Overview of Chemical Senses: Olfaction and Gustation

General Senses

Somatic sensations scattered throughout the body, including tactile, thermal, pain, proprioceptive, and visceral sensations.

Special Senses

Smell, taste, vision, hearing, and equilibrium, which are concentrated in specific locations in the head and have anatomically distinct structures.

Chemical Senses

Interaction of molecules with receptor cells, specifically olfaction (smell) and gustation (taste), which both project to the cerebral cortex and limbic system.

Olfaction

The sense of smell.

Gustation

The sense of taste.

Odor

A general smell sensation of a particular quality.

Odorant

Any specific aromatic chemical that must be a molecule that is volatile, small, and hydrophobic.

Total Anosmia

Inability to smell all odorants.

Partial Anosmia

Inability to smell certain odorants.

Specific Anosmia

Lack of ability to smell one or a few odorants.

Hyperosmia

Abnormally acute smell function often interpreted as hypersensitivity to odors.

Dysosmia

Distorted or perverted smell perception.

Parosmia/Cacosmia

Change in the quality of an olfactory cue.

Phantosmia

Odor sensations in the absence of an olfactory stimulus.

Olfactory Agnosia

Inability to recognize odor sensations despite olfactory process, language, and intellectual function, often seen in certain stroke patients.

Presbyosmia

Smell loss due to aging.

Olfactory Epithelium

1 square inch of membrane holding 10-100 million receptors, covering the superior nasal cavity and cribriform plate.

Olfactory Nerves

Nerves that leave the nasal cavity through small holes in the cribriform plate of the ethmoid bone.

Olfactory Bulbs

Receive 15 to 20 olfactory nerve fibers that relay information about incoming odors from the olfactory receptor cells.

Olfactory Tract

Relay incoming signals from the olfactory bulb to the cerebrum.

Adaptation

Decreasing sensitivity to odors, which occurs rapidly.

Olfactory Pathway

Impulse generated in olfactory receptor cells travels through olfactory nerve fibers to the olfactory bulb and tract, reaching the primary olfactory cortex, limbic system, and hypothalamus.

Pheromones

Chemicals released by one member of a species and received by another member, resulting in a specific action or developmental process.

Taste Buds

Structures found on the tongue, soft palate, oropharynx, epiglottis, and inner cheeks that contain gustatory receptor cells.

Primary Tastes

Five primary tastes: sour, sweet, bitter, salty, and umami (meaty/savory).

Lingual Papillae

Elevations on the tongue that increase surface area and provide a rough texture.

Vallate Papillae

8-12 large papillae arranged in a 'V' near the base of the tongue, each containing 100-300 taste buds.

Fungiform Papillae

Knoblike projections of the tongue scattered over the entire tongue, each containing about 5 taste buds.

Foliate Papillae

Small trenches on the lateral margins of the tongue that mostly degenerate in early childhood.

Filiform Papillae

Threadlike elevations covering most of the tongue that serve as tactile receptors but do not contain taste buds.

Gustatory Transduction

The process by which dissolved substances contact gustatory hairs, resulting in receptor potential and neurotransmitter release.

Gustatory Pathway

Pathway that includes first-order gustatory fibers in cranial nerves, signals traveling to the gustatory nucleus in the medulla oblongata, and extending to the primary gustatory area on the parietal lobe of the cerebral cortex.