Chemical Special Senses Smell
• Humans can perceive over 100,000 odorants
• We can distinguish between a few thousand of them
• Only 20% of them are perceived as pleasant
• Important for sensing danger (e.g. Spoiled meat, smoke), as well as making nutritious food pleasant and palatable
• To warm (or cool) and to moisturise the air we breathe
• To sample a small proportion of the inhaled air by passing it through the olfactory epithelium
• Your smell receptors are located in the olfactory epithelium, a thin sheet of cells deep inside the nasal cavity
• Only a small proportion of breathed air reaches this area
• Human olfactory epithelium = 10cm2
• Dog olfactory epithelium = 170cm2
• In addition, dogs have more receptors per cm2
• Olfactory receptor cells carrying cilia embedded in mucus, are found in the olfactory epithelium
• The other side of the receptor cells face the olfactory bulb, a protruding part of the cerebral cortex
• Unlike almost all other neurones in the body, olfactory receptors are continuously dividing (lifetime ~2 months)
• Each new neurone grows an axon to the olfactory bulb and forms the proper synaptic connections
Integration of Physiological Systems Page 1
• Humans can perceive over 100,000 odorants
• We can distinguish between a few thousand of them
• Only 20% of them are perceived as pleasant
• Important for sensing danger (e.g. Spoiled meat, smoke), as well as making nutritious food pleasant and palatable
• To warm (or cool) and to moisturise the air we breathe
• To sample a small proportion of the inhaled air by passing it through the olfactory epithelium
• Your smell receptors are located in the olfactory epithelium, a thin sheet of cells deep inside the nasal cavity
• Only a small proportion of breathed air reaches this area
• Human olfactory epithelium = 10cm2
• Dog olfactory epithelium = 170cm2
• In addition, dogs have more receptors per cm2
• Olfactory receptor cells carrying cilia embedded in mucus, are found in the olfactory epithelium
• The other side of the receptor cells face the olfactory bulb, a protruding part of the cerebral cortex
• Unlike almost all other neurones in the body, olfactory receptors are continuously dividing (lifetime ~2 months)
• Each new neurone grows an axon to the olfactory bulb and forms the proper synaptic connections
Integration of Physiological Systems Page 1
