Nervous System: Special Senses(Chapter 17)Lecture MaterialsforAmy Warenda Czura, Ph.D.Suffolk County Community CollegeEastern CampusPrimary Sources for figures and content:Marieb, E. N. Human Anatomy & Physiology 6th ed. San Francisco: Pearson BenjaminCummings, 2004.Martini, F. H. Fundamentals of Anatomy & Physiology 6th ed. San Francisco: PearsonBenjamin Cummings, 2004.Special SensesFive special senses: smell, taste, sight, hearing, equilibriumAll involve special sensory receptors-distinct receptor cells-housed in complex sensory organs or unique epithelial structuresOlfaction (smell)olfactory organs = olfactory epithelium-housed in nasal cavity, inferior surface ofcribriform plate and superior nasal conchaeOlfactory Epithelium Components1. olfactory receptor cells-bipolar neurons-chemoreceptors-bind and respondto odorants(smellchemicals)2. supporting cells-simple columnarepithelium3. basal cells-stem cells-replace olfactory receptor cells every 60 days4. lamina propria-areolar CT-supports epithelium and neurons-contains olfactory glands for mucus production: mucus covers surfaceof olfactory epitheliumOlfactory receptor cells-single dendrite at apicalsurface of epithelium-dendrite ends in knobcovered in olfactory cilia-cilia extend into mucus-odorant binding proteins oncilia bind chemicalodorant molecules thathave diffused into mucus-each receptor cell has only one type ofodorant binding protein but each protein binds several odorants-humans: ~1000 different odorant binding proteins, distinguish ~10,000 different odors-axon from each cell passesthrough olfactory foraminaof cribriform plate tosynapse on olfactory bulbs(axons =olfactory nerves)Amy Warenda Czura, Ph.D.1SCCC BIO130 Chapter 17 Lecture NotesOlfactory Signaling (on handout)Signaling1. Odorant binds odorant binding protein on olfactory receptor cell cilia in mucus2. G-protein is activated which activates adenylate cyclase3. ATP is converted into cAMP4. cAMP causes sodium channels to open resulting in depolarization5. If threshold is reached and action potential is transmitted to the CNS olfactory bulbs6. The nervous impulse from the olfactory bulbs travels down the olfactory tracts to be routed to:a. olfactory cortex of the cerebrum for interpretation (* smell is the only type of sensory info that reaches the cerebral cortex without first synapsing in the thalamus: no sensory dampening!)b. hypothalamus and limbic systems to elicit emotional response to odors-the signaling can also stimulate reflexes for salivation, digestive secretion, sneezing and coughing-olfactory pathways converge and are subject to rapid central adaptationOlfactory disorders:Uncinate fits = olfactory hallucinations-distorted sense of smell due to damage of olfactory pathways, epilepsy, or migrainesAnosmias = “without smells”-loss of sense of smell-due to head injury, inflammation, age, or zincdeficiency(zinc necessary for growth of basal cells toreplace receptor cells)Gustation (taste)gustation organs =taste buds~10,000 total-most located on tongue associated with lingual papillae (friction bumps)-small number on oral surfaces: soft palate, inner cheeks, pharynx, epiglottisTaste Bud Components50-100 epithelial cellsof two types:1. gustatory cells-taste receptor cells-in various stages of maturity-mature have long microvilli = gustatory hairsthat function as chemoreceptors-gustatory hairs bind tastants (taste chemicals)-each gustatory cell is wrapped in sensory dendrites2. basal cells-stem cells-replace gustatorycells every7-10 days-taste buds located deep in tongue epitheliumwith taste hairs protruding into taste pore5 Primary Taste Sensations1. sweet: sugars, alcohols, some amino acids2. sour: acids3. salty: metal ions4. bitter: alkaloids5. umami “delicious”: amino acid glutamate (beef taste) (MSG binds this)Tastes and cravings drive dietary needs:umami ! proteinssugar & salty ! carbs and mineralssour ! vitamin CTastes also protect:-most toxins are bitterAmy Warenda Czura, Ph.D.2SCCC BIO130 Chapter 17 Lecture NotesGustatory Signaling (on handout)Vision (sight)vision organs = eyes-70% of total body receptors-50% of cerebral cortex involved in visionprocessingAccessory structures(on handout)diplopia = “double vision”-failure to coordinate movement of eyes resulting in two different visual fields-due to paralysis, weak muscles, intoxicationstrabismus = “cross eyed”-congenital weakness of external eye muscles-treated with exercises or surgeryThe Eye-fluid filledsphere-wall consists of three layers:1. outer fibrous tunic2. intermediate vascular tunic3. inner neural tunic-interior divided into two cavities (anterior, posterior) by the lens-cavities contain fluids called humors: maintain shape of eye1. Fibrous tunic-dense fibrous CT-avascularA. Sclera (“white of eye”)-posterior 5/6ths-functions to maintain eye shape and as attachment for eye musclesAmy Warenda Czura, Ph.D.3SCCC BIO130 Chapter 17 Lecture Notes-continuous with epineurium of optic nerveand dura mater of brainB. Cornea-anterior 1/6th-clear, allows light to enter eye-high concentration of pain receptors-damage = scaring = inhibit visionCorneal transplant: due to lack of blood supply there are no immune cells, no need to tissue type match2. Vascular tunic = uvea-contains blood and lymphatic vessels for allthree tunics-consists of three regionsA. Choroid-lines posterior 5/6ths-pigmented dark brown by melanocytes toprevent light scatterB. Ciliary body-circular smooth muscles that function to focus lens and center it posterior to pupil-attached to lens by suspensory ligaments-secretes fluid that fills anterior chamber ofeyeC. Iris-anterior portion of uvea-has central opening called pupil-smooth muscle + elastic fibers-regulate pupil size to control light level entering eye:-parasympathetic stimulation = circular muscles contract ! pupil size decreases-sympathetic stimulation = radial musclescontract ! pupil size increases-color variations depend on amount and location of melanin:-more on both sides = brown-less on posterior only = blue3. Neural tunic = retina-two partsA. Pigmented layer-melanin-rich simple cuboidal epitheliumin contact with choroid-absorbs light to prevent scatter-stores Vitamin A-capable of phagocytosisB. Neural layer-five types of neurons1. photoreceptors:-detect light photonsa. rods = dim light, no color, peripheralvisionb. cones = color, sharp visionAmy Warenda Czura, Ph.D.4SCCC BIO130 Chapter 17 Lecture Notes2. horizontal cells: visual processing3.