Chapter 17 – Special Senses (Smell, Taste, Vision, Hearing, Equilibrium)

What type of senses are smell and taste?

Chemical senses.

Where is the olfactory epithelium located?

It lines the superior part of the nasal cavity, covering the inferior surface of the cribriform plate and superior nasal concha.

Approximately how many olfactory receptor cells does the human nose contain?

10–100 million.

Name the three cell types in the olfactory epithelium.

Olfactory receptor cells, supporting cells, and basal cells.

What is the function of basal cells in the olfactory epithelium?

They undergo mitosis to replace olfactory receptor cells.

What do Bowman’s (olfactory) glands secrete and why?

Mucus, to dissolve odor molecules for transduction.

Through which structure do olfactory nerve axons pass to reach the olfactory bulb?

Cribriform plate of the ethmoid bone.

Which brain lobe contains the primary olfactory area?

Temporal lobe.

Which second messenger is involved in olfactory transduction?

Cyclic AMP (cAMP).

Why is methyl mercaptan added to natural gas?

Because olfaction has a low threshold; tiny amounts of methyl mercaptan provide a warning odor for gas leaks.

How quickly do olfactory receptors adapt by about 50 % after stimulation?

Within the first second.

List the five primary tastes.

Sour, sweet, bitter, salty, and umami.

Roughly how many taste buds does a young adult have?

About 10 000.

Name the three epithelial cell types in a taste bud.

Supporting cells, gustatory receptor cells, and basal cells.

Which papillae contain the greatest number of taste buds per papilla?

Vallate (circumvallate) papillae—about 12 papillae with 100–300 taste buds each.

Which tongue papillae provide friction but contain no taste buds?

Filiform papillae.

What are tastants?

Chemicals that stimulate gustatory receptor cells.

How do salty tastants depolarize gustatory cells?

Na⁺ ions enter through Na⁺ channels, causing depolarization and neurotransmitter release.

Which cranial nerves carry taste information?

Facial (VII), Glossopharyngeal (IX), and Vagus (X).

Where is the primary gustatory area in the brain?

In the insula of the cerebral cortex (just inferior to the post-central gyrus).

Which taste modality has the lowest threshold?

Bitter (many poisons are bitter).

What wavelengths of light form visible light?

Approximately 400–700 nm.

List the accessory structures of the eye.

Eyelids, eyelashes, eyebrows, lacrimal apparatus, and extrinsic eye muscles.

Trace the pathway