© 2009 Delmar, Cengage Learning Chapter 10 Special Senses
Dec 16, 2015
© 2009 Delmar, Cengage Learning
Sensory Receptors
• Stimulated by changes in the environment
• Generalized in body– Touch, pain, temperature and pressure (proprioceptors)
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Sensory Receptors
• Specific receptors– Taste buds of the tongue
– In the nose
– In the retina of the eye
– In the inner ear (organ of Corti)
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The Eye
• Tender sphere about 1 inch (2.5 cm) in diameter
• Protected by orbital socket, eyebrows, eyelids, and eyelashes
• Lacrimal duct and glands
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The Eye
• Oil glands
• Conjunctiva
• Stereoscopic vision
• The wall of the eye has three layers– Sclera
– Choroid
– Retina
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Sclera
• Outer layer of the eye which is the white of the eye
• Fibrous capsule maintains shape and protects
• Extrinsic muscles
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Extrinsic Muscles
• Superior rectus
• Inferior rectus
• Lateral rectus
• Medial rectus
• Superior rectus
• Inferior oblique
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Cornea
• Circular clear area in front center of the sclerotic coat
• Transparency allows passage of light rays
• Five layers
• Very sensitive to pain and touch
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Choroid Coat and the Iris
• Middle layer of the eye
• Blood vessels to nourish the eye
• Nonreflective pigment rendering it dark and
opaque
• Circular opening called the pupil
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Choroid Coat and the Iris
• Muscular layer surround the pupil called the
iris
• Color of iris depends on the number and size of melanin pigment
• Intrinsic muscles– Sphincter papillae (constricts pupil)
– Dilator papillae (dilates pupil)
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Lens and Related Structures
• Lens– Crystalline structure located behind the iris and pupil
• Ciliary body
• Anterior chamber– Aqueous humor
• Posterior chamber– Vitreous humor
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Retina
• Innermost, or third coat of the eye
• Images focus on the retina
• Optic nerve
• Cerebral cortex (occipital lobe)
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Retina
• Rods and cones
• Macula lutea and fovea centralis
• Optic nerve or blind spot
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Pathway of Vision
• Images in the light
• Cornea
• Pupil
• Lens
• Retina
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Pathway of Vision
• Rods and cones
• Optic nerve
• Optic chiasma
• Optic tracts
• Occipital lobe of the brain for interpretation
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Eye Disorders
• Conjunctivitis
• Glaucoma
• Cataracts
• Macular degeneration
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Eye Disorders
• Detached retina
• Diabetic retinopathy
• Sty (hordeolum)
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Eye Surgery
• Cataract surgery– Phacoemulsification
– Extracapsular extraction
• Detached retina surgery– Laser surgery and cryotherapy
– Pneumatic retinopexy
– Vitrectomy
– Scleral buckle
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Eye Surgery
• Visual defects
• LASIK (laser-assisted in-situ keratomileusis)
• PRK (photorefractive keratectomy)
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Eye Injuries
• Simple eye irritation
• Corneal abrasions and scarring
• Chemical or fragment eye irritations
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Eyestrain
• Signs and symptoms
• Most common cause is a computer
• Dry eyes can also cause eyestrain
• Prevention
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Vision Defects
• Night blindness
• Color blindness
• Presbyopia
• Hyperopia
• Myopia
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Effects of Aging – Eye
• Decreased ability to focus on fine detail
• Compromised accommodation
• Slower to adjust to changing light conditions
• Peripheral vision and depth perception decline
• Loss of visual acuity
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The Ear
• Picks up sound waves and sends these impulses to the auditory center of the brain
• Auditory center in temporal area just above ears
• Receptor for hearing– Organ of Corti
• Involved in equilibrium
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Middle Ear
• Connects to pharynx (throat) via eustachian tube
• Hammer (malleus)
• Anvil (incus)
• Stirrup (stapes)
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Inner Ear
• Cochlea
• Cochlear duct
• Organ of Corti
• Three semicircular canals
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Pathway of Hearing
• Sound waves
• Pinna
• Auditory canal
• Tympanic membrane
• Ear ossicles
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Pathway of Hearing
• Cochlea receptors
• Cochlear nerve
• Temporal lobe of the brain for interpretation
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Pathway of Equilibrium
• Movement of head
• Stimulates equilibrium receptors in the semicircular and vestibule areas of the inner
ear
• Vestibular nerve
• Cerebellum of the brain for interpretation
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Loud Noise and Hearing Loss
• Hearing is both sensitive and fragile
• Damage done by loud noises
• Sound measured in decibels
• Prevention of damage
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Ear Disorders
• Otitis media
• Otosclerosis
• Tinnitus
• Presbycusis
• Meniere’s disease
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Types of Hearing Loss
• Conductive hearing loss
• Sensorineural damage
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Effects of Aging – Hearing
• Tympanic membrane becomes fibrous
• Degeneration of ear bones, vestibular structure, cochlea, and organ of Corti
• Loss of hearing high-pitched frequencies
• Diminished ability to hear consonants
• Speech of others sounds garbled
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Hearing Aids
• Behind the ear (BTE)
• In the ear (ITE)
• Canal aids
• Body aids
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The Nose
• Smell accounts for about 90% of what we think of as taste
• Warms and moistens air breathed in
• Receptors– Olfactory epithelium and bulbs
• Olfactory nerve
• Limbic system, thalamus, and frontal cortex
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Disorders of the Nose
• Rhinitis
• Nasal polyps
• Deviated nasal septum
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Effects of Aging – Smell
• Decreased in the number of olfactory neurons
• Decreased sense of smell affects appetite, social relationships, and detection of warning smells
• Senile rhinitis
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The Tongue
• Tongue is a mass of muscle tissue
• Papillae
• Taste buds for sweet, sour, salty, and bitter
• Receptors in the taste buds send stimuli through three cranial nerves to the cerebral cortex for interpretation
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Effects of Aging – Tasting
• Decrease in taste buds
• Increased amounts of salt, sweet, sour, and bitter needed to identify the food
• Impact of full upper dentures