7.7

• Olfaction (smell) and gustation (taste) are referred to as the chemical senses because their function is to monitor the chemical content of the environment.
• Smell is the response of the olfactory system to airborne chemicals that are drawn by inhalation over receptors in the nasal passages.
• Taste is the response of the gustatory system to chemicals in solution in the oral cavity.
• Molecules of food excite both smell and taste receptors and produce an integrated sensory impression.

  Flavor
• In humans, the main adaptive role of the chemical senses is the evaluation of potential foods
• In many other species, the chemical senses also play a major role in regulating social interactions
• Chemicals that influence the physiology and behavior of conspecifics.

  Pheromones
• The upper part of the nose embedded in a layer of mucus-covered tissue where the olfactory receptor cells are located.

  olfactory mucosa
• True or False, in mammals, each olfactory receptor cell contains two types of receptor protein molecule.

  False, only one receptor protein
• The axons of olfactory receptors terminate in discrete clusters of neurons that lie near the surface of the olfactory bulbs—these clusters are called the olfactory glomeruli.
• The poorly understood topographic organization of the olfactory bulbs has been termed a chemotopic map.
• True or False, New olfactory receptor cells are created throughout each individual’s life to replace those that have deteriorated.

  True
• Each olfactory bulb projects axons to several structures of the medial temporal lobes, including the amygdala and the piriform cortex.
• An area of medial temporal cortex adjacent to the amygdala that is considered to be primary olfactory cortex, but this designation is somewhat arbitrary.

  Piriform Cortex
• The only sensory system whose major sensory pathway reaches the cerebral cortex without first passing through the thalamus.

  Olfactory System
• Two major olfactory pathways leave the amygdala-piriform area:

  1. Limbic System
  2. medial dorsal nuclei
• The limbic pathway is thought to mediate the emotional response to odors.
• The medial dorsal nuclei of the thalamus to the orbitofrontal cortex mediate the conscious perception of odors.
• The area of cortex on the inferior surface of the frontal lobes next to the orbits.

  Orbitofrontal cortex
• Taste receptor cells are found on the tongue and also throughout the gastrointestinal tract.