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Chapter 18: The Senses. Chapter Objectives. Role of the sensory system. Ear and the eye; the function of each part. The pathway of nerve impulses from the ear to the brain. Roles of the retina and the optic nerve in vision. Word parts pertaining to the senses.
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Chapter Objectives • Role of the sensory system. • Ear and the eye; the function of each part. • The pathway of nerve impulses from the ear to the brain. • Roles of the retina and the optic nerve in vision. • Word parts pertaining to the senses. • Main disorders pertaining to the ear and the eye. • Abbreviations used in the study of the ear and the eye.
General Senses • Distributed throughout body • Pain • Touch • Pressure • Temperature • Proprioception
Special Senses • Located within complex sense organs • Gustation = sense of taste • Olfaction = sense of smell • Hearing • Equilibrium • Vision
The Ear • Used for both hearing and equilibrium • Divided into three parts • Outer ear • Middle ear • Inner ear
The Ear (cont’d) • Outer ear • Pinna (auricle) • External auditory canal (meatus) • Contains cerumen (earwax) • Tympanic membrane (eardrum) • Transmits sound waves to middle ear
The Ear (cont’d) • Middle ear • Houses three ossicles • Malleus (hammer) • Incus (anvil) • Stapes (stirrup) • Sound waves are transmitted from footplate of stapes • Eustachian tube • Connects middle ear to nasopharynx • Equalizes pressure between outer and middle ear
The Ear (cont’d) • Inner ear • Complex labyrinth shape • Filled with fluid • Contains cochlea • Organ of Corti
The Ear (cont’d) Inner ear (cont’d) • Vestibular apparatus • Sense of equilibrium • Semicircular canals • Vestibulocochlear nerve • Cochlear branch transmits hearing impulses • Vestibular branch transmits equilibrium impulses
Hearing Loss • Sensorineural hearing loss • Damage to eighth cranial nerve or central auditory pathway • Caused by: heredity, toxins, exposure to loud noises, aging process • Treatment: cochlear implant
Hearing Loss (cont’d) • Conductive hearing loss • Results from blockage in sound transmission to inner ear • Causes: obstruction, severe infection, fixation of middle ear ossicles • Usually treated successfully
Otitis • Inflammation of the ear • Otitis media = infection leading to accumulation of fluid in middle ear • Causes • Obstruction of eustachian tube • Spreading infection • Treatment • Antibiotics • Myringotomy
Otitis (cont’d) • Otitis externa = Inflammation of external auditory canal • Also known as “swimmer’s ear” • Caused by: • Fungus • Bacterium • Common among: • People living in hot climates • Swimmers
Otosclerosis • Deterioration of bony structure of inner ear • Stapes unable to vibrate • Causes conductive hearing loss • Underlying cause unknown • Treatment • Stapedectomy • Stapes removed • Prosthetic bone inserted
Ménière Disease • Involves production and circulation of inner ear fluid • Symptoms • Vertigo (dizziness) • Hearing loss • Tinnitus (ringing in ears) • Pressure • Treatment • Drugs (to treat nausea and dizziness) • Severe cases • Inner ear or eighth cranial nerve destroyed surgically
Acoustic Neuroma • Tumor arising from neurilemma of eighth cranial nerve • Presses on surrounding nerve • Interferes with blood supply • Symptoms • Tinnitus • Dizziness • Progressive hearing loss • Other symptoms as brainstem and other cranial nerves become affected • Treatment • Surgical removal
The Eye and Vision • The eye has three layers • Sclera • Uvea • Retina
The Eye and Vision (cont’d) • Sclera • Outermost layer • Known as “White of the eye” • Extends over front of eye as transparent cornea
The Eye and Vision (cont’d) • Uvea • Middle, vascular layer • Consists of: • Choroid • Ciliary body • Muscle controls shape of lens • Allows for accommodation • Iris • Muscular ring • Controls size of pupil • Determines eye color