Hunger and the Chemical Senses

Uptake of glucose function

• Some can be used immediately for energy

• Some stored as glycogen for later

• Excess stored as adipose

Neuropeptide Y Function

Drives high levels of activity in the hypothalamus which are associated with increased appetite and food seeking behaviours

Stretch receptors in stomach function

Stretch receptors in stomach are activated as it fills with food or water which sends signals through the vagus nerve that connects the gut and brainstem

CCK

Short-term satiety hormone from small intestine

how is weight regulated long term?

Long-term energy storage comes from adipose tissue because it is 9 cals vs glycogen that is 4 cals

Leptin

Hormone from adipose tissue that reduces appetite and involved in long-term energy balance

OB gene

Controls leptin production

Leptin resistance

Increasing leptin will reduce effectiveness of leptin in suppressing appetite because the individual will become leptin resistant

Evolutionary Purpose of Leptin

Likely that leptin’s primary function was to serve as an indicator of low energy stores back in the day, rather than a signal to stop eating

Leptin and NPY interaction

• Leptin inhibits actions of NPY leading to decreased appetite and energy consumption

• When glycogen reserves get low and NPY levels increase to signal a need for food, leptin can be secreted from adipose to inhibit it

High leptin levels

Not always associated with decreased food intake

NPY Promotes?

behaviours that lead to increased carbohydrate consumption

Endogenous opioids

• Naturally occurring chemical substances that have morphine like analgesic actions in the body

• Contributes to palatability (pleasure of taste) and reward driven feeding

Naloxone

Reduces intake of sweet and salty substances

Taste

Was an indication of nutritional quality of food

Sweet, salty, savoury (umami) associated with

Safe, nutritious foods

Bitter and sour associated with

Warn of potentially harmful or spoiled food

Taste buds receptor cells

Contain 50–150 receptor cells which detect and respond to food molecules

Taste bud location

2/3 on the tongue, also soft palate and throat

Five basic tastes

Sweet, salty, bitter, sour, umami

Salty

Signals electrolytes

Umami

Detects amino acids like glutamate and aspartate

Taste pathway

• taste receptor → gustatory nerve → medulla in the brainstem

• Most taste information then travels to the thalamus and sent to either the gustatory cortex to hypothalamus

what information is sent to the brainstem

reflexes, gag reflex

Gustatory cortex

• Main processing center for taste

• Has specific neurons that respond to each of the five basic tastes

• Connects to primary somatosensory cortex and orbital cortex

Primary somatosensory cortex role

combine taste with feel and texture

Orbital cortex role

combines taste and smell to enhance flavour

Hypothalamus and amygdala

• Control emotional and hormonal aspects of feeding

• involved in cessation and feeding, along with CCK activity

Retronasal smell

As you chew or swallow food/drinks, odourants (smell) travel from the back of the throat up to the receptors in the nasal cavity that process smell and allows for a more sophisticated ability to sense flavour

Spice

Not a taste, results from the chemical capsaicin binding to heat and pain receptors in the mouth which cause the receptors to fire APs

how many smells can we distinguish

up to 10,000 odors

Smell pathway

Bypasses thalamus and goes directly to cortex, could be because smell is important to alert us

Smell Processing in the Nose

• Odourants enter nasal cavity and dissolve in the mucus of the nose

• The molecules interact with olfactory cilia that cover the receptor cell surface

• About 10 to 20 cilia for each receptor cell

how do odourant molecules get processed into nerve signals?

1. Odourant molecules bind to receptors

2. Receptors fire action potentials

3. Action potentials travel down the receptors’ axons to olfactory bulb

4. Receptors’ axons synapse with glomeruli (dendrites

5. Glomeruli send action potentials to higher regions of the brain

Smell Output from Glomeruli to the Brain

• Most is sent to hypothalamus and limbic system which deal with basic drives and emotions

• Some goes to the primary olfactory cortex in the temporal lobe

• Some goes to orbital cortex in the frontal lobe

Thrifty gene

Promotes efficient fat storage, contributing to obesity today