Download - 12 sense organs
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Chapter 12Somatic and Special Senses
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Receptor Types
Chemoreceptors• respond to changes in chemical concentrations
Pain receptors• respond to tissue damage
Thermoreceptors• respond to changes in temperature
Mechanoreceptors• respond to mechanical forces
Photoreceptors• respond to light
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Sensory Adaptation
• adjustment of sensory receptors from continuous stimulation• stronger stimulus required to activate receptors• smell receptors undergo sensory adaptation
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Touch and Pressure Senses
Free nerve endings• common in epithelial tissues• detect touch and pressure
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Touch and Pressure Senses
Meissner’s corpuscles
• abundant in hairless portions of skin
• detect light touch
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Touch and Pressure Senses
Pacinian corpuscles
• common in deeper subcutaneous tissues, tendons, and ligaments• detect heavy pressure
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Temperature Senses
Warm receptors• sensitive to temperatures above 25oC (77o F)• unresponsive to temperature above 45oC (113oF)
Cold receptors• sensitive to temperature between 10oC (50oF) and 20oC (68oF)
Pain receptors• respond to temperatures below 10oC• respond to temperatures above 45oC
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Sense of Pain
• free nerve endings • widely distributed • nervous tissue of brain lacks pain receptors• stimulated by tissue damage, chemical, mechanical forces, or extremes in temperature
•Phantom Pain
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Referred Pain
• may occur due to sensory impulses from two regions following a common nerve pathway to brain
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Special Senses
• smell in olfactory organs•# 1
• taste in taste buds•# 7,9 &10
• hearing and equilibrium in ears•# 8
• sight in eyes•# 2 (vision)•# 3,4 & 6 (movement)
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Olfactory Receptors
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Smell
Olfactory Receptors• chemoreceptors• respond to chemicals dissolved in liquids
Olfactory Organs• contain olfactory receptors and supporting epithelial cells• cover parts of nasal cavity, superior nasal conchae, and a portion of the nasal septum
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Taste
Taste Buds• organs of taste• located on papillae of tongue, roof of mouth, linings of cheeks and walls of pharynx
Taste Receptors• chemoreceptors• taste cells – modified epithelial cells that function as receptors• taste hairs –microvilli that protrude from taste cells; sensitive parts of taste cells
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Taste Receptors
Cranial nerves 7, 9 & 10
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Taste Sensations
Four Primary Taste Sensations• sweet – stimulated by carbohydrates• sour – stimulated by acids• salty – stimulated by salts• bitter – stimulated by many organic compound
Spicy foods activate pain receptors
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Hearing
Ear – organ of hearing
3 Sections• External• Middle• Inner
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External Ear
• pinna• collects sounds waves
• outer ear canal• aka ear canal• carries sound to tympanic membrane
• eardrum • aka ear tympanic membrane• vibrates in response to sound waves
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Middle Ear
• auditory ossicles• vibrate in response to tympanic membrane• malleus, incus, and stapes• aka hammer, anvil & stirrup
• oval window • stapes (stirrup) vibrates against it to move fluids in inner ear
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Auditory Tube
• eustachian tube • connects middle ear to throat• helps maintain equal pressure on both sides of tympanic membrane• usually closed by valve-like flaps in throat
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Inner Ear
• complex system of labyrinths• osseous labyrinth
• bony canal in temporal bone• filled with perilymph
• membranous labyrinth• tube within osseous labyrinth• filled with endolymph
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Inner Ear
Parts of Inner Ear• cochlea
• functions in hearing• snail-shaped• Have hearing receptor cells (hair cells) that bend with different frequencies to generate a nerve impulse
• semicircular canals• functions in equilibrium• fluid-filled
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Semicircular Canals
• balance •three canals at right angles• rapid turns of head or body stimulate hair cells
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Sight
Visual Accessory Organs• eyelids• lacrimal apparatus• extrinsic eye muscles
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Eyelid
• composed of four layers• skin• muscle • connective tissue• conjunctiva
• orbicularis oculi - closes• levator palpebrae superioris – opens• tarsal glands – secrete oil onto eyelashes; so lids don’t stick• conjunctiva – mucous membrane; lines eyelid and covers portion of eyeball
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Lacrimal Apparatus
• lacrimal gland• lateral to eye• secretes tears
• canaliculi• collect tears
• lacrimal sac• collects from canaliculi
• nasolacrimal duct• collects from lacrimal sac• empties tears into nasal cavity
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Extrinsic Eye Muscles
Superior rectus• rotates eye up and medially
Inferior rectus• rotates eye down and medially
Medial rectus• rotates eye medially
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Extrinsic Eye Muscles
Lateral rectus• rotates eye laterally• *Abducens Nerve VI
Superior oblique• rotates eye down and laterally• * Trochlear Nerve IV
Inferior oblique• rotates eye up and laterally
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Outer Eye
Cornea• anterior portion• transparent• light transmission• light refraction
Sclera• posterior portion• white of eye• protection
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Middle Tunic
Ciliary body• holds lens• moves lens for focusing
Choroid coat• provides blood supply• pigments absorb extra light
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Lens
• transparent• biconvex• lies behind iris• elastic!!!• held in place by suspensory ligaments
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Accommodation• changing of lens shape to view objects
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Iris
• composed of connective tissue and smooth muscle• pupil is hole in iris• dim light stimulates radial muscles and pupil dilates• bright light stimulates circular muscles and pupil constricts
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Anterior Portion of Eye
• filled with aqueous humor• maintains shape of anterior portion of eye
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Inner Eye
• retina•contains photoreceptors•continuous with optic nerve•rods provide vision in dim light•cones provide color vision
• optic disc – blind spot; contains no visual receptors; index card trick
• vitreous humor – thick gel that holds retina flat against the back of the eye; gives eye round shape
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Layers of Retina
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Focusing On Retina• as light enters eye, it is refracted by
• convex surface of cornea• convex surface of lens
• image focused on retina is upside down and reversed from left to right
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Clinical Application
Refraction Disorders
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Visual Pathway
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Snellen Chart
• What does 20/40 or 20/100 mean?
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Astigmatism
Due to irregular shaped cornea
Or
Irregular curvature of the lens
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Colorblindness
• Sex-linked trait; usually in males
• Varying degrees of colorblindness
• Tests
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Corneal transplants
• Cornea disease is the leading cause of blindness
• Restore sight with a transplant
• Central 2/3 of the cornea are replaced
• Heals well; usually not rejected