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The Senses Terminology Sensation: conscious or subconscious awareness of external or internal body conditions Adaptation: the ability of a stimulus to decrease its sensation over a prolonged period of time. Proprioception: perception of body position Kinesthesia: perception of body movement Perceptions: conscious sensation that you acquire with all of your senses Ex: hearing, seeing, tasting, touching, smelling To feel a sensation… 1. 2. 3. 4. Stimulus must occur Sensory receptor converts the stimulus into an impulse The impulse is conducted to the brain (via sensory or afferent neuron) Brain (control center) integrates the impulse into a sensation (hot, pain, itch, etc.) A look at the pathway Senses can be… General Touch Pressure Temperature Pain Position Special Smell (olfaction) Hearing & Equilibrium Seeing (vision) Tasting (gustation) Classification of Sensations… Be familiar with… Mechanoreceptor (movement) = detect touch, pressure, hearing Thermoreceptor (temperature) = detect temperature changes Photoreceptor (light) = detect light changes Chemoreceptor (chemicals) = detect taste & smell Cutaneous sensations (tactile) Are general senses Senses that affect skin Receptors embedded in dermis Touch Crude = perception of touch Fine = specific information about touch Cutaneous receptors Meissner’s corpuscle: rapid adapting fine touch receptor Hair root plexus: rapid adapting receptor for detecting movement on skin Merkel disks: slow adapting receptor that coincide with Meissner’s corpuscle Ruffini’s corpuscle: slow adapting receptor for detecting stretching & limb movement More cutaneous receptors Pacinian corpuscle: pressure & vibration Nociceptors (free nerve endings): itch, tickle, pain Cold receptors (epidermis): temperatures between 50-105 degrees Fahrenheit Warm receptors (dermis): temperatures between 90-118 degrees Fahrenheit Pain Referred pain: pain usually felt on the skin overlying the affected organ Phantom pain: pain felt in an organ or limb that has been removed Analgesia: pain relief; blocks chemicals that stimulate free nerve endings Special Senses Have an organ devoted to the sense Ear = hearing & equilibrium Eye = vision Nose = olfaction Tongue = gustation Vision Uses more than half of the sensory receptors in the body Accessory structures: Eyebrows & eyelashes = protection eyelids = protection & spread secretions Lacrimal glands = produce tears that contain lysozyme (bactericidal enzyme) Vision specialists Opthalmology: study of eye structure, function, and diseases Optician Optometrist Fits & adjusts lenses Optician duties + Gives eye exams, corrective lens prescriptions Opthalmologist (M.D.) Optometrist duties + Surgical procedures & medication prescriptions The Eye (p. 278, Figure 10.17) 2.5 cm in diameter Exterior has 3 layers (coats = tunics) Outer = fibrous tunic Middle = vascular tunic Cornea: transparent outer covering for bending light as it enters eye; covered by conjunctiva Sclera: white of the eye; gives eye its shape Choroid: lines sclera Ciliary body: secretes aqueous humor; alters lens shape Iris: colored part of eye; regulates pupil (hole) size Inner = retina Lines posterior ¾ of eye; contains photoreceptors (rods = b/w & cones = color) Optic disk = blind spot found here The Eye The Eye Chambers Interior eye (divided by lens) Anterior cavity = contains aqueous humor (watery substance that maintains corneal shape); constantly replaced Posterior cavity = contains vitreous humor (jelly-like fluid that holds retina in place); never replaced More on the eye Binocular vision: seeing 1 image with 2 eyes The eye works like a camera Light is refracted (bent) as it enters Image is inverted on retina Brain reverses image to recognize it Pathway: light rods & cones bipolar cells ganglion cells optic nerve optic chiasm optic tract thalamus occipital lobe of brain The eye camera Eye disorders Myopia: near sightedness Hypermetropia: far-sightedness Presbyopia: old-sightedness which is usually farsighted; acquired ~ 40 years Astigmatism: irregular curvature of cornea or lens Color-blindness: inherited inability to see certain colors due to missing cones; males affected more often (sexlinkage) Cataracts: clouding of lens; may cause blindness Glaucoma: high or low anterior eye (ocular) pressure; leading cause of blindness in the U.S. Myopia Hypermetropia Glaucoma Cataract Olfaction Sense of smell Uses the nose Receptors embedded in mucosa Pathway: olfactory receptors olfactory nerves olfactory bulbs olfactory tract temporal lobe of brain Gustation Sense of taste Uses the tongue (and nose) 4 classes of taste Sweet (tip) Salty (sides, anterior) Sour (sides, posterior) Bitter (back) Gustation continued Taste buds ~10,000 on roof of mouth, tongue, and throat Found inside of papillae (elevations on tongue) Pathway: Chemicals dissolve in saliva enters taste pore gustatory hair gustatory receptor cell taste bud facial, glossopharyngeal, & vagus nerves medulla hypothalamus thalamus cerebral cortex Hearing & Equilibrium Uses the ear 2 types of equilibrium Static: maintenance of body position Dynamic: correction of body position Both use the crista (hair cells) in the ear The Ear 3 main regions External ear: collects sound waves Auricle (pinna) : made of cartilage External auditory canal: connects auricle with eardrum; hairs and cerumen for protection Tympanic membrane (ear drum): thin partition between outer and inner ear; resonates with sound waves The Ear continued Middle ear: air-filled cavity between ear drum and internal ear Ossicles located here Malleus, incus, stapes Internal ear Outer bony labyrinth Cochlea (H), vestibule (E), semicircular canals (E), perilymph fluid Inner membranous labyrinth Series of sacs & tubules Endolymph fluid A look at the ear Sound Pathway Auricle eardrum malleus incus stapes oval window perilymph vestibule endolymph cochlea vestibulocochlear nerve medulla Soundwaves are the stimuli that we perceive as sound Healthy human ear hears 20-20,000 Hertz (Hz) in pitch (frequency) 0-90 decibels (dB) in intensity (loudness) Ear disorders Otitis externa: outer ear infection a/k/a swimmer’s ear Otitis media: middle ear infection; results when bacteria from throat creeps up Eustachian (auditory) tube and into ears