Chapter 14

The Chemical Senses

• Olfaction - many kinds of information• Taste (gustation) - food information• Trigeminal - noxious information

Olfactory System

• Anatomy• Olfactory epithelium--> olfactory bulb-->

olfatory tract --> pyriform cortex and other forebrain structures, amygdala and hypothalamus.

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The map of olfactory processing in the brain

• Not really understood

What can we smell?

• Airborne odours• Concentration:

– e.g.(pizza odour) IBMP, 2 nM– similar chemical structures are perceived

differently, e.g. spearmint and caraway seeds

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What can we smell?

• Changes with age– E.g. Children smell crayons– Adults, oregano is pleasant

Concentration differences

• Floral in low dose is pleasant– Is putrid in high dose

mixtures

• Most odours are composed of very many chemicals.– E.g. stawberry odor has about 60

compounds

Old age

• Loose ability to correctly identify an odor.

• The corresponding region of the brain is not active too.

Physiological and behavioural responses to odours.

• Visceral responses: Smell food--> salivation and gastric motility– Noxious smell-->gag

Physiological and behavioural responses to odours.

• Reproductive and endocrine functions– Women housed together synchronize

menstral cycles– Smelling gauze pads from underarms of

women also synchronizes menstral cycles.

Physiological and behavioural responses to odours.

• Infants recognize mothers by scent• Mothers can recognize the scent her

baby.

Pheromones

Species specific odorants.

Some pheromones stimulate the vomeronasal organ

VNO--> accessory olfactory bulb-->hypothalamus.

(Found in 8% of human adults), VNO receptors are pseudogenes in humans.

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Olfactory receptor (sensory) neuron

• In the olfactory epithelium• Have cilia projecting into the nasal

cavity mucus• These cells become damaged, and

turnover.

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Transduction

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Two olfactory subsystems

• Main • Vomeronasal