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Special Senses Chapter 8 The special senses are touch, taste, smell, sight, and hearing. Equilibrium is also considered a sense of balance. The eye and vision - Visual stimuli makes up 70% of sensory receptors in the body. Anatomy of the eye A. External Structures a. Eyelids - meet medially/laterally for protection b. Eyelashes - protection from each eyelid c. Meibomian glands - oily lubricant d. Ciliary glands - sweat glands between the eyelashes e. Conjuctiva - lining of the eyelid and eyeball (PINK EYE - inflammation of eye - conjunctivitis) f. Lacrimal glands - release salty tears to flush eyeball and destroy bacteria g. External eye muscles - produce gross eye movements Anatomy of the eye B. Internal Structures a. Eyeball - fluid-filled (humors) hollow sphere b. Sclera - a thick white protective tissue (white of the eye) c. Cornea - transparent covering for the eye that contains various nerve endings d. Choroid layer - a blood-rich covering that contains dark pigment e. Ciliary body - attaches to the lens to help it change shape f. Lens - magnifies the object g. Iris - colored pad of the eye h. Pupil - opening through which light passes (dilates and constricts) Anatomy of the eye B. Internal Structures, continued…. i. Retina - the back lining of the eye j. Rods - black and white receptors on the retina (night vision) k. Cones - color receptors on the retina (X-linked) l. Optic nerve - a nerve that is connected to the brain m. Blind spot - the spot where the optic nerve leaves the eyeball N. Fovea centrally - lateral to the blind spot/contains a lot of Cones O. aqueous humor - clear watery fluid p. Vitreous humor - reinforces the eyeball and gives it structure ("snot") q. Fundus - healthy posterior wall of the eye EYE PROBLEMS 1) Night blindness - abnormal rods that hinder our ability to see at night 2) Color blindness - lack of one or more types of cones (color receptors) - X-linked trait 3) Cataracts - the soft gel-like structure becomes foggy and impairs vision "bright sunlight'' 4) Glaucoma - drainage is blocked and pressure builds up in the eye a. Halos around light b. Headaches c. Blurred vision d. Often caused by smoking. Light passing through the eye can be a different medium (water to air). The image (upside down) refracted as it passes through the retina. Humans have binocular vision (two-eyed have optical tracts that meet at a fixation point) where both eyes point Photopupillary Reflex - protective reflex to changes in bright light (Constriction of pupils - bright light, dilation of pupils - dark light) Problems of Refraction THE EAR - Hearing and Balance Fluids must be moved to stimulate the hearing receptors. Sound vibrations move the fluid to stimulate receptors. Mechanoreceptors respond to physical forces that allow us to range our hearing from about 20-20,000 hertz. Our equilibrium is also in the inner ear and helps us to maintain balance. EAR ANATOMY OUTER EAR 1) Pinna - the actual cartilaginous earlobe 2) external auditory canal - long narrow chamber (1 inch long) that goes by the temporal bone 3) ceruminous glands - skin lined wax producing glands (ear wax) 4) tympanic membrane - "eardrum" - receiver for sound vibrations EAR ANATOMY MIDDLE EAR 1 ) tympanic cavity- small air-filled cavity 2) oval window/round window - membrane opening 3) auditory tube - links middle ear with the throat • a. sore throat can lead to ear infections • b. yawning, chewing gum, swallowing can relieve pressure in the ear 4) ossicles - bones of the middle ear • a. hammer (malleus) • b. anvil (incus) • c. stirrup (stapes) Middle Ear Problems: Otitus Media - the eardrum bulges and is inflamed. Large amounts of pus or fluid can accumulate and surgery (lancing the eardrum) to relieve the pressure. Tubes are put in to help drainage. EAR ANATOMY INNER EAR The inner ear has bony chambers called osseous or bony labyrinth. 1) Osseous - bony chambers • a. Cochlea - snail shaped structure that holds fluid • b. Vestibule - located between cochlea and semicircular canals. The connection point of the vestibulochlear nerve. • c. Semicircular canals - balance of fluid motion The bony labyrinth is filled with plasmalike fluid called perilymph and thicker fluid called endolymph. Inner Ear EQUILIBRIUM Your equilibrium responds to certain movements of the head. The equilibrium receptors of the inner ear are sometimes called vestibular apparatus can be static or dynamic equilibrium. http://pro.corbis.com/images/42-17799670.jpg?size=67&uid=%7B7EC65E23-7FD8-4F91-95DF-F9FA7B85FDF8%7D HOW DO WE HEAR?? Mechanisms of Hearing: Within the cochlea, the organ of Corti contains hearing receptors (hair cells) that allow us to hear. Sound waves reach the cochlea through vibrations of the eardrum, ossicles (bones of the middle ear), oval window, and movement of fluid in the inner ear. The force of the bones in the middle ear set the fluid in motion. The hair cells of the Organ of Corti are set into motion by beating with the vibrations. These vibrations are transmitted along the cochlear nerve. Excitation of Hair Cells in the Organ of Corti Figure 15.28c Hearing Defects 1) Deafness - loss of or total inability to hear sounds a. Conduction - interference of sound waves by otitus media, fusion of the ossicles, and buildup of ear wax. b. Sensorimental deafness - degeneration or damage of the receptor cells 2) Equilibrium - nausea, dizziness, and problems maintaining balance 3) Meniere's syndrome - symptoms are nausea, vertigo, and they are prescribed motion sickness drugs. Chemical Senses senses – gustation (taste) and olfaction (smell) Smell and taste compliment each other and have a wider range of sensitivity. Their chemoreceptors respond to chemicals in aqueous solution Chemical Taste – to substances dissolved in saliva Smell – to substances dissolved in fluids of the nasal membranes Taste Buds Most of the 10,000 or so taste buds are found on the tongue Taste buds are found in papillae of the tongue mucosa Papillae come in three types: filiform, fungiform, and circumvallate Fungiform and circumvallate papillae contain taste buds Taste Buds Anatomy of a Taste Bud Each gourd-shaped taste bud consists of three major cell types Supporting cells – insulate the receptor Basal cells – dynamic stem cells Gustatory cells – taste cells Taste Sensations There are five basic taste sensations Sweet – sugars, saccharin, alcohol, and some amino acids Salt – metal ions Sour – hydrogen ions Bitter – alkaloids such as quinine and nicotine Umami – elicited by the amino acid glutamate Physiology of Taste In order to be tasted, a chemical: Must be dissolved in saliva Must contact gustatory hairs Binding of the food chemical: Depolarizes the taste cell membrane, releasing neurotransmitter Initiates a generator potential that elicits an action potential Influence of Other Sensations on Taste Taste is 80% smell Thermoreceptors, mechanoreceptors, nociceptors also influence tastes Temperature and texture enhance or detract from taste Sense of Smell The organ of smell is the olfactory epithelium, which covers the superior nasal concha Olfactory receptor cells are bipolar neurons with radiating olfactory cilia Olfactory receptors are surrounded and cushioned by supporting cells Basal cells lie at the base of the epithelium OLFACTORY SPECIAL SENSES 1) Olfactory receptors - are located at the roof of each nasal caviler so sniffing and smelling intensifies the smell receptors 2) Olfactory hairs - neurons on long cilia that stick out from the nasal epithelium and are bathed by a layer of clear mucus. 3) Olfactory nerve - connected to the olfactory part of the brain. Olfactory becomes a part of our memory EX: Mom's cooking Special Senses: Problems 1 ) Strabismus - ''crossed eyes'' - caused by weak eye muscles. Correction: surgery, eye exercises 2) Rubella - ''German Measles'' - congenital blindness Correction: vaccination/MMR 3) Gonorrhea - baby's eyes are infected with bacteria 4) Conjunctivitis - ''pink eye'' - eyes are red, swollen, and produce pus 5) Presbyopia - ''old age vision'' - the decreasing of lens elasticity