1. 26
The Special Senses
Lesson 2:
The Senses of Hearing, Taste and Smell

2. 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.

3. 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.

4. Anatomy of the Ear 4

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

6. 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

7. 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

8. 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

9. 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

10. Path of Sound Vibrations10

11. 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

12. Common Disorders of the Outer Ear

13. 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

14. 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

15. Common Disorders Associated with the Middle Ear

16. 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

17. 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

18. 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

19. Common Disorders Associated with the Inner Ear

20. 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

21. 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

22. 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

23. 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

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

25. 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

26. Questions? 26