CHAPTER 17 THE SPECIAL SENSES AN INTRODUCTION TO THE SPECIAL SENSES FIVE SPECIAL SENSES 1 Olfaction o Chemoreceptor 2 Gustation 3 Vision o Chemoreceptor o Modified Mechanoreceptor 4 Equilibrium o Mechanoreceptors 5 Hearing o Mechanoreceptors SMELL OLFACTION Olfactory Organs Provide sense of smell Located in nasal cavity on either side of nasal septum Made up of two layers o o 1 Olfactory epithelium contains olfactory receptor cells supporting cells basal stem cells to regenerate olfactory receptor cells exposed into nasal cavity 2 Lamina propria contains areolar connective tissue blood vessels nerves olfactory glands produces mucus which covers olfactory epithelium to prevent drying out NOTE When you smell something little molecules from that food ex Pizza bind to receptors on the olfactory dendrites and this alters the action potentials generated by the olfactory fibers Olfactory Glands Olfactory Receptors Secretions coat surfaces of olfactory organs Highly modified neurons Olfactory reception Involves detecting dissolved chemicals as they interact with odorant binding proteins o Odorant binding proteins located on the cell membrane of olfactory receptor cell Olfactory Pathways more bundles Axons leaving olfactory epithelium Collected into 20 or Penetrate cribriform plate of ethmoid bone o o Reach olfactory bulbs of cerebrum where first synapse occurs Axons leaving olfactory bulb o Travel along olfactory tract to reach olfactory cortex hypothalamus and portions of limbic system associated with triggering memory circuits Arriving information reaches information centers without first synapsing in thalamus Olfactory Discrimination Can distinguish thousands of chemical stimuli CNS interprets smells by the pattern of receptor activity Olfactory Receptor Population Considerable turnover receptor cells replaced by basal cells Number of olfactory receptors and sense of smell declines with age this is why old people have such a strong smell they use too much fragrance TASTE GUSTATION Gustation Provides information about the foods and liquids consumed Taste Receptors Gustatory Receptors Are distributed on tongue on taste buds and portions of pharynx and larynx Clustered into taste buds o Associated with epithelial projections lingual papillae on superior surface of tongue Four Types of Lingual Papillae Filiform papillae o Do not contain taste buds o Provide friction to help you grab food with tongue Fungiform papillae o Contain about five taste buds each Vallate papillae o Contain 100 taste buds each Foliate papillae o Along sides of tongue Taste Buds Contain o Basal cells which replace damaged gustatory receptor cells o Gustatory receptor cells Extend taste hairs through taste pore Survive only 10 days before replacement o Monitored by cranial nerves that synapse within solitary nucleus of medulla oblongata Then on to thalamus and primary sensory cortex Gustatory Discrimination Four primary taste sensations o o o o 1 Sweet 2 Salty 3 Sour 4 Bitter o Umami o Water Substances pass through a passive channel Substances pass through a passive channel Additional Human Taste Sensations Characteristic of beef chicken broths and Parmesan cheese Receptors sensitive to amino acids small peptides and nucleotides Detected by water receptors in the pharynx Gustatory Discrimination Dissolved chemicals contact taste hairs Bind to receptor proteins of gustatory cell Salt and sour receptors o Use chemically gated ion channels Na or H enter through Na or H leak channels Stimulation produces depolarization of cell o Sweet bitter and umami stimuli o Activate G proteins Gustducins End Result of Taste Receptor Stimulation Release of neurotransmitters by receptor cell o Dendrites of sensory afferents wrapped by receptor o Neurotransmitters generate action potentials in membrane afferent fiber Taste Sensitivity it varies more sensitive to acidic sour things than sweet foods Exhibits significant individual differences 1000 times more sensitive to acids sour taste than sweet salty 100 times more sensitive to bitter than acids why Many poisonous toxic compounds are acidic and bitter in taste So this is a survival mechanism Some conditions are inherited o For example phenylthiocarbamide PTC 70 percent of Caucasians taste it but 30 percent do not Number of taste buds begins declining rapidly at age 50 ACCESSORY STRUCTURES OF THE EYE Accessory Structures of Eye Provide protection lubrication and support o o o o Include 1 The palpebrae eyelids continuation of skin Blinking keeps surface of eye lubricated free of dust debris Tarsal glands Secrete lipid rich product that helps keep eyelids from sticking together o 2 The superficial epithelium of eye Lacrimal caruncle Mass of soft tissue containing glands producing thick secretions Contributes to gritty deposits that appear after good night s sleep Conjunctiva Epithelium covering inner surfaces of eyelids palpebral conjunctiva and outer surface of eye ocular conjunctiva Conjunctivitis pinkeye inflammation o 3 The lacrimal apparatus Produces distributes and removes tears Smaller anterior cavity filled with aqueous humor Consists of the anterior chamber anterior to iris and posterior chamber posterior to iris Three Layers of the Eye Outer fibrous layer Sclera white of the eye Cornea transparent anterior region So light can pass through Corneal limbus border between cornea and sclera 2 Intermediate vascular layer UVEA Functions o o o o o o Includes 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 Iris Contains papillary muscles Change diameter of pupil Sympathetic and parasympathetic innervation changes the diameter of pupil by stimulating pupillary dilator sympathetic or constrictor parasympathetic respectively Ciliary body Contains ciliary processes and ciliary muscle that attaches to suspensory ligaments of lens Controls lens position and shape Choroid Delivers oxygen and nutrients to retina Lacrimal gland tear gland lateral not the same as the medial duct o Secretions contain lysozyme an antibacterial enzyme to kill any bacteria that may be in your eye 3 Deep inner layer o NOTE Structures where light goes through are going to be pretty transparent not opaque o NOTE When contracts the lens becomes thicker when relax it becomes thinner o Outer layer called pigmented part
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