Copyright ©2012 Delmar, Cengage Learning. All rights reserved. Chapter 25 The Senses.
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Transcript of Copyright ©2012 Delmar, Cengage Learning. All rights reserved. Chapter 25 The Senses.
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Copyright ©2012 Delmar, Cengage Learning. All rights reserved.
Chapter 25
The Senses
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The Senses of the Human Bodyand Corresponding Organs
• Sight: the eye• Hearing: the ear• Taste: the tongue• Smell: the nose• Touch: the skin
• Knowledge of the environment requires sensory organs, cranial nerves, and the brain to interpret stimuli.
Copyright ©2012 Delmar, Cengage Learning. All rights reserved.
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Copyright ©2012 Delmar, Cengage Learning. All rights reserved.
The Structures of the Eye
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The Structures of the Eye
• Sclera: tough outer covering – Maintains the shape of the eye
• Extraocular muscles (6)– Contract or relax to permit movement of the eyeball
• Choroid– Layer under the sclera– Contains the blood vessels that serve the eye tissues– This layer also has a nonreflective pigment that keeps
light from reflecting within the eye.
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The Structures of the Eye
• Retina: focuses an image onto the surface• Iris: colored circular muscle that surrounds the
pupil; regulates the amount of light• Optic disk: blind spot • Pupil: central opening• Cornea: curved covering of the sclera that can
correct some unclear images
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The Structures of the Eye
• Conjunctiva: the white of the eye• Vitreous humor: thick, jellylike substance that
maintains the shape of the eyeball• Aqueous humor: salty clear fluid; circulates
between the chambers
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The Structures of the Eye
• Fovea centralis: posterior surface of the retina; the area of sharpest vision
• Rods: nerve cells that transmit the stimuli so we can see in black and white
• Cones: nerve cells that transmit the stimuli so we can see in color
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The Effects of the Lens and Corneaon Focusing Images
• When the lens or cornea has an abnormal curvature, the image is improperly refracted.
• When the image is focused in front of the retina, the person is said to nearsighted.
• The medical term for nearsightedness is myopia.
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The Effects of the Lens and Corneaon Focusing Images
• When the image is focused behind the retina, the person is said to be farsighted.
• The medical term for farsightedness is hyperopia.
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Age-Related Macular Degeneration
• A disease that affects the most sensitive part of the retina, and alters the center of the visual field
• Results in a gradual loss of central vision, but side vision is maintained
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Amblyopia
• Also called lazy eye• Most often affects children under age 5• One eye turns inward, causing blurred vision
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Arcus Senilis
• Accompanies normal aging • Results in a thin greyish-white arc or circle not
quite at the edge of the cornea
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Blepharitis
• Inflammation of the edges of the eyelids involving the hair follicle and glands
• Results in itching and burning, rubbing eyes, and constant blinking
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Cataract
• Gradually developing opacity of the lens• Occurs most frequently in persons over the age of
70• Causes painless, gradual blurring and loss of vision
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Conjunctivitis
• Caused by inflammation of the conjunctiva• Begins in one eye and spreads to the other;
causes redness and a “bloodshot” appearance• Usually caused by a bacterial infection
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Corneal Abrasion
• A scratch or trauma to the cornea usually caused by a foreign body in the eye
• Vision can be affected if the location and extent of the injury are significant
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Diabetic Retinopathy
• Usually results from juvenile or adult diabetes• Edema of the retina causes light to scatter• Capillary walls dilate, twist, and/or
hemorrhage• Causes glare, blurred vision, and reduced
visual acuity
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• Characterized by excessive intraocular pressure that results in atrophy of the optic nerve; causes severe visual impairment and eventual blindness
Glaucoma
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Diseases of the Eye• Closed-angle glaucoma
– Aqueous humor cannot drain because of a blockage and pressure rises slowly
• Acute closed-angle glaucoma– Obstruction of the drainage holes resulting from
automatically shallow chambers and a thickened iris that closes the passages
– There is a rapid onset of symptoms; this is considered an emergency.
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Hordeolum and Iritis
• Hordeolum– Localized infection of the gland of the eyelid;
produces an abscess around an eyelash– Causes red, painful, and swollen eyes
• Iritis– Inflammation of the iris; causes moderate to
severe eye pain, sensitivity to light, and small, nonreactive pupils
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Presbyopia and Ptosis• Presbyopia
– Inability of the lens to accommodate for near vision; usually occurs as a normal part of the aging process
• Ptosis– Drooping of the upper eyelid that results in the
eyes appearing to be only partially open– Could be the result of a congenital condition,
aging, excess fatty folds, or neurological factors
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Retinal Detachment
• Results from separation of the retina from the choroid layer of the eyeball
• Causes the patient to see floating spots, flashes of light, and a gradual loss of vision
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Strabismus
• One eye deviates with the gaze being abnormally inward or outward or higher or lower than the other eye
• This can results in:– Esotropia: abnormally inward gaze– Exotropia: abnormally outward gaze
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The Structures of the Ear
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The Structures of the Ear
• Pinna: external ear shell; also called the auricle; collects and directs sound down the external auditory canal
• External auditory canal: passageway from outside to the eardrum
• Tympanic membrane: eardrum; vibrates when sound waves hit it
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The Structures of the Ear
• Vibrations from the tympanic membrane hit the three small bones of the middle ear.
• The malleus (hammer) strikes the incus (anvil), which moves the stapes (stirrups).
• This communicates the vibrations to the inner ear when the stapes pushes against the fluid in the vestibule of the inner ear.
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The Structures of the Ear
• The middle ear is connected by the eustachian tube to the throat.
• The eustachian tube equalizes the air pressure in the middle ear with the outside air pressure.
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The Structures of the Ear
• Vibrations from the middle ear continue through a snail-shaped organ called the cochlea.
• The cochlea contains a collection of specialized nerve cells called the organ of Corti.
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The Structures of the Ear
• The organ of Corti transmits impulses to the auditory nerve, which passes them on to the auditory center of the temporal lobe of the cerebrum of the brain for interpretation.
• The inner ear also contains three semicircular canals that are responsible for maintaining balance.
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The Balance Function of the Inner Ear
• Hairlike nerve cells within the three canals are embedded in a gelatin-like material that pushes against receptors when the head moves and transmits this change in position to the brain.
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Auditory canal obstruction
• Anything in the ear canal that can occlude the opening
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Hearing Loss
• Reduced ability to perceive sound at normal levels
• Hearing loss can be the result of obstruction, nerve damage from prolonged exposure to noise, or disease
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Meniere’s Disease
• Disorder of the inner ear that usually affects only one ear; typically begins between ages 20 and 50
• Results in extreme dizziness (vertigo) and ringing in the ears (tinnitus).
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Motion Sickness
• Loss of balance, perspiration, headache, nausea, and vomiting brought on by irregular motion
• Examples: riding in cars, boats, planes, or amusement park rides
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Otitis
• Otitis externa– Infection of the external auditory canal that
causes pain and hearing loss• Otitis media
– Infection of the middle ear often associated with respiratory infections
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Otosclerosis and Prebycusis
• Otosclerosis– Loss of movement of the stapes that results in
deafness called bone conduction deafness• Presbycusis
– Progressive hearing loss that usually results as a result of aging
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Epistaxis and Nasal Polyps
• Epistaxis– Bleeding from the nose that can result from
trauma or a disease process• Nasal polyps
– Benign growths inside the nose that obstruct the airway
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Rhinitis
• A reaction to airborne allergens that results in sneezing, watery eyes, and itching of the eyes and nose
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The Structures of the Nose
• The sense of smell is caused by the olfactory organ in the top of the nasal cavity.
• Nerve fibers in the nose respond to stimuli and these nerve fibers run through tiny holes in the skull to the olfactory center in the brain.
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The Structures of the Tongue
• The ability to taste flavors is located in the receptors of the taste buds on the tongue.
• These receptors are located at the tip, sides, and back of the tongue.
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Taste Sensation and the Corresponding Areas of the Tongue
• Tip– Sweet
• Sides– Sour
• Back– Bitter
• Area between tip and sides– Salty
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Candidiasis
• Fungal infection of the mouth and throat that results in white patches that appear on the tongue, mouth, or throat
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Glossitis and Oral Cancer
• Glossitis– Inflammation of the tongue
• Oral cancer– Cancer of the tongue, mouth, or throat; often
linked to tobacco use
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The Structures of the Skin
• Touch receptors are located in the fingertips.• Pain receptors are bare nerve endings in the
skin and other organs.• Skin receptors perceive heat and cold.
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The Skin’s Contact Receptors
• The sense of touch involves pressure or traction that activates mechanoreceptors.
• Radiant energy, heat or cold, activates thermoreceptors.