Liquid foods are less satiating than solid foods since they cause less stomach stretch and are absorbed faster, which causes less CCK to be released during digestion

What effect does stress have on appetite? (txt)

Acute response - SNS response, causes decreases in appetite

Slow response - release of glucocorticoids, which increases appetite (source of stress eating)

Gustatory neuron (txt)

Neuron that generates an AP in response to NTs released by taste cells, which is carried to the gustatory cortex of the medulla

What 3 brain structures does the glomeruli relay smell signals to, and what does each structure do? (txt)

1. Orbital cortex (processes flavor by combining smell and taste info)

2. Amygdala (processes emotion)

3. Hippocampus (processes strong memory of smell)

What was observed in rats that had unlimited access to high carbohydrate food? (Lec)

Rats that had unlimited access to high carb foods engaged in very healthy levels of eating, even willing to be shocked to eat

Observed higher levels of dopamine in brain (food addiction may be similar to drug addiction)

What are "blue zones" in terms of healthy eating? (Lec)

Healthier zones, where people have a more natural diet and perform more physical activity. They also have strong social networks, which allow them to have longer dinners (conversation while eating)

What was observed in babies born after the Winter Hunger in the Netherlands? (Lec)

Greater rates of obesity, diabetes, and cardiovascular disease due to possible increase in thrifty gene caused by the famine

How does increased crunchiness of food affect enjoyment of food? (Lec)

Amplified frequency of crunchiness caused greater satisfaction of chip and was perceived as more crunchy and fresh

How does the size of a container affect the amount of food you eat? (Lec)

A larger container causes you to eat more food, even if the food is perceived to be disgusting

What trend is there in terms of the underweight vs overweight population? (Lec)

First time in history where there are way more overweight people than underweight people, continually increasing