Chemical Senses: Taste and Smell

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• Receptors for taste and smell are called chemoreceptors because they detect chemicals

• Taste and smell complement each other and respond to many of the same stimuli.

Chemoreceptors

The Sense of Smell

• Thousands of olfactory (smell) receptors are located in the roof of each nasal cavity

• Olfactory receptor cells are neurons with olfactory hairs 

  • Olfactory hairs are long cilia that are bathed in mucus.

• Olfaction is the act of smelling

• Hair cells are stimulated by chemicals dissolved in mucus

• Impulses are transmitted to the olfactory bulb  which then sends smell information to olfactory centers in the temporal lobe 

• Olfactory pathways are closely tied to the limbic system (emotional-visceral part of the brain) which is why some smells trigger memories and emotions

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Olfactory Bulb

Multiple Choice

Olfaction is

• the sense of taste
• the sense of touch
• the sense of smell
• the sense of hearing

The Sense of Taste

• Taste buds are the receptors for the sense of taste

• They are found throughout the oral cavity, but most are located on the tongue

• Usually found on projections called papillae

• Taste likes and dislikes serve a homeostatic function

• A particular nutrient the body needs may taste very appealing whereas spoiled food, which could damage the body, usually has an unpleasant taste

• The average adult has about 9,000-10,000 taste buds

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• Filiform: provide sense texture and temperature of food, no taste buds

• Fungiform: contain taste buds, larger & darker, mostly at tip and along the sides

• Circumvallate: large, located at the back of the tongue, contain taste buds in the side walls

3 Types of Papillae

Categorize

Options (6)

Provide texture

No taste buds

Found at the tip

large

Back of tongue

Larger and darker

Organize these options into the right categories pf papillae

Filiform

Circumvallate

Fungiform

• Gustation is sensory detection of food on the tongue; the sense of taste.

• Taste receptor cells are called gustatory cells

• Have long microvilli called gustatory hairs that protrude through a taste pore

• Impulses travel to the brain through various cranial nerves.

• Each taste bud contains approximately 50-75 Gustatory cells.

Gustatory Cells

Multiple Choice

Olfactory cells and Gustatory cells are both examples of

• visual cells
• Chemoreceptors

• auditory cells
• taste buds

5 Basic Taste Sensations

• Sweet receptors detect sugar 

• Sour -  acids 

• Bitter - alkaloids 

• Salty - metal ions 

• Umami  - amino acid glutamate which is responsible for “beef taste”

Developmental Aspects

• Eyes are not fully functional for several years (Vision is the only special sense that is not fully functional)

• Responses to sounds are mostly reflexive

• Babies have a highly developed sense of smell and more taste buds than adults

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​Special Senses at Birth

• Decreasing lens elasticity makes it difficult to focus on close objects

• Lacrimal glands become less active leading to dry eyes

• Lens loses clarity

​Effect of Aging on Eyesight

• Organ of Corti & other ear structures begin to deteriorate leading to hearing loss

• About half of people over age 80 cannot smell at all & taste is also diminished

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​Effect of Aging on Other Senses

Multiple Choice

This sense is not fully developed in Newborns

• hearing
• touch
• taste
• sight