Hunger and the Chemical Senses

Main reason for feeling hungry is

low blood glucose levels

glucose is important for

keeping body functions operational and is the primary source of energy for the brain

glucose is stored as

glycogen - can be released between meals

• mostly stored in the muscles and liver

glucose is released by the

liver to replenish blood glucose levels

pancreas secretes

insulin to promote the uptake of glucose body cells for immediate use

• also for excess glucose to be stored as glycogen

Neuropeptide Y (NPY)

high levels in hypothalamus is responsible for food seeking behaviours (like heading to the kitchen)

• increases carbs consumption

Brain receives Satiety signals from

• stretch receptors in the stomach via vagus n. (full literally)

• GI tract’s secretion of digestive hormones

• liver when high glucose and high glycogen storage

small intestine produces cholecystokinin (CCK) because

it is responsible for feelings of satiety

• brain receptors sense CCK = signal to stop eating

• short term satiety

Why do we store long term energy as fats?

• fat = twice the energy density that carbs

• fat = found in all parts of the body

adipose tissue secretes a hormone called

leptin - long term energy balance + correlates with fat mass

• reduced appetite = decreases food consumption

leptin production is controlled by the

OB gene - don’t have it in mice = obese mice cuz leptin production stops

leptin resistance

beyond certain level, effect of leptin on appetite is reduced

leptin indicates

low energy stores rather than inhibiting appetite

leptin acts to inhibit

NYP in the hypothalamus

endogenous opioids

naturally occurring chemical substances that have morphine-like analgesic actions in the body

• contributes to palatablility and reward driven feeding

cultural influences shape

taste response

why do I hate coffee but my parents love it??

might have to do with the number of taste buds

• highly sensitive tasters have more taste buds than the average person = sensitivity to more tastes

how does the brain process taste?

• taste receptor cells (on taste buds) detect and respond to food molecules and have some proportion to all 5 taste receptors

• afferent neurons send signals to the brain for processing = taste

taste receptor sends the signal to the

gustatory nerve and then to medulla (of the brain stem - has unconcious perception of taste so = gagging etc)

• most travel from the medulla to thalamus (relay for sensory info) then to many higher brain regions

gustatory cortex of brain

center for taste with specific neurons for each of the 5 tastes

• also connects to many other brain areas with other info = taste

primary somatosensory cortex and gustatory cortex is responsible for

taste and texture of food

orbital cortex and gustatory cortex is responsible for

taste and smell of food = flavour

• happens at nasopharynx at the back of the throat

taste signals go from thalamus to

hypothalamus to amygdala responsible for feeding behaviour = feeding and satiety (CCK)

spice contains

the chemical capsaicin which activates heat receptors in the mouth

smell is directly linked to the

cortex without being relayed to the thalamus first

how is smell processed?

1. chemical molec. enter dissolve in the mucus of nose = interacts with the olfactory cilia

2. olfactory receptor cells are activated and send electric signals

3. signals are relayed in the glomeruli

4. glomeruli send action potentials to higher regions in the brain

   • goes into olfactory pathway and limbic system

each smell activates a

unique pattern of firing across many receptors

output from the glomeruli are sent to

different parts of the brain - most goes to hypothalamus to limbic system = emotions

• also goes to primary olfactory cortex in temporal lobe + orbital cortex in frontal lobe