Module 1 Lesson 3 - 2

Structure of the Ear: Outer Ear

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Read pages 419 - 420

The ear has three major regions: the outer ear, the middle ear, and the inner ear. The most obvious structure of the outer ear is the pinna (plural: pinnae). Some animals can move their pinnae to maximize trapping sound waves. By moving its pinnae, the fennel fox can pinpoint with great accuracy the direction from which a sound originates. For many animals, survival often is dependent on early detection of sound.

In humans, the muscles of the pinna are vestigial, or non-functional, and we cannot move our pinnae. However, people sometimes cup an ear with a hand to simulate an enlarged pinna to hear better by collecting and directing more sound waves. Do you know anyone who can move their pinnae slightly?

     

The sound waves collected by the pinna are directed down the auditory canal to the tympanic membrane (or eardrum).

Ear wax is produced in the auditory canal to moisten the passage and tympanic membrane for flexibility. It collects and channels out debris, too. Sometimes, ear wax can accumulate in the auditory canal and cause conductive deafness. To remove the ear wax, a syringe with warm water is used to float out ear wax.

The auditory canal ends at the tympanum, also known as the tympanic membrane, or more commonly the eardrum. The sound waves cause it to vibrate, which converts sound energy to mechanical energy.

The middle ear extends from the tympanum, or tympanic membrane, to the oval window. The tympanic membrane is connected to the ossicles (malleus, incus, and stapes ). The ossicles of the middle ear are specialized to conduct and amplify the mechanical vibrations on the oval window.

Note: You need not memorize the names of the three ossicles for the Biology 30 course.

What structures constitute the middle ear? Be careful here. The diagram seems to show that the semicircular canals are part of the middle ear. This is not so! The middle ear is bordered by the tympanum and the oval window.

When you have a cold and are suffering from a throat infection, your throat infection can develop quickly into a terrible ear ache. You might think your ear drum will burst from the pressure building in the middle ear, but in most cases it does not. In some serious cases, ear infections can cause the eardrum to rupture, which can result in partial hearing loss.

Middle ear infections are common because microorganisms, such as bacteria and viruses, can reach the middle ear by entering at the nose and at the mouth to make their way eventually to the Eustachian tube by way of the throat. The Eustachian tube connects the middle ear to the throat.

Have you ever noticed your ears "pop"? Your eardrum "popping" indicates the pressures equalizing on each side of the eardrum. This is common when you are in an unpressurized airplane, under water, or travelling in the mountains. The Eustachian tube equalizes air pressure in the middle ear, such as during a rise in altitude in mountain hiking or riding in airplanes. Yawning, chewing, or swallowing can help equalize the pressure.

Self-Check

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To help you understand and apply the concepts that are studied with the outer and middle ear, complete the following questions.

1. Describe how your hearing would be affected if you poked a hole in your tympanum while trying to remove ear wax.
2. During take-off or landing on a plane ride, some passengers chew gum. Explain the physiological basis of this gesture.