Ch 2: Anatomy and Physiology

Question 1

What are the two parts of the external ear? What is the function of the external ear?

Answer 1

• The auricle (or pinna) and the external auditory canal.

- The functions of the external ear are twofold: collect and funnel sound waves, and protect the eardrum.

Question 2

What are some of the problems that can occur in the external ear? 3

Answer 2

Problems in the external ear include these:
• impacted wax
• skin disorders, like dermatitis
• stenosis – narrowing due to infection or injury

Question 3

What does the sound-conducting mechanism of the middle ear consist of?
How does this sound-conducting mechanism work?

Answer 3

a. The sound-conducting mechanism consists of the eardrum, the ossicles (malleus, incus, and stapes), ligaments, and two muscles (the tensor tympani and the stapedial muscle).
b. The eardrum is sensitive to minute sound pressure disturbances that cause the eardrum to vibrate.
- The vibration motion of the eardrum is transferred across the ossicles to the oval window and thus from the outer ear canal to the inner ear.
- Sound energy in air is transformed to mechanical energy in the middle ear.
- The middle ear conducts sound energy from the outer ear to the inner ear. When sound waves strike the eardrum, the ossicles begin to vibrate and the stirrup vibrates the oval window on proportion the the frequency and intensity of the sound. As the sound is transferred through the middle ear it is amplified. This is because of the size difference between the oval window and the eardrum (because the oval window is smaller, the ossicles acts as mechanical transformers and levers that increase the sound energy amplifying the sound waves transmitted to the inner ear). The result is an increase in sound energy by about 20 times the original.

Question 4

What happens to the sound energy as it is transmitted from the outer ear to the inner ear?

Answer 4

As sound is transmitted, it is amplified by these mechanisms:

a. the eardrum (where vibrations enter the middle ear), which is much larger than the oval window (where the vibrations exit the middle ear)
b. the ossicles, which act as levers increasing the sound energy
- Because of these two mechanisms, sound is amplified by 20 times the original volume.

Question 5

What are some common middle-ear disorders? 3-4

Answer 5

Common middle ear disorders include:

• infection
• otosclerosis (abnormal bone growth of middle ear)
• perforated eardrum, and a break of the ossicles.

Question 6

What structures make up the inner ear? 2+3

Answer 6

• The inner ear is also called the labyrinth which is made up of two main parts: the bony labyrinth and the membranous labyrinth.
• The semicircular canals, cochlea, and vestibule make up the bony labyrinth (is filled with a fluid called perilymph).
• The membranous labyrinth is within the bony labyrinth and consists of the balance organs and cochlear duct (is filled with a fluid called endolymph).

Question 7

What are two functions of the inner ear?

Answer 7

The two functions of the inner ear are maintaining balance and hearing.

Question 8

How does the inner ear transfer sound energy?

Answer 8

• At the oval window, fluid conduction of sound energy begins. Vibration of the oval window causes vibration of the perilymph; this vibration is transferred to the endolymph within the cochlear duct.
• The membranous cochlear duct contains the receptors, or hair cells, that are attached to nerve endings.
• When the fluid vibrates, the hair cells stimulate the nerve endings that send electrical impulses to the brain.
• When sound is transmitted through to the oval window, the ossicular movement causes vibrations in the fluids of the cochlea. The vibrating fluid, in turn, causes the tiny hair cells to vibrate. The sound pressure is then converted to neural, or electrical, energy that is transmitted to the brain.

Question 9

• Where in the cochlea are high frequencies detected?

- Where are lower frequencies detected?

Answer 9

• High frequencies are detected by the hair cells that are close to the oval window (base of the cochlea).
• Hair cells further from the oval window detect lower frequency sounds.
• The lowest frequency sounds are detected at the apex of the cochlea (the point furthest from the oval window).

Question 10

• What type of hearing loss is generally caused by problems in the external ear and middle ear?
• What type of hearing loss is caused by problems in the inner ear?

Answer 10

Problems in the external or middle ear cause conductive hearing loss.
-Problems in the inner ear cause sensorineural hearing loss.

Question 11

What are the most common causes of sensorineural hearing loss in adults?

Answer 11

Aging and noise are the most common causes of sensorineural hearing loss in adults.