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Chapter 16.docx

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University of Toronto Scarborough
Biological Sciences
Ted Petit

Chapter 16 Special Senses • Olfactory Sensations: Smell - Types of cells 1. receptors lie in nasal epithelium of superior portion of nasal cavity a. bipolar neurons 1) distal end is a dendrite with olfactory cilia (hairs), which generate impulses in response to odor molecules 2) axon synapses with another neuron in the olfactory bulb 2. supporting cells a. columnar epithelial cells, secrete mucus 3. basal cells a. between supporting cells b. stem cells that replace old receptor cells about every month 4. olfactory (Bowman's) glands a. produce mucus that empties onto the olfactory epithelium by ducts (odor molecules must dissolve in mucus to be sensed) - Olfactory pathway 1. olfactory bulb neurons receive signals from receptors a. sends signals along olfactory tract to olfactory area on medial surface of temporal lobe, limbic system and part of frontal lobe • Gustatory Sensations: Taste - Taste buds 1. mostly on tongue, some on soft palate, cheeks and pharynx 2. in papillae (elevations on tongue) a. vallate papillae are on back of tongue b. fungiform papillae are scattered over tongue surface c. filiform papillae cover the surface of the tongue but do not have taste buds 3. three kinds of epithelial cells a. gustatory cells are the receptor cells (have microvilli with receptors, substance to be tasted must be dissolved in saliva in a taste pore); they synapse with sensory nerve fibers b. supporting cells c. basal cells, which can differentiate into other cell types 4. five primary taste sensations a. sweet, sour, salty, bitter, umami b. each tends to be sensed on certain areas of tongue, but an individual receptor may respond to more than one kind of taste - Gustatory pathways 1. fibers leading from taste buds are in... a. facial nerves (from anterior 2/3 of tongue) b. glossopharyngeal nerves (from posterior 1/3) c. vagus (from throat and epiglottis) d. The three cranial nerves end in the medulla, from there fibers project to gustatory area in parietal lobe via the thalamus • Visual Sensations and the Eye - Accessory structures of the eye 1. eyebrows a. shade eyes from sunlight, protect from perspiration 2. eyelashes a. protective, when disturbed trigger reflex blinking 3. eyelids (palpebrae) a. upper and lower lids separated by palpebral fissure, they meet at medial and lateral canthi (medial canthus contains lacrimal caruncle with sebaceous and sweat glands) b. tarsal plates - fold of connective tissue that supports lids, contains tarsal glands that produce an oily secretion to lubricate lids and prevent sticking together 4. conjuctiva a. stratified columnar mucous membrane lubricates eye with mucus, has palpebral and ocular layer 5. lacrimal apparatus a. lacrimal glands secrete lacrimal fluid (tears) b. blinking spreads tears to lacrimal canals, which drain to lacrimal sac and nasolacrimal duct, and empties into nasal cavity c. tears clean, protect and lubricate (contain mucus, antibodies, lysozyme) 6. extrinsic eye muscles a. allow movement b. origins are in bones of orbit, insert into outer surface of eyeball - Eyeball structure 1. fibrous tunic a. outer part of eye wall b. dense CT, mostly collagen fibers 1) sclera - opaque, white; protects and shapes the eye, muscles insert 2) cornea - transparent; allows light to enter the eye and bends light; covered by epithelium (outer surface is a protective stratified squamous, inner surface simple squamous) 2. vascular tunic a. middle layer b. choroid 1) nourishes the tunics (has blood vessels) 2) contains melanin that absorbs light and prevents scattering c. ciliary body 1) connects with choroid and retina at ora serrata 2) mostly smooth muscle that controls shape of lens 3) ciliary processes secrete fluid called the aqueous h
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