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Chapter 17 the Special Senses

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Chapter 17 The Special Senses An Introduction to the Special Senses Five Special Senses 1. Olfaction 2. Gustation 3. Vision 4. Equilibrium 5. Hearing 17-1 Smell (Olfaction) Olfactory Organs o Provide sense of smell o Located in nasal cavity on either side of nasal septum o Made up of two layers 1. Olfactory epithelium 2. Lamina propria 17-1 Smell (Olfaction) Layers of Olfactory Organs o Olfactory epithelium contains: . Olfactory receptors . Supporting cells . Basal (stem) cells 17-1 Smell (Olfaction) Layers of Olfactory Organs o Lamina propria contains: . Areolar tissue . Blood vessels . Nerves . Olfactory glands 17-1 Smell (Olfaction) Olfactory Glands o Secretions coat surfaces of olfactory organs Olfactory Receptors o Highly modified neurons © 2015 Pearson Education, Inc. o Olfactory reception . Involves detecting dissolved chemicals as they interact with odorant- binding proteins 17-1 Smell (Olfaction) Olfactory Pathways o Axons leaving olfactory epithelium . Collect into 20 or more bundles . Penetrate cribriform plate of ethmoid . Reach olfactory bulbs of cerebrum where first synapse occurs 17-1 Smell (Olfaction) Olfactory Pathways o Axons leaving olfactory bulb: . Travel along olfactory tract to reach olfactory cortex, hypothalamus, and portions of limbic system o Arriving information reaches information centers without first synapsing in thalamus 17-1 Smell (Olfaction) Olfactory Discrimination o Can distinguish thousands of chemical stimuli o CNS interprets smells by the pattern of receptor activity Olfactory Receptor Population o Considerable turnover o Number of olfactory receptors declines with age 17-2 Taste (Gustation) Gustation o Provides information about the foods and liquids consumed Taste Receptors (Gustatory Receptors) o Are distributed on tongue and portions of pharynx and larynx o Clustered into taste buds 17-2 Taste (Gustation) Taste Buds o Associated with epithelial projections (lingual papillae) on superior surface of tongue 17-2 Taste (Gustation) Four Types of Lingual Papillae © 2015 Pearson Education, Inc. 1. Filiform papillae . Provide friction . Do not contain taste buds 2. Fungiform papillae . Contain about five taste buds each 3. Vallate papillae . Contain 100 taste buds each 4. Foliate papillae . 17-2 Taste (Gustation) Taste Buds o Contain: . Basal cells . Gustatory receptor cells o Extend taste hairs through taste pore o Survive only 10 days before replacement . Monitored by cranial nerves that synapse within solitary nucleus of medulla oblongata o Then on to thalamus and primary sensory cortex 17-2 Taste (Gustation) Gustatory Discrimination o Four primary taste sensations 1. Sweet 2. Salty 3. Sour 4. Bitter 17-2 Taste (Gustation) Additional Human Taste Sensations o Umami . Characteristic of beef/chicken broths and Parmesan cheese . Receptors sensitive to amino acids, small peptides, and nucleotides o Water . Detected by water receptors in the pharynx 17-2 Taste (Gustation) Gustatory Discrimination o Dissolved chemicals contact taste hairs o Bind to receptor proteins of gustatory cell o Salt and sour receptors . Chemically gated ion channels © 2015 Pearson Education, Inc. Stimulation produces depolarization of cell o Sweet, bitter, and umami stimuli . G proteins o Gustducins 17-2 Taste (Gustation) End Result of Taste Receptor Stimulation o Release of neurotransmitters by receptor cell . Dendrites of sensory afferents wrapped by receptor membrane . Neurotransmitters generate action potentials in afferent fiber 17-2 Taste (Gustation) Taste Sensitivity o Exhibits significant individual differences o Some conditions are inherited . For example, phenylthiocarbamide (PTC) o 70 percent of Caucasians taste it but 30 percent do not o Number of taste buds . Begins declining rapidly at age 50 17-3 Accessory Structures of the Eye Accessory Structures of the Eye o Provide protection, lubrication, and support . Include: o The palpebrae (eyelids) o The superficial epithelium of eye o The lacrimal apparatus 17-3 Accessory Structures of the Eye Eyelids (Palpebrae) o Continuation of skin o Blinking keeps surface of eye lubricated, free of dust and debris o Palpebral fissure . Gap that separates free margins of upper and lower eyelids 17-3 Accessory Structures of the Eye Eyelids (Palpebrae) o Medial canthus and lateral canthus . Where two eyelids are connected o Eyelashes . Robust hairs that prevent foreign matter from reaching surface of eye © 2015 Pearson Education, Inc. 17-3 Accessory Structures of the Eye Eyelids (Palpebrae) o Tarsal glands . Secrete lipid-rich product that helps keep eyelids from sticking together 17-3 Accessory Structures of the Eye Superficial Epithelium of Eye o Lacrimal caruncle . Mass of soft tissue . Contains glands producing thick secretions . Contributes to gritty deposits that appear after good night’s sleep o Conjunctiva . Epithelium covering inner surfaces of eyelids (palpebral conjunctiva) and outer surface of eye (ocular conjunctiva) 17-3 Accessory Structures of the Eye Lacrimal Apparatus o Produces, distributes, and removes tears o Fornix . Pocket where palpebral conjunctiva joins ocular conjunctiva o Lacrimal gland (tear gland) . Secretions contain lysozyme, an antibacterial enzyme 17-3 Accessory Structures of the Eye Tears o Collect in the lacrimal lake o Pass through: . Lacrimal puncta . Lacrimal canaliculi . Lacrimal sac . Nasolacrimal duct o To reach inferior meatus of nose 17-3 The Eye Three Layers of the Eye 1. Outer fibrous layer 2. Intermediate vascular layer 3. Deep inner layer 17-3 The Eye Eyeball © 2015 Pearson Education, Inc. o Is hollow o Is divided into two cavities 1. Large posterior cavity 2. Smaller anterior cavity 17-3 The Eye The Fibrous Layer o Sclera (white of the eye) o Cornea o Corneal limbus (border between cornea and sclera) 17-3 The Eye Vascular Layer (Uvea) Functions 1. Provides route for blood vessels and lymphatics that supply tissues of eye 2. Regulates amount of light entering eye 3. Secretes and reabsorbs aqueous humor that circulates within chambers of eye 4. Controls shape of lens, which is essential to focusing 17-3 The Eye The Vascular Layer o Iris . Contains papillary muscles o Change diameter of pupil 17-3 The Eye The Vascular Layer o Ciliary Body . Extends posteriorly to level of ora serrata o Serrated anterior edge of thick, inner portion of neural tunic . Contains ciliary processes, and ciliary muscle that attaches to suspensory ligaments of lens 17-3 The Eye The Vascular Layer o The choroid . Vascular layer that separates fibrous and inner layers posterior to ora serrata . Delivers oxygen and nutrients to retina 17-3 The Eye © 2015 Pearson Education, Inc. The Inner Layer o Outer layer called pigmented part o Inner called neural part (retina) . Contains visual receptors and associated neurons . Rods and cones are types of photoreceptors o Rods . Do not discriminate light colors . Highly sensitive to light o Cones . Provide color vision . Densely clustered in fovea, at center of macula 17-3 The Eye Inner Neural Part o Bipolar cells . Neurons of rods and cones synapse with ganglion cells o Horizontal cells . Extend across outer portion of retina o Amacrine cells . Comparable to horizontal cell layer . Where bipolar cells synapse with ganglion cells 17-3 The Eye Horizontal and Amacrine Cells o Facilitate or inhibit communication between photoreceptors and ganglion cells o Alter sensitivity of retina Optic Disc o Circular region just medial to fovea o Origin of optic nerve . Blind spot 17-3 The Eye The Chambers of the Eye o Ciliary body and lens divide eye into: . Large posterior cavity (vitreous chamber) . Smaller anterior cavity o Anterior chamber . Extends from cornea to iris o Posterior chamber . Between iris, ciliary body, and lens 17-3 The Eye © 2015 Pearson Education, Inc. Aqueous Humor o Fluid circulates within eye o Diffuses through walls of anterior chamber into scleral venous sinus (canal of Schlemm) o Reenters circulation Intraocular Pressure o Fluid pressure in aqueous humor o Helps retain eye shape 17-3 The Eye Large Posterior Cavity (Vitreous Chamber) o Vitreous body . Gelatinous mass . Helps stabilize eye shape and supports retina . 17-3 The Eye The Lens o Lens fibers . Cells in interior of lens . No nuclei or organelles . Filled with crystallins, which provide clarity and focusing power to lens o Cataract . Condition in which lens has lost its transparency 17-3 The Eye Light Refraction o Bending of light by cornea and lens o Focal point . Specific point of intersection on retina o Focal distance . Distance between center of lens and focal point 17-3 The Eye Light Refraction of Lens o Accommodation . Shape of lens changes to focus image on retina o Astigmatism . Condition where light passing through cornea and lens is not refracted properly . Visual image is distorted © 2015 Pearson Education, Inc. 17-3 The Eye Light Refraction of Lens o Image reversal o Visual acuity . Clarity of vision . “Normal” rating is 20/20 17-4 Visual Physiology Visual Physiology o Rods . Respond to almost any photon, regardless of energy content o Cones . Have characteristic ranges of sensitivity 17-4 Visual Physiology Anatomy of Rods and Cones o Outer segment with membranous discs o Inner segment . Narrow stalk connects outer segment to inner segment 17-4 Visual Physiology Anatomy of Rods and Cones o Visual pigments . Is where light absorption occurs . Derivatives of rhodopsin (opsin plus retinal) . Retinal synthesized from vitamin A 17-4 Visual Physiology Color Vision o Integration of information
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