Chapter 17: The Special Senses PDF

**[Chapter 17: The Special Senses ]** **An Introduction to the Special Senses** Special Senses - Olfaction (smell) - Gustation (taste) - Vision - Equilibrium (balance) - Hearing **17-1 Olfaction, the Sense of Smell, Involves Olfactory Receptors Responding to Airborne Chemical Stimu...

**[Chapter 17: The Special Senses ]** **An Introduction to the Special Senses** Special Senses - Olfaction (smell) - Gustation (taste) - Vision - Equilibrium (balance) - Hearing **17-1 Olfaction, the Sense of Smell, Involves Olfactory Receptors Responding to Airborne Chemical Stimuli.** **[Olfaction:]** sense of smell. **Anatomy of the Olfactory Organs** **[Olfactory organs:]** located in nasal cavity on either side or nasal septum. - Made up of two layers... - Olfactory epithelium. - Lamina propria. Olfactory epithelium contains... - **[Olfactory sensory neurons:]** highly modified nerve cells that detect dissolved chemicals as they interact with odorant-binding proteins. - Supporting cells. - Basal epithelial cells (stem cells). Lamina propria contains... - Areolar tissue, blood vessels, and nerves. - **[Olfactory glands:]** secretions form mucus. **Olfactory Receptors and the Physiology of Olfaction** Olfactory reception begins with binding of odorant to G-protein-coupled receptor and creates **[generator potential]** (depolarization). **Olfactory Pathways** - Afferent fibers leave olfactory epithelium... - Collect into 20 or more bundles. - Penetrate cribriform plate of ethmoid. - Reach olfactory bulbs of cerebrum where first synapse occurs. - Axons leaving olfactory bulb... - Travel along olfactory tract to **[olfactory cortex] (in the temporal lobe)**, hypothalamus, and limbic system. - Olfactory information is the only type of sensory information to reach cerebral cortex directly. - All other sensations are relayed from thalamus. **Olfactory Discrimination** We can distinguish thousands of chemical stimuli. - Dogs have 72 times more olfactory receptor surface area than humans do. - Thus, their sense of smell is more than 10,000 times better than ours. - Olfactory receptors are replaced frequently, BUT total number of neurons declines with age. **17-2 Gustation, the Sense of Taste, Involves Gustatory Receptors Responding to Dissolved Chemical Stimuli.** **[Gustation (taste):]** provides information about food and liquids consumed. **Anatomy of Papillae and Taste Buds** Gustatory epithelial cells (taste receptors) are found in taste buds. - Distributed on superior surface of tongue and portions of pharynx and larynx. - Associated with epithelial projections (lingual papillae) on surface of tongue. **Types of Lingual Papillae** - **[Filiform papillae:]** do not contain taste buds. *Looks like a flame.* - **[Fungiform papillae:]** contains about 5 taste buds. *Looks like a mushroom.* - **[Vallate (Circumvallate) papillae:]** contain as many as 100 taste buds each. - **[Foliate papillae:]** have taste buds. **[Taste buds:]** contain basal epithelial cells (stem cells). **Gustatory Receptors** - **[Gustatory epithelial cells ]** - Extend microvilli through **[taste pore]**. - Replaced about every 10 days. - Innervated by cranial nerves that synapse in solitary nucleus of medulla oblongata, - Travels to thalamus and gustatory complex of insula. **Gustatory Discrimination and Physiology of Gustation** **There are four primary taste sensations.** - **[Sweet ]** - **[Salty ]** - **[Sour ]** - **[Bitter ]** There are two additional taste sensations. - **[Umami:]** pleasant, savory taste imparted by glutamate. - Characteristic of broths. - **[Water:]** detected by water receptors in pharynx.