© 2009 Delmar, Cengage Learning Chapter 10 Special Senses.

© 2009 Delmar, Cengage Learning

Chapter 10

Special Senses

© 2009 Delmar, Cengage Learning

Special Senses

• Touch

• Vision

• Hearing

• Smell

• Taste

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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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The Eye

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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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Animation – How We See

Click Here to play Vision animation

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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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Vision Defects

• Amblyopia

• Astigmatism

• Diplopia

• Strabismus

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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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Outer Ear

• Pinna

• Canal glands

• Tympanic membrane

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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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Animation – How We Hear

Click Here to play Hearing animation

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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

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Disorders of the Tongue

• Traumatic injury

• Hairiness

• Discoloration

• Infection

• Cancer

• Burning mouth syndrome