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Module 1 The Nervous System

Lesson 1.1.4

1.1.4 page 4

Smell

Ah, the scent of pizza. Or maybe the scent of a fragrance as you approached that special person. It makes you want to get closer. But the friend that you’re with is sneezing a lot and his nose and eyes are running. Are your senses communicating perceptions that are quite different than those which your friend is perceiving? To learn more about smell and what it communicates, read page 426 of your textbook.

 

Smell, much like taste, detects chemicals in solution. Olfactory receptor cells are stimulated by chemicals only when in solution. A sensory nerve communicates this information to the frontal and temporal lobes of the brain. Cells in the olfactory epithelium produce a continuous secretion of mucous in which molecules of airborne chemicals dissolve. Mucous is continuously secreted to flush away old odour chemicals so that new odour chemicals may gain access to the receptors. Smells associated with dangers such as smoke, natural gas, or skunk musk trigger the sympathetic nervous system. The perception of unpleasant odours can trigger sneezing or a gag reflex. Your friend’s perceptions are very different from yours!

 

olfactory epithelium: a patch of tissue located in the upper part of the nasal cavity that contains mucous secreting cells and olfactory cells, or smell cells, that can detect different smells; a sense organ for smell

 

olfactory receptor cell: a neuron specialized to receive chemical stimuli and to initiate a nerve impulse

Self-Check

Complete the Smell Reception Handout below. Self-check and store your work in your course folder.

Smell Reception Handout
  1. Label the structures 1 to 14.

    Inquiry into Biology (Whitby, ON: McGraw-Hill Ryerson, 2007), 427, fig. 12.26. Reproduced by permission.

  1. What has to happen to airborne chemicals like those of a rose before they can be smelled?
  2. What is the function of structure 10?
  3. What is the purpose of the olfactory cilia on the olfactory cell (receptor cell)?
  4. Where is the nerve impulse initiated?
  5. Outline the specific sensory pathway involved in smelling a rose.
Check your work.
Self-Check Answers

Answers for Smell Reception Handout

  1. frontal lobe of cerebrum
  2. olfactory bulb on underside of cerebrum
  3. olfactory epithelium
  4. airborne chemicals from rose
  5. nasal cavity
  6. olfactory bulb enlarged
  7. sensory neuron
  8. bone
  9. sensory fibres
  10. olfactory gland
  11. olfactory (smell) cell
  12. cilia (hairs) on olfactory cell
  13. odour molecules dissolved in mucous
  14. olfactory epithelium
  1. Airborne chemicals have to be dissolved before they can fit into receptors on olfactory cells.
  2. The olfactory glands (structure 10) continually produce mucous to dissolve airborne chemicals and to wash away “old” odours.
  3. The cilia (hairs) increase the surface area so that more odour molecules may reach more receptors.
  4. The nerve impulse is initiated at the cilia on the olfactory cell and transmitted to the neurons in the olfactory bulb.
  5. The main steps of smell perception include the following:
  • Odour molecules are breathed into the nasal cavity.
  • Odour molecules dissolve in mucous produced by olfactory glands of the nasal epithelium.
  • The molecules in solution attach to receptors on the cilia (hairs) of olfactory cells.

    The sensory receptors or olfactory cells (specialized neurons) initiate nerve impulses which are sent via the sensory neuron to the olfactory bulb and then to the temporal lobe of the cerebrum where it is interpreted as a scent.