Chemical SensesSmell

1
Chemical Senses-Smell

• Macrosmatic (Dog) vs
• Dogs are 300 to 10K more sensitive (e.g. bomb,
  cadaver, fish, drug detecting dogs)
• Microsmatic (Human)
• Sensitivity varies w the number of receptors not
  sensitivity of individual receptors (10 million
  in humans vs 1 billion in dogs)
• Anosmia

2
Chemical Senses-Smell

• Receptors

3
Chemical Senses-Smell

• Receptors

4
Chemical Senses-Smell

• Olfactory Receptors (OR) are part of the
  membranes of cilia of the ORNs
• Consist of proteins that cross through the
  membrane
• There are approx 1,000 different ORs that respond
  to the same class of molecules
• The ORs on a particular ORN are the same
• 10K of each type of ORN 10 Million ORNs

5
Chemical Senses-Smell

• Olfactory Receptors (OR)
• Response of the ORs in a section of the Olfactory
  Mucosa. Two receptors respond to both substances

6
Chemical SensesSmell

• Response of Frog receptors to different
  substances
• There is a pattern of receptor responses to each
  substance

7

• Olfactory Mucosa has four zones. ORNs from each
  zone communicate to a zone on the Olfactory Bulb.
  Each Glomerulus receives 5-10K ORNs. Each
  Glomerulus receives one type of ORN.
• The bulb becomes a map of the types of substances
  detected by smell.

8
Chemical Senses-Smell

• Response of Olfactory Bulb to different
  substances
• There is a position associated with each substance

9
Chemical Senses-Smell

• CNS Pathways

10
Chemical Senses-Smell

• Responses of Two Neurons in the Orbital Frontal
  Cortex to different substances

11
Chemical Senses-Smell

• Smell Naming and Memory
• The perception of a particular smell is
  influenced by memory associations for the name of
  the smell.
• If a subject is given an ambiguous smell
  stimulus and told it is smell X, then the subject
  will perceive the smell as X.

12
Chemical Senses-Smell

• Identifying others by smell
• Humans can generally identify males vs females by
  smell alone. This works for body and breath odor.
• Women who synchronize the menstrual cycle likely
  do this using smell.