Lesson 2: Special SensesAn Introduction to the Special Senses:Five Special Senses: olfaction, gustation, vision, equilibrium, hearingWhich one(s) depend upon mechanoreceptors? Vision, equilibrium, hearingWhich one(s) depend upon chemoreceptors? Olfaction and gustation17-1: Smell (olfaction)Olfactory Organs:Provide sense of smellLocated in nasal cavity on either side of nasal septumMade up of two layers:1. Olfactory epithelium2. Lamina propriaLayers of Olfactory Organs:Olfactory epithelium contains:1. Olfactory receptor cells2. Supporting cells3. Basal (stem) cells- regenerates olfactory receptor cellsLamina propria contains:1. Areolar tissue2. Blood vessels3. Nerves4. Olfactory glands-form mucusOlfactory Glands:Secretions coat surfaces of olfactory organsOlfactory receptors:Highly modified neuronsOlfactory Reception:Involves detecting dissolved chemicals as they interact with odorant-binding proteins on cell membrane of olfactory receptor cellOlfactory Pathways:Axons leaving olfactory epithelium-axons collected into 20 or more bundlesPenetrate cribriform plate of ethmoidReach olfactory bulbs of cerebrum where first synapse occursAxons leaving olfactory bulb:Travel along olfactory tract to reach olfactory cortex, hypothalamus, portions of limbic systemArriving information reaches information centers without first synapsing in thalamusOlfactory Discrimination:Can distinguish thousands of chemical stimuliCNS interprets smells by the pattern of receptor activityOlfactory Receptor Population:Considerable turnover (receptor cells replenished by basal cells)Number of olfactory receptors (and resulting sense of smell) declines with age17-2: Taste (Gustation)Gustation:Provides information about the foods and liquids consumedTaste Receptors (gustatory receptors):Distributed on tongue and portions of pharynx and larynxClustered into taste budsAssociated with epithelial projections (lingual papillae) on superior surface of tongueThree Types of Lingual Papillae:1. Filiform papillaeDo not contain taste budsProvide friction2. Fungiform papillaeContain 5 taste buds each3. Circumvallate papillaeContain 100 taste buds eachTaste buds Contain:1. Basal cells2. Gustatory cellsExtend taste hairs through taste poreSurvive only 10 days before replacementMonitored by cranial nerves that synapse within the medulla oblongataThen on to thalamus and primary sensory cortexCN medulla thalamus PSCGustatory Discrimination:Four Primary Taste Sensations:1. Sweet2. Salty3. Sour4. BitterAdditional human taste sensations1. UmamiReceptors sensitive to amino acids, small peptides, and nucleotidesDetects characteristic of beef/chicken broths and Parmesan cheese2. WaterDetected by water receptors in the pharynxDissolved chemicals contact taste hairsBind to receptor proteins of gustatory cellSalt and sour receptorsChemically-gated ion channelsStimulation produces depolarization of cellSweet, bitter, and umami stimuliBinds to membrane receptor protein to activate G proteinsEnd Result of Taste Receptor Stimulation:Release of neurotransmitters by receptor ellNeurotransmitters generate action potentials in afferent fiberTaste Sensitivity:Exhibits significant individual differences1000x more sensitive to acids (sour taste) than sweet/salty, 100x more sensitive to bitter than acidsWhy? Because a lot of poisonous things are bitter so it is a defense mechanism by the bodySome conditions are inheritedFor example, phenylthiocarbamide (PTC)- 70% of Caucasians taste it but 30% do notNumber of taste buds begins declining rapidly by age 5017-3: Accessory Structures of the EyeAccessory Structures of the Eye:Provide protection, lubrication, and supportInclude:1. The palpebrae (eyelids)- continuation of skinBlinking keeps surface of eye lubricated, free of dust and debrisTarsal glands- secrete lipid-rich product that helps keep eyelids from sticking together2. The superficial epithelium of eye-includes:Lacrimal caruncle- contains glands producing thick secretionsContributes to gritty deposits that appear after good night’s sleepConjunctiva - Epithelium covering inner surfaces of eyelids (palpebral conjunctiva) and outer surface of eye (ocular conjunctiva).Inflammation (of the conjunctiva)= conjunctivitis/pinkeye (redness caused by infection, allergy, chemical irritation)3. Lacrimal apparatus- produces, distributes, and removes tearsLacrimal gland (tear gland)- secretions contain lysozyome (=an antibacterial enzyme)Tears:Collect in the lacrimal lake at the medial canthusPass through:Lacrimal punctaLacrimal canaliculiLacrimal sacNasolacrimal ductTo reach inferior meatus of nose17.3: The Eye:Eyeball:HollowDivided into 2 cavities:1. Large posterior cavity - Filled with vitreous humor2. Smaller anterior cavity - Filled with aqueous humorConsists of the anterior (before the iris) and posterior (after the iris) chambersThree Layers of the Eye:1. Outer Fibrous Layer2. Intermediate Vascular Layer3. Deep Inner Layer1. The Outer Fibrous Layer:Cornea (transparent anterior region)Sclera (white of the eye)Corneal limbus (border between cornea and sclera)2. The Intermediate Vascular Layer (Uvea):Functions:1. Provides route for blood vessels and lymphatics that supply tissues of eye2. Regulates amount of light entering eye3. Secretes and reabsorbs aqueous humor that circulates within chambers of eye4. Controls shape of lens, which is essential to focusingComponents:Iris - Contains papillary musclesSympathetic and parasympathetic innervations change the diameter of pupil by stimulating the pupillary dilator or constrictor, respectivelyCiliary Body - Contains ciliary processes and ciliary muscle that attaches to suspensory ligaments of lensControls lens position and shapeChoroid - Delivers oxygen and nutrients to retina3. The Deep Inner Layer:Outer layer called pigmented part - absorbs light that passes through neural part, prevents rebounding of lightInner called neural part (retina)Contains visual receptors and associated neuronsRods and cones are types of photoreceptorsRodsDo not discriminate light colorsHighly sensitive to light – used in low light (night time)ConesProvide color visionDensely clustered in fovea, at center of maculaInner Neural Part:Bipolar cellsNeurons that allow rods and cones to synapse with ganglion cellsHorizontal cellsExtend across outer portion of retinaAmacrine cellsComparable to horizontal cell layerWhere bipolar cells synapse with ganglion cellsHorizontal and Amacrine Cells:Alter sensitivity of
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