Chapter 8 Special Senses – Chemoreceptors: Taste & Smell

Chemical 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

Smell

Olfaction – 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 Epithelium

Taste

The 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 Taste  Taste buds house the receptor organs  Location of taste buds -Most are on tongue -Soft palate -Cheeks

Structure 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 Nerves Impulses carried to the gustatory complex by several cranial nerves because taste buds are found in different areas  Facial nerve  Glossopharyngeal nerve  Vagus nerve

Taste Sensations 1. 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 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 1 st yr & until puberty -Baby’s focal length is ~9”. -Reaches 20’ by age 3.