Topic Two - The Outer Ear

Question 1

Correctly label a diagram of the outer ear and its landmarks

Answer 1

See Kahoot/Quizlet Quiz
https://quizlet.com/226487433/pinna-anatomy-diagram/

Question 2

What is the function of cerumen?**

Answer 2

Cleaning
- “Conveyer belt” of epithelial migration, aided by jaw movement, moves the cerumen outward taking with is any dirt, dust and particle matter

Lubrication
- Prevents desiccation and itching of the skin

Antibacterial and antifungal
- Provides some protection against some bacteria and inhibits the growth of some fungi

Question 3

How is cerumen produced?**

Answer 3

Within the cartilaginous portion of the ear canal are the following structures responsible for the production of cerumen:

• Modified apocrine sweat glands
• Sebaceous glands
• Pilosebaceous units
• Vibrissas (hair)

These glands produce secretions that mix to form cerumen

Question 4

What regions are included in the outer ear?

Answer 4

• The pinna
• External auditory meatus
• Tympanic membrane

Question 5

What nerves are responsible for the innervation of the outer ear muscles?

Answer 5

• Superior
• Anterior
• Posterior auricular muscles are innervated by the post-auricular branch of the facial nerve

Question 6

What are the two reflexes involving the outer ear muscles?

Answer 6

• Preyer reflex (guinnea pig reflex)
• Post-auricular muscle response (PAMR)

Question 7

What are the main functions of the pinna?

Answer 7

1. Collect and direct the sound waves to the tympanic membrane
2. Helps with directional hearing

Question 8

How do humans distinguish between left/right sounds?

Answer 8

Interaural timing difference
- The sound will reach the ear facing the sound source slightly before it reaches the other ear

Interaural Level difference
- The sounds in the ear facing the sound source are more intense than the other ear due to weakening of the wave as it passes over the head.

• The pinna is not necessary for left/right sound source distinguishing.

Question 9

How do humans distinguish between up/down and forward/back sounds?**

Answer 9

Because there is no interaural time or level difference, the ridges on the pinna help to distinguish between front/back and up/down sounds by:

• Constructive or destructive interference
• This awareness is developed during childhood

Question 10

How long is the ear canal?

Answer 10

Around 2.5cm

Question 11

How is the ear canal divided?

Answer 11

• Lateral cartilaginous one-third
• Medial bony two-thirds

Question 12

What is the main resonant frequency of the ear canal for males and what does that mean?

Answer 12

Resonance occurs in a tube, such as the ear canal, due to the bounce back of sound which increases and decreases certain sounds

The main resonant frequency for males is 2.5 kHz

This means that 2.5kHz sounds get boosted

Question 13

What innervates the outer ear and tympanic membrane?

Answer 13

Auriculotemporal nerve - superficial branch of the mandibular part of the trigeminal nerve

Question 14

What innervates the ear canal?

Answer 14

Cranial nerves:
- V (trigeminal)
- VII (facial)
- IX (glossopharyngeal)
- X (vagus)

Question 15

Why does the tympanic membrane need to be strong?

Answer 15

• Convey sound
• Resist pressure changes

Question 16

What is the tympanic membrane composed of?**

Answer 16

The tympanic membrane is a cone shaped structure, 0.1mm thick, 10mm wide composed of 3 layers:

• Epidermal layer
• Lamina propria: A fibrous layer called the ‘pars tensa’ (the tense part). Extends everywhere except the ‘pars flaccida’/Shrapnell’s membrane
• Mucosal layer

Question 17

What are the four quadrants of the tympanic membrane?

Answer 17

See Kahoot quiz