26 The Special Senses Lesson 2: The Senses of Hearing, Taste and Smell

Lesson Objectives Upon completion of this lesson, students should be able to … Define and spell the terms to learn for this chapter. Describe the anatomy of the ear and briefly explain the function of each structure. Explain common disorders associated with the ear.

Lesson Objectives Describe the anatomy of the nose and explain how the sense of smell occurs. Identify the anatomical structures that make up the special senses. Discuss the sense of taste, and briefly explain the function of taste buds.

Anatomy of the Ear 4

Three Main Divisions of the Ear External ear Middle ear Inner ear 5

Structure and Function of the External Ear Pinna, or auricle: Funnels sound waves through the auditory canal to the tympanic membrane Auditory canal, or auditory meatus: S-shaped, secretes cerumen or earwax Tympanic membrane, or eardrum: Separates the external ear from the middle ear Fundus: Floor of the tympanic cavity

Structure and Function of the Middle Ear Tiny cavity in temporal bone of skull Contains three small bones: malleus (hammer), incus (anvil), stapes (stirrup) Function of middle ear Transmits sound vibrations Equalizes air pressure on both sides of the tympanic membrane Protects the ear from damaging noise Sound vibrations are transmitted by ossicles from the tympanic membrane to the oval window and into the inner ear

Structure and Function of the Inner Ear Bony labyrinth in the temporal bone made of: Cochlea, vestibule, and three semicircular canals Bony and membranous labyrinths separated by perilymph Tiny hair cells function as receptors for hearing and balance Cochlea resembles a snail’s shell Three tubelike channels run the length of the spiraling shell Cochlear duct runs between the upper and lower chambers

Structure and Function of the Inner Ear Fundus of the internal auditory meatus is known as the vestibule Vestibular nerve divides the acoustic or eighth cranial nerve Organ of Corti contains nerve endings that transmit sound vibrations received from the stapes to the auditory region of the brain via the eighth cranial nerve Eustachian tube extends from the middle ear 3-4 cm to the nasopharynx

Path of Sound Vibrations 10

Two Most Common Types of Hearing Disorders Conductive: Temporary – sound is not conducted efficiently through the auditory canal to the eardrum and the middle ear Hearing loss can be corrected Sensorineural: Permanent – caused by damaged cochlea or nerve pathways from the inner ear to the brain Hearing loss cannot be corrected

Common Disorders of the Outer Ear

Impacted Cerumen Cerumen is produced by the sebaceous glands as lubrication Impacted cerumen obstructs the auditory canal Affects older adults Exacerbated by cotton-tipped swab use Signs and symptoms include: Blocked or muffled hearing, plugged feeling in the ear, pain Treatment includes: Softening wax then flushing with a syringe. If left untreated, impacted cerumen leads to tinnitus

Ruptured Tympanic Membrane Caused by objects or unequal air pressure on both sides of membrane Signs and symptoms: Sharp, sudden pain followed by drainage of fluid Tinnitus Treatment includes: Antibiotics, analgesics, flushing with warm earwax softeners or saline solution

Common Disorders Associated with the Middle Ear

Otitis Inflammation of any part of the ear Otitis externa (swimmer’s ear) – inflammation of the outer ear Otitis media – inflammation of the middle ear

Otitis Media Signs and symptoms include: Treatment includes: Tugging on the ear, irritability or fussiness, fever and fluid drainage, difficulty sleeping, a loss of balance Treatment includes: Eliminating the cause of infection with oral antibiotics and decongestants, tubal insufflation every 1 to 2 days

Otosclerosis Hereditary condition Tissue surrounding the stapes grows abnormally Prevents the stapes from transmitting sound vibrations Signs and symptoms include: Hearing loss in one or both ears, tinnitus, dizziness Treatment includes: Use of a hearing aid or surgery

Common Disorders Associated with the Inner Ear

Tinnitus Causes include: Signs and symptoms include: There is no cure Hearing loss, loud noise, certain medications, allergies, tumors Signs and symptoms include: Ringing or roaring in one or both ears There is no cure Some relief is provided with the use of hearing aids, maskers, and medications such as antiarrhythmics and antidepressants

Ménière’s Disease Caused by changes in fluid volume in the inner ear Signs and symptoms include: Vertigo, tinnitus, headache, nausea, vomiting, diarrhea, hearing loss, pressure, or pain Treatment includes: Low-salt diet, avoiding caffeine and alcohol, diuretic drugs may be administered, eliminating tobacco use, reduce stress levels

Presbycusis A gradual deterioration of sensory receptors in the cochlea Caused by loud noises, infection, injury, and side effects of medications Occurs in both ears and affects normal and high-pitched tones Treatment typically involves the use of a hearing aid

How the Sense of Taste and Smell Function Together Olfactory cells respond to changes in chemical concentrations activating smell receptors Receptors send information to the brain via olfactory nerves Molecules move from the nose to the mouth region stimulating taste buds

Four Types of Taste Cells Sweet, located on tip Sour, on sides Salty, on tip and sides Bitter, at back

The Sense of Touch Oldest, most primitive sense First sense humans experience in the womb and the last one lost before death Found over the entire body Originates in the dermis Nerve endings in the dermis called receptors transmit information to the brain via the spinal chord More nerve endings equals more sensitivity

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