Chapter 8Special Senses –

Chemoreceptors: Taste & Smell

Chemical Senses – Taste & SmellChemical Senses – Taste & Smell

Both senses use chemoreceptors

- Stimulated by chemicals in solution

- Taste - 5 types of receptors

- Smell - large range of chemicals

Both senses complement each other and respond to many of the same stimuli

SmellSmell

Olfaction – The Sense of SmellOlfaction – The Sense of Smell

Olfactory receptors are in roof of the nasal cavity

- Neurons with long cilia

- Chemicals must be dissolved in mucus for detection

Impulses are transmitted via the olfactory nerve

Interpretation of smells is made in the cortex

Olfactory EpitheliumOlfactory Epithelium

Taste

The Tongue and TasteThe Tongue and Taste

The tongue is covered with projections called papillae

- Filiform – pointy with no taste buds

- Fungifiorm – rounded with taste buds

- Circumvallate – large with taste buds

Taste buds are found on the sides of papillae

The Sense of TasteThe Sense of Taste

Taste buds house the receptor organs

Location of taste buds

- Most are on tongue

- Soft palate

- Cheeks

Structure of Taste BudsStructure of Taste Buds Gustatory cells are the receptors

- Hairs stimulated by chemicals dissolved in saliva

1 taste bud = cluster of 100 specialized cells few exposed at a time.

Taste bud lifespan is about 10 days

Cranial Taste NervesCranial Taste NervesImpulses carried to

the gustatory complex by several cranial nerves because taste buds are found in different areas

Facial nerve

Glossopharyngeal nerve

Vagus nerve

Taste SensationsTaste Sensations1. Sweet receptors (-OH groups)

Sugars Saccharine Some amino acids

2. Sour receptors Acids

3. Bitter receptors Alkaloids

4. Salty receptors Metal ions

5. Umami receptors (meaty/savory) Glutamate

Developmental AspectsDevelopmental Aspects Formed early in

embryonic development

All special senses are functional at birth, but vision isn’t fully developed.

- Eyes are outgrowths of brain, born ½ size; grow mostly 1st yr & until puberty

- Baby’s focal length is ~9”.

- Reaches 20’ by age 3.