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. **17-3 Internal Eye Structures Contribute to Vision, while Accessory Eye Structures Provide Protection.** \*\*\* We rely more on vision than any other special sense. \*\*\* **Accessory Structures of the Eye** Accessory structures of the eye provide protection, lubrication, and support and include... - Eyelids - Superficial epithelium of the eye - Lacrimal apparatus **The Eyelids** **[Eyelids (palpebrae):]** continuation of skin. - Blinking keeps surface of eye lubricated and clean. - **[Palpebral fissure:]** gap that separates upper and lower eyelids. Eyelids are connected at... - Medial angle, also called, *medial canthus*. - Lateral angle, also called, *lateral canthus*. **[Eyelashes:]** robust hairs. - Help prevent foreign matter from reaching eye. **[Tarsal glands:]** secrete lipid-rich product that helps keep eyelids from sticking together. **[Lacrimal caruncle:]** mass of soft tissue at medial angle of eye. - Contains glands that produce thick secretions. **The Superficial Epithelium of the Eye** **[Conjunctiva:]** mucous membrane covered by an epithelium. **[Conjunctivitis (pinkeye):]** inflammation of conjunctiva. - **[Palpebral conjunctiva:]** covers inner surface of eye. - **[Bulbar conjunctiva:]** covers anterior surface if eye, extends to edges of cornea. **[Cornea:]** transparent part of fibrous outer layer that extends from the bulbar conjunctiva. **The Lacrimal Apparatus** **[Lacrimal apparatus:]** produces, distributes, and removes tears. **[Lacrimal gland:]** tear gland. - Produces tears that cover conjunctiva. - Secretions contain **[lysozyme:]** antibacterial enzyme. **[Fornix:]** pocket where palpebral conjunctiva joins bulbar conjunctiva. - Receives 10-12 ducts from lacrimal gland. **Tears** - Collect in lacrimal lake at medial angle of eye and pass through... - Lacrimal puncta (pores), - Lacrimal canaliculi (canals), - Lacrimal sac, - Nasolacrimal duct, - Nasal cavity. **Anatomy of the Eyeball** Layers of the wall of the eyeball \*\*\* layers are also called tunics. \*\*\* - Outer fibrous layer. - Intermediate vascular layer (uvea). - Deep inner layer (retina). **[Orbital fat:]** cushions and insulates each eye. **[Eyeball ]** - Hollow. - Filled with fluid. - Two interior cavities... - Small **[anterior cavity]** - **[Aqueous humor ]** - Large **[posterior cavity]** - **[Vitreous body ]** **The Fibrous Layer** The fibrous layer is the outermost layer of the eyeball. - **[Sclera:]** white of the eye. - **[Cornea:]** transparent portion. - **[Corneoscleral junction (corneal limbus):]** border between cornea and sclera. **The Vascular Layer** The uvea is the vascular layer of the eyeball. - **[Iris:]** colored part of the eye, contains blood vessels, melanocytes, and two layers of smooth muscle called pupillary muscles. - **[Pupillary muscles:]** change diameter of pupil. - **[Pupil:]** central opening of iris. - **[Ciliary body:]** attaches to iris and extends posteriorly to ora serrata. - Contains ciliary muscle and ciliary processes. - **[Ora serrata:]** serrated anterior edge of neural layer of retina. - **[Ciliary zonule (suspensory ligament):]** attaches lens to ciliary processes. - **[Choroid:]** vascular layer that separates fibrous and inner layers posterior to ora serrata. - Capillaries deliver oxygen and nutrients to retina. **Vascular Layer Functions** - Provides route for blood vessels and lymphatics that supply tissues of eye. - Regulates amount of light entering eye. - Secretes and reabsorbs aqueous humor that circulates within chamber of eye. - Controls shape of lens, which is essential for focusing. **The Inner Layer** Inner layer (retina) consists of a thin layer called the pigmented layer and a thicker covering called the neural layer. **[Pigmented layer:]** absorbs light that passes through neural layer. **[Neural layer:]** contains supporting cells and neurons - Outermost part contains **[photoreceptors]**. - Rods and cones. **Photoreceptors** - **[Rods]** (black/white/gray) - Do not discriminate colors. - Highly sensitive to light. - **[Cones]** (colors) - Provide color vision. - Densely clustered in **[macula]**. - Especially at **[fovea centralis (fovea)]**. - At center of macula, - Site of sharpest color vision. - Visual axis is the line from an object to the fovea. - **[Bipolar cells:]** synapse with rods and cones. - **[Ganglion cells:]** synapse with bipolar cells. **The Neural Layer: The Optic Disc** **[Optic disc:]** origin of optic nerve. - Circular region just medial to fovea. - No photoreceptors (blind spot). **The Chambers of the Eye** Ciliary body and lens divide interior of eye into... - **[Large posterior cavity ]** - **[Small anterior cavity ]** - Divided by iris into anterior and posterior chambers. **[Aqueous humor:]** fluid that circulates within anterior cavity. - Also diffuses through posterior cavity. - Enters scleral venous sinus (canal of Schlemm) at corneoscleral junction. - Reenters circulation at veins in sclera. - **[Intra-ocular pressure:]** fluid pressure in aqueous humor, helps retain eye shape. - **[Glaucoma:]** elevated intra-ocular pressure. **[Vitreous body:]** gelatinous mass in posterior cavity. - Helps stabilize shape of eye. - **[Vitreous humor:]** fluid portion of vitreous body. **Lens** **[Lens:]** held in place by ciliary zonule, also called, *suspensory ligaments*. - **[Cataracts:]** loss of transparency or cloudiness in lens. - **[Senile cataracts:]** most common form; natural consequence of aging. **[Lens fibers:]** enucleate cells in interior of lens. - Filled with **[crystallins]**, which provide clarity and focusing power.