5. Structure & Functions of Nose

5.1 Structure of Nose

NOTE– Structure of Nose discussed in Respiratory System.

5.2 Functions of Nose

Olfactory Receptors

• Smell (olfactory) receptors and taste receptors are chemoreceptors, which means that chemicals dissolved in liquids stimulate them. Smell and taste function closely together and aid in food selection because we usually smell food at the same time we taste it.

Olfactory Organs

• The olfactory organs, which contain the olfactory receptors, are yellowish-brown masses of epithelium about the size of postage stamps that cover the upper parts of the nasal cavity, the superior nasal conchae, and a portion of the nasal septum.
• Olfactory receptor cells are bipolar neurons surrounded by columnar epithelial cells.
• When stimulated by vapor molecules, olfactory receptors generate impulses carried by the olfactory nerves (1st cranial) through the ethmoid bone to the olfactory bulbs.

Olfactory Nerve Pathways

• Stimulated olfactory receptor cells send nerve impulses along their axons. These fibers (1st cranial nerves) synapse with neurons located in enlargements called olfactory bulbs.
• Within the olfactory bulbs, the impulses are analyzed, and as a result, additional impulses travel along the olfactory tracts to the limbic system.
• The major interpreting areas for these impulses in the olfactory cortex lie within the temporal lobes and at the bases of the frontal lobes, anterior to the hypothalamus.

Olfactory Stimulation

• When odorant molecules bind to olfactory receptor proteins in olfactory receptor cell membranes, a biochemical pathway is activated that culminates in an infl ux of sodium ions, which may trigger an action potential if the depolarization reaches threshold. The action potentials from this and other olfactory receptor cells travel to the olfactory bulbs in the brain, where the sensation of smell arises.