The Olfactory System

The Olfactory System, or sense of smell, which senses and processes odors, is one of the oldest and most vital parts of the brain. For most animals, it is the primary mode of communication and influences many important functions, including reproduction and taste.The nose contains specialized sensory nerve cells, or neurons, with hairlike fibers called clilia on one end. Each neuron sends a nerve fiber called an axon to the olfactory bulb, a brain structure just above the nose.Olfactory information travels not only to the limbic system — primitive brain structures that govern emotions, behavior, and memory storage — but also to the brain’s cortex, or outer layer, where conscious thought occurs. In addition, it combines with taste information in the brain to create the sensation of flavor. Learning more about these links will help explain how odors affect our thoughts, emotions and behavior.


Odor molecules entering the nose are thought to be recognized by receptors found in cilia of olfactory neurons. Neurons with specific receptors are arranged randomly within zones in the olfactory lining of the nasal cavity. Signals from neurons with the same receptors converge on structures called glomeruli in the olfactory bulb. The pattern of activity in these glomeruli creates a pattern or code that the brain may interpret as different odors. The information is carried by nerve fibers to many brain regions, where it affects thoughts, emotions, and behavior.

SIGNS OF OLFACTORY DYSFUNCTION (smells):

1. HYPERSENSITIVITY TO SMELLS (over-responsive):

  • reacts negatively to, or dislikes smells which do not usually bother, or get noticed, by other people
  • tells other people (or talks about) how bad or funny they smell
  • refuses to eat certain foods because of their smell
  • offended and/or nauseated by bathroom odors or personal hygiene smells
  • bothered/irritated by smell of perfume or cologne
  • bothered by household or cooking smells
  • may refuse to play at someone’s house because of the way it smells
  • decides whether he/she likes someone or some place by the way it smells

2. HYPOSENSITIVITY TO SMELLS (under-responsive):

  • has difficulty discriminating unpleasant odors
  • may drink or eat things that are poisonous because they do not notice the noxious smell
  • unable to identify smells from scratch ‘n sniff stickers
  • does not notice odors that others usually complain about
  • fails to notice or ignores unpleasant odors
  • makes excessive use of smelling when introduced to objects, people, or places
  • uses smell to interact with objects

The Seven Senses

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