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CHAPTER 15 SPECIAL SENSES senses • • general senses – – – – widely distributed somatic senses - touch, temperature, muscle spindles visceral senses - from organs no specialized receptor special senses – – – specialized receptor structure located only in head cranial nerves to special centers in brain special senses • • • • • taste smell vision hearing equilibrium Taste • • papillae – – – bumps on tongue fungiform circumvallate filiform taste buds – – – epithelia within papillae gustatory cells actual receptors supporting cells basal cells gustatory pathway • • • • • receptor sensory nerves medulla thalamus cortex smell = olfaction • olfactory epithelium – – • olfactory receptor cells – bipolar cells – olfactory cilia supporting and basal cells superior nasal mucosa receptors olfactory pathway • • • • • • olfactory receptors olfactory nerve (CN I) pass through ??? olfactory bulb olfactory tract axons of mitral cells brain centers – – limbic system piriform lobe of cortex (uncus) EYE • • • • special sense for vision photoreceptors light, color eye = organ to focus light on the receptors specialized cerebral cortex external eye • • • • eyelids conjunctiva lacrimal apparatus extrinsic muscles eyelid = palpebrae • • • • • • • • protect and lubricate tarsal plates levator palpebrae superioris orbicularis oculi medial and lateral canthus (commissure) lacrimal caruncle tarsal glands (Meibomian glands) eyelashes sensory conjunctiva • • • • transparent membrane palpebral conjunctiva bulbar conjunctiva conjunctivitis lacrimal apparatus • • • • • lacrimal gland lacrimal punctum canaliculus lacrimal sac nasolacrimal duct extrinsic eye muscles • • • • • • superior rectus CN III inferior rectus CN III medial rectus CN III lateral rectus CN VI superior oblique CN IV inferior oblique CN III eyeball • 3 layers = tunics : – – – fibrous tunic vascular tunic sensory tunic Fibrous tunic = dense reg. c.t • • sclera – – – cornea – – “white of the eye” support muscle attachment transparent avascular • limbus – junction of sclera to cornea • • • • • choroid blood vessels pigmented (melanin) • ciliary process • ciliary muscle • • • ciliary zonule vascular tunic • ciliary body produces aqueous humor iris smooth muscle controls size of pupil • dilator pupillae dilate pupil • sphincter pupillae constrict pupil pupillary light reflex CN ??? lens • • • • transparent avascular focus light onto retina – via ciliary muscles cataracts = cloudy lens proteins degenerate sensory tunic • • • = retina pigmented layer neural layer – – – photoreceptor cells • rods • cones light peripheral color, acuity central bipolar cells ganglion cells axons = optic nerve retina structures • optic disc optic nerve exit through retina = blind spot • macula lutea center of retina mostly cones • fovea centralis center of macula only cones = focal spot • ora serrata retinae border with ciliary bodies cavities (segments) • • • divided by lens and suspensory ligt. posterior cavity – – vitreous humor holds retina in place anterior cavity – aqueous humor – – nutrients for lens and cornea made by ciliary body anterior cavity • • • • anterior chamber anterior to iris posterior chamber posterior to iris aqueous humor nutrients for lens and cornea made by ciliary body scleral venous sinus = canal of Schlemm drains aqueous humor • Glaucoma visual pathway • retina to occipital lobe : – – – – • • – optic nerve axons of ganglionic cells through optic foramen optic chiasm cross of medial fibers of optic nerves optic tract in brain thalamus lateral geniculate nucleus synapse with thalamic neurons optic radiation axons to occipital cortex retina to other parts of brain : – – – superior colliculi reflex movt of eye muscles pretectal nuclei pupillary reflexes (CNII and III) hypothalamus sleep cycles physics and sight • myopia nearsighted eyeball too long 20 / >20 • hyperopia far sighted eyeball too short 20 / <20 • presbyopia decreased near vision with age weak ciliary muscles , lens • astigmatism varied shaped lens EAR • • 2 special senses (receptors) : – – hearing equilibrium 3 parts : – – – external ear middle ear inner ear external ear • • • auricle = pinna external auditory meatus external auditory canal tympanic membrane eardrum = • vibrates with sound waves middle ear • • • • • = tympanic cavity ossicles – – – malleus contacts tympanic membrane incus stapes medial wall – – middle ear bones increase vibration contacts oval window contacts inner ear oval window round window (vestibular window) (cochlear window) pharyngotympanic tube (= eustachian tube) connects to nasopharynx otitis media inner ear • • 2 receptors : hearing cochlea • equilibrium vestibule and semicircular canals • bony labyrinth cavity within temporal bone filled with perilymph inner ear – – – • cochlea semicircular canals vestibule membranous labyrinth – – – – membranes within bony labyrinth filled with endolymph cochlear duct within cochlea semicircular ducts within semicircular canals utricle within vestibule saccule within vestibule cochlea • • • • • cochlea = cochlear duct spiral cavity of bony labyrinth spiral membranous labyrinth w/in cochlea contains receptors = Organ of Corti 2 chambers next to cochlear duct : scala vestibuli contacts oval window (vestibule) scala tympani contact round window (cochlear) Organ of Corti • • • • • • = spiral organ receptor mechanism hair cells receptor cells – stereocilia contact tectorial membrane basilar membrane supporting cells tectorial membrane cochlear nerve – spiral ganglia VIII to brain cell bodies auditory pathway • • • to temporal lobe – – – – cochlear nerve cochlear nuclei thalamus – temporal lobe to inferior colliculi – auditory reflex to cerebellum – olivary nuclei equilibrium • • • 2 structures : vestibule static equilibrium (vs gravity) linear acceleration semicircular canals dynamic equilibrium rotational acceleration Vestibule • • • • 2 structures of membranous labyrinth : – – utricle horizontal motions saccule vertical motion macula – – – sensory epithelium supporting cells hair cells receptor cells otolithic membrane • otoliths calcium crystals head or spacial movement tilts the otoliths and bend vestibular nerve the hair cells semicircular canals • • 3 planes of space ampulla – – base of each duct crista ampullaris – – cells within ampulla supporting cells hair cells receptor cells cupula gel covering hair cells • rotation of head moves the cupola and bends the hair cells • vestibular nerve equilibrium pathway • • • • vestibular nerve vestibular nuclei medulla cerebellum reflex movement cerebrum parietal lobe conscious awareness of position and movement