Psych 1XX3 - Hunger and the Chemical Senses

Satiety

signals lead you to stop consumption

Glucose

- preferred source of energy for the brain

- low levels stimulate hunger

Glycogen

mainly stored in liver, some in muscles

- broken down when glucose is low

NPY

- stimulates appetite, food consumption

- found in hypothalamus

- inhibited by Leptin

Liver

- sends signals to trigger satiety

Eg. dog stops eating if glucose is injected into a vein that connects directly to it

CCK

- produced by small intestine

- triggers short term satiety

- if injected with it, subjects feel full sooner

Eg. Rats increased meal frequency and decreased duration of meals when injected with CCK

Adipose Tissue

long term energy stores in animals

- endocrine organ

- 2x energy of glucose

- active component of regulatory physiology

Leptin

- found in adipose tissue

- low levels lead to increased foraging, inhibits appetite

- correlated with fat mass

- controlled by OB gene

- high levels inhibits NPY = decreased hunger

- humans become leptin resistant if given high levels

- plays role in addictive behaviour

Endogeneous Opioids

- naturally occurring chemical substances

- have morphine-like analgesic actions in the body

- reward-driven feeding

- (could be reason for overeating)

Naloxone

reduces intake of saccharin, sucrose and saline

Taste Preferences

- governed by older brain regions

- bitter/sour = not enjoyed (dangerous)

- sweet/salty/savoury = rich in energy (safe)

- evolutionary advantage = could distinguish these tastes

Picky Eaters Study

- result = infants with brain damage would still distinguish between good tasting and bad tasting

Cultural Influences

- taste preferences

- foods you enjoy are learned from experience

Chemical Senses

- depend on receptors that can interact with molecules of food particles

- taste and smell influence perception of flavour

Taste Buds

contains 50-150 taste detector cells

Taste Receptors

- 5 types

- all areas of tongue detect 5 basic tastes

- afferent neurons send signals to the brain

- fires action potential

Main Gustatory Nerve

- information sent to brainstem

- diverges into two pathways

Pathways to Taste

Medulla -> Thalamus -> Primary Somasensatory Cortex & Gustatory Cortex

-> Orbital Cortex

Brainstem -> Pons -> Hypothalamus -> Amygdala

Somasensatory Cortex

where feel and texture of food is processed and where on the tongue food is located

Gustatory Cortex

sets of neurons that respond to the 5 basic tastes

Orbital Cortex

near olfactory cortex (where smell is)

Flavour

Smell + Taste

Advantages of Smell

- direct route to the cortex without being first routed to the thalamus

- advantage of finding food and mates

Olfactory Receptor Cells

- receive information from 10-20 cilia in nose

- combine smell and taste to get flavour

Nasal Cavity

Olfactory Epithelium (where flavour happens)

food engineering

engineered to be resistable

- frequency crunch, taste that doesnt last too long

reducing frequency and volume of crunch

staler, less crunchy chip

OB Gene

leptin gene

- without it, subjects become extremely obese

explain the process after eating a meal

- high bood sugar levels leads to release of insulin

- insulin signals body to uptake glucose, store excess as glycogen and adipose

- glycogen converted to glucose as needed

- eat when stores are depleted

taste sensitivity

correlated with higher number of taste buds

pregnancy and taste

mom extra sensitive during first trimester, corresponds to when fetus is most sensitive to harmful substances

sweet

energy rich (fruits and sugar)

sour/bitter

harmful, spoiled, potentially poisonous

umami

savoury, amino acids glutamate and aspartate

salty

essential electrolytes

pathway 2

thought to be involved in other aspects of eating & feeding behaviour

- satiety, feeding cessation

why is smell a unique sense?

it skips the thalamus (direct link to cortex)

how does smell work?

- odorant molecules bind to smell receptors

- molecules interact with cilia

- AP triggered in olfactory receptor cell

- axon synapses in olfactory bulb of brain with glomuruli (thousands of OR cells per glomuruli)

glomuruli output

different areas of brain

- most to hypothalamus & limbic system that deal with basic drives and emotion

- primary OC (temp lobe)

- secondary OR (frontal lobe)

orbifrontal cortex

involved in addiction, impulsive if lacking

- processes food related pleasures

amygdala and eating

becomes active when it detects something important to organisms survival

- hungry subjects have active amygdalas