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Biology 232 Human Anatomy and Physiology Chapter 17 Lecture Outline SPECIAL SENSES – sensory receptors in complex sensory organs OLFACTION – sense of smell; chemoreceptors in olfactory epithelium odorants – molecules that stimulate olfaction; hundreds of primary odors Anatomy of Olfactory Epithelium 3 types of cells: 1) olfactory receptors – first-order neurons bipolar neurons with 1 knob-shaped dendrite with olfactory cilia cilia have receptors for odorants olfactory nerve – bundled axons extending through cribriform plate (olfactory receptors live about 1 month) 2) supporting cells – columnar epithelium; support, nourish, and electrically insulate olfactory receptors 3) basal stem cells – divide and differentiate to produce new receptors olfactory (Bowman’s) glands – in underlying connective tissue; secrete mucus on surface – dissolves odorant molecules (only odorants dissolved in mucus can stimulate receptors) Physiology of Olfaction odorants dissolve in mucus odorants bind to receptors on olfactory cilia, which produce receptor potentials threshold potential produces an action potential, which propagates along the olfactory nerve, through cribriform plate (olfactory threshold is low – as little as 4 odorant molecules) olfactory nerves (cranial nerve I) synapse in olfactory bulbs with second-order neurons olfactory tract – second-order neurons to primary olfactory area in medial temporal lobe axon collaterals also run to: limbic system & hypothalamus – emotion and memory frontal lobe – association area for odor identification adaptation – occurs rapidly at first, then slows olfactory receptors adapt little central adaptation occurs in the olfactory bulbs 1 GUSTATION – sense of taste; chemoreceptors in taste buds on papillae of tongue (some on pharynx) tastants – molecules that stimulate gustation (must dissolve in saliva) 5 Primary Tastes: sour, sweet, salty, bitter umami – meaty or savory (watery) taste is augmented by olfaction and tactile sensations Papillae of Tongue: circumvallate papillae – about 12 large, circular structures on proximal tongue; each has up to100 taste buds fungiform papillae – mushroom-shaped; scattered over tongue; each has about 5 taste buds filiform papillae – thread-like; scattered over tongue; no taste buds; have tactile receptors – detect texture of foods Anatomy of Taste Buds – oval structures in walls of papillae 3 types of cells: gustatory (taste) cells – specialized receptor cells gustatory hairs – long microvilli with tastant receptors taste pore – opening in taste bud; gustatory hairs pass through base of gustatory cell synapses with first-order neuron (gustatory cells live about 10 days) supporting (transitional) cells – surround gustatory receptors differentiate to form new gustatory receptors basal cells – divide and differentiate to form supporting cells Physiology of Gustation tastants dissolve in saliva tastants stimulate gustatory hairs, producing receptor potentials (gustatory receptors are more sensitive to some tastants) receptor potentials trigger synaptic vesicles to release neurotransmitters into synaptic cleft neurotransmitters bind to receptors on first-order neuron (first-order neurons have highly branched dendrites synapsing with many gustatory receptors; different tastes activate different groups of neurons) first-order neurons project via cranial nerves VII, IX, X to medulla second-order neurons to thalamus third-order neurons to primary gustatory area 2 VISION – sense of sight; photoreceptors in retina of eyes ophthamology – branch of medicine dealing with diseases and disorders of eye optometry – licensed practice for improvement of vision, and detection and prevention of associated disorders Accessory Structures of the Eye eyelids (palpebrae) – skin flaps that protect eye lacrimal caruncle – contains sebaceous & sweat glands Meibomian glands – modified sebaceous glands of eyelids lubricate lids, prevent sticking together conjunctiva – protective mucous membrane on surface of eye and inner eyelids eyelashes and eyebrows – shade and protect eyes ciliary glands – sebaceous glands of eyelashes sty – infected ciliary gland lacrimal apparatus – cleans, lubricates, and protects eye lacrimal glands – produce tears (watery fluid containing salts, mucus, lysozyme – bactericide) nasolacrimal duct – drains tears into nasal cavity crying – parasympathetic response to sadness or happiness extrinsic eye muscles – move eyeball; innervated by cranial nerves III, IV, VI superior rectus – upward rotation inferior rectus – downward rotation lateral rectus – lateral rotation medial rectus – medial rotation superior and inferior obliques – stabilize eyeball Anatomy of the Eye– 1 inch diameter; recessed in orbit, only anterior 1/6 visible hollow ball composed of 3 layers 3 layers of eye: 1) fibrous tunic – superficial layer cornea – anterior transparent portion avascular, different curvature helps focus vision 3 layers of cornea: outer - nonkeratinized stratified squamous epithelium middle – mainly matrix, layers of collagen inner - simple squamous epithelium sclera – “white” of eye; dense connective tissue which gives rigid shape to eyeball; attachment site for extrinsic muscles 2) vascular tunic (uvea) – middle layer choroid – posterior portion; highly vascular - provides nutrients to retina 3 iris – anterior portion; regulates light entering eye; ANS controls pupil – opening in iris where light enters eye pupillary constrictor muscle – decrease pupil diameter parasympathetic response pupillary dilator muscles – increase pupil diameter sympathetic response ciliary body - between uvea and iris ciliary processes – posterior epithelial folds which produce aqueous humor suspensory ligaments – attach ciliary processes to lens ciliary muscle – focuses lens 3) neural tunic (retina) – inner layer on posterior 3/4 of eyeball location of visual receptors ophthalmoscope – instrument for viewing retina optic disc – optic nerve (cranial nerve II) and central retinal artery and vein pass through eye wall; blind spot 2 layers of retina: pigmented layer – outer layer; epithelial cells contain melanin which absorbs stray light neural layer – inner surface layer; contains photoreceptors and cells which process visual input before passing it to optic nerve 3 cell layers of neural layer: photoreceptor layer – outermost layer rods (125mil) – very sensitive to low light black and white vision only found mainly in peripheral retina disorders = night blindness cones (6mil) – need more light for excitation give sharper vision in color main visual receptors found mainly in center of retina disorders = color blindness macula lutea – center of retina; no rods central fovea – central depression; 1 layer highest concentratioin of cones area of sharpest vision bipolar cell layer – middle layer; adjusts contrast of image bipolar cells, horizontal cells, amacrine cells ganglion cell layer – inner layer cell bodies of first-order neurons (CN II) axons cross retinal surface to optic disc 4 Lens – transparent, avascular ball composed of layers of transparent proteins (crystallins) elastic connective tissue capsule rebounds to round shape cataract – opacity of lens or its capsule which obscures vision Lens Divides Eye Into 2 Cavities: 1) anterior cavity – anterior to lens anterior chamber – between cornea and iris posterior chamber – between lens and iris aqueous humor – watery fluid in anterior cavity nourishes lens and cornea ciliary processes – capillaries which filter blood to produce aqueous humor scleral venous sinus – drains excess aqueous humor from eye 2) vitreous chamber – posterior to lens vitreous body – thick, jelly-like substance that fills chamber and holds retina in place forms in embryo, not replaced intraocular pressure – pressure in eye maintained by aqueous humor; maintains shape of eyeball glaucoma – eye disease characterized by increased intraocular pressure due to decreased drainage of aqueous humor PHYSIOLOGY OF VISION photoreceptors – specialized light receptor cells rods and cones (named for shape of outer segment) rods – detect presence or absence of light cones – detect different wavelengths (colors) of light photopigments – organic molecules that absorb light 2 components of photopigments: retinal – vitamin A derivative that absorbs light and changes shape activates a chain of reactions that result in production of receptor potentials opsins (4 types) – glycoproteins that promote absorption of different wavelengths of light rhodopsin – rods; absorbs any visible light 3 cone photopigments – absorb blue, green, or red light wavelengths light and dark adaptation – period of time required for pigments to shift between light and dark function; caused by differing receptor sensitivities and regeneration times 5 bleaching and regeneration cycles – after absorbing light, photopigments breakdown and are rebuilt using energy from ATP rhodopsin regenerates slowly, while cone photopigments regenerate quickly light adaptation – going from dark to light vision due mainly to cones; fairly rapid adaptation dark adaptation – going from light to dark vision due mainly to rods; slow adaptation receptor potentials processed by bipolar cells and horizontal and amacrine cells; increase sensitivity and contrast, and assist in differentiating colors ganglion cells (first-order neurons)receive inhibitory and excitatory neurotransmitter signals from bipolar and amacrine cells; when threshold stimulus is reached, action potentials are triggered and conducted via axons to the optic disc optic nerves formed by bundled axons of ganglion cells optic chiasm – optic nerves converge and half of axons cross over optic tracts run to thalamus and synapse with second-order neurons second-order neurons project to primary visual area of occipital lobes cerebral hemispheres process information from opposite visual field binocular vision – depth perception due to overlap of visual fields Image Formation – 3 processes involved 1) Refraction – bending of light rays as they pass through substances of differing densities cornea – 75% of refraction lens – 25% ; varies due to focusing (accommodation) produces inverted image on retina (upside-down and left-right reversal); brain interprets correct orientation 2) Accommodation – focusing light rays on central fovea of retina by changing curvature of lens = changing refraction ciliary muscle – circular muscle contraction reduces tension on lens = lens more round relaxation increases tension on lens = flattens lens distant vision (20 ft or more) – parallel light rays; focus on retina with relaxed ciliary muscle = flattened lens (no work) near vision (less than 20 ft) – divergent light rays; require more refraction to focus image on retina contracted ciliary muscle = rounder lens (work required) 6 near point of vision – closest point that you can focus; depends on elasticity of lens presbyopia – loss of elasticity of lens with age children – 3-4 inches age 40 – 8 inches age 60 – 31 inches constriction of pupil aids in focusing near vision – decreases number of divergent light rays entering pupil 3) Convergence – associated with binocular vision; as object moves closer eyes must rotate medially to focus it centrally Refraction Abnormalities – due to misshaped eyeball or lens emmetropic eye (normal) – distant objects focused on retina myopic eye (near-sighted) – eyeball too long, unable to focus on distant objects; correct with less refraction (diverging lens) hyperopic eye (far-sighted) – eyeball too short, unable to focus on close objects; correct with more refraction (converging lens) astigmatism – irregular curvature of cornea or lens HEARING AND EQUILIBRIUM otoscope – instrument for inspecting the ears Anatomy of the Ear – 3 main regions 1) external ear – collects and channels sound waves into ear auricle – funnel of elastic cartilage external acoustic canal – leads from auricle to eardrum; 1 inch canal in temporal bone (external auditory meatus) ceruminous glands – specialized sebaceous glands; associated hairs near external opening; protect ear from foreign material cerumen – ear wax tympanic membrane (eardrum) – partition between external auditory canal and middle ear; thin, semitransparent membrane composed of 3 layers: outer – epidermis middle – connective tissue with collagen & elastic fibers inner – simple cuboidal epithelium 2) middle ear – air-filled cavity in temporal bone; lined with epithelium auditory ossicles – 3 smallest bones in body; articulate by synovial joints suspended across middle ear by ligaments malleus (hammer) – attached to inner tympanic membrane; articulates with incus 7 incus (anvil) – middle bone; articulates with malleus and stapes stapes (stirrup) – articulates with incus; periosteum of bone attaches to the oval window (opening to inner ear) 2 skeletal muscles – protect ear from loud noises tensor tympani muscle – attached to malleus stapedius muscle – attached to stapes round window – membrane-covered opening to inner ear Eustachian (auditory) tube – middle ear to nasopharynx opens to equalize air pressure in middle ear otitis media – middle ear infection; bacteria enter through auditory tube ` 3) inner ear – location of organs for hearing and equilibrium bony labyrinth – series of cavities in temporal bone that enclose membranous organs of hearing and equilibrium perilymph – fluid similar to CSF within bony labyrinth 3 regions of bony labyrinth: 1) vestibule – central portion 2) 3 semicircular canals – 90 degrees to each other 3) cochlea (snail-shaped) – cochlear duct (part of membranous labyrinth) divides into 2 channels vestibular duct – begins at oval window, ends at tip of cochlea tympanic duct – begins at tip of cochlea, ends at round window membranous labyrinth – series of membranous sacs and tubes in bony labyrinth endolymph – fluid within membranous labyrinth 3 regions of membranous labyrinth: 1) saccule & utricle – 2 sacs in vestibule; function in equilibrium 2) 3 semicircular ducts – in semicircular canals; function in equilibrium 3) cochlear duct – in cochlea; functions in hearing vestibular membrane – between cochlear duct and vestibular duct tectorial membrane – stiff membrane in cochlear duct basilar membrane – between cochlear duct and tympanic duct organ of Corti – sensory organ on basilar membrane hair cells – mechanoreceptors stereocilia – hairs which produce receptor potentials when bent against tectorial membrane 8 PHYSIOLOGY OF HEARING sound waves – alternating ripples of high and low pressure air originating from a vibrating object frequency – number of waves/second (Hz) high frequency = high pitch audible range 20-20,000 Hz amplitude (size) – loudness; measured in decibels (dB) >90dB hearing protection is required; damages hair cells Pathway for Hearing: sound waves funneled into external ear and strike tympanic membrane producing vibrations varying in frequency and amplitude malleus transmits vibrations to incus, incus to stapes, and stapes to oval window (mechanically amplified) vibrations at oval window membrane produce pressure waves in perilymph of cochlea perilymph pressure waves travel from vestibular duct to tympanic duct to round window (round window prevents echo) pressure waves produce vibrations of basilar membrane hair cells bend against tectorial membrane each segment of basilar membrane vibrates at a different wavelength – brain interprets as pitch hair cells (specialized receptor cells) produce receptor potentials which trigger release of neurotransmitter (number of hair cells stimulated determines loudness) neurotransmitter triggers action potential in first-order neurons of cochlear branch of c.n.VIII, which project to medulla integration occurs in the inferior colliculi for reflexes impulses project to the thalamus, then to the auditory cortex in the temporal lobe EQUILIBRIUM (Balance) vestibular apparatus – organs of equilibrium (saccule, utricle, semicircular ducts) Static Equilibrium – detect body position relative to gravity saccule and utricle (otolithic organs) maculae – thickened regions in walls of each which are perpendicular to each other hair cells with stereocilia and 1 large kinocilium otolithic membrane – glycoprotein layer resting on hair cells otoliths – calcium carbonate crystals 9 as head tilts, otoliths (due to gravity) pull otolithic membrane downhill, bending stereocilia bending stereocilia causes receptor potentials in hair cell bending towards kinocilium excites hair cell bending away from kinocilium inhibits hair cell neurotransmitter triggers action potential in first-order neurons of vestibular branch of c.n.VIII Dynamic Equilibrium – detect rotational head movements semicircular ducts – lie at right angles to each other in 3 planes anterior and posterior ducts – sagittal and frontal planes lateral duct – transverse plane ampulla - dilated portion; contains sensory organ crista – elevation with hair cells cupula – gelatinous material coating hair cells as head moves, ducts and their structures move, but endolymph & cupula inside lag (due to inertia) and bend hair cells bending hair cells produces receptor potentials action potentials in vestibular branch of c.n.VIII (saccule and utricle also involved in dynamic equilibrium) vestibular branch of c.n. VIII projects to brain stem and cerebellum complex integration pathways monitor position and movements and use input to coordinate movements of eyes, head & neck, and adjust muscle tone to maintain balance 10