Module 1

1. Module 1

1.36. Page 3

Lesson 6

Module 1—The Nervous System

The Middle Ear

oval window: a membrane-covered opening located between the chamber of the middle ear and the wall of the inner ear

The stapes (stirrup) is attached to it and transmits sound waves by it to the inner ear.

amplify: to increase the amplitude or the extent of a vibration; see intensity

ossicles: three tiny bones located in the middle ear that are connected to each other, to the tympanum, and to the oval window; involved in amplifying sound waves

malleus (hammer): the first in the sequence of the three ossicles located in the middle ear; connected to the tympanum and the second ossicle (incus); part of a lever system that amplifies sound waves

incus (anvil): the middle in the sequence of the three ossicles located in the middle ear; connected to the malleus and the third ossicle (stapes); part of a lever system that amplifies sound waves

stapes (stirrup): the third in the sequence of the three ossicles located in the middle ear; connected to the second ossicle (incus) and the oval window; part of a lever system that amplifies sound waves and causes vibrations in the fluid of the inner ear

The middle ear extends from the tympanum to the oval window. The structures of the middle ear are specialized to conduct and amplify the mechanical vibrations produced by sound waves. The tympanic membrane is connected to the ossicles: the malleus (hammer), incus (anvil), and stapes (stirrup).

When you have a cold and are suffering from a throat infection, your throat infection can quickly develop into a terrible earache. It may feel like your eardrum will break or burst from the pressure that is building in the middle ear. In some serious cases, ear infections can actually cause the eardrum to rupture. The rupturing and damage to the tympanic membrane can result in partial hearing loss.

The normal vibrations of the tympanic membrane cause the ossicles to act as a lever conducting and amplifying vibrations through the middle ear.

Do you remember what structures make up the middle ear? Be careful here. The diagram seems to show that the semicircularcanals are part of the middle ear. This is not so! The middle ear is bordered by the tympanum and the oval window.

An illustration of the parts of the human ear. The diagram is divided into three sections: the outer ear composed of the pinna and auditory canal; the middle ear composed of the tympanium, ossicles, oval window, and semicircular canal; and the inner ear composed of the cochlea and auditory nerve.

Inquiry into Biology (Whitby, ON: McGraw-Hill Ryerson, 2007), 420, fig. 12.20. Reproduced by permission.

Eustachian tube: a tiny passageway extending from the middle ear to the throat (pharynx); a passageway through which viruses and bacteria can travel from the nose and mouth, resulting in an inner ear infection

The Eustachian tube plays an important role in equalizing air pressure on both sides of the tympanum.

Did you notice the Eustachian tube? Taking into account the location of the Eustachian tube, can you hypothesize what events may occur as a result of a throat infection to lead to the bursting of the eardrum? When you feel your eardrum “popping,” it is an indication that the pressures on each side of the eardrum are equalizing. This is common when flying in an unpressurized plane, swimming or diving under water, or travelling in the mountains. Yawning, chewing, or swallowing can help equalize the pressures.

At this time you may wish to make summary notes, a concept organizer, or a table of structures and functions like the one below. You may also wish to prepare a labelled diagram of the ear that shows all structures and functions. Save your work in the course folder.

THE STRUCTURES AND FUNCTIONS OF THE MIDDLE EAR

Structure	Function(s)
ossicles (malleus, incus, stapes)
oval window
Eustachian tube

Self-Check

To help you understand and apply the concepts on the outer and middle ear, complete the following questions. Remember to write complete explanations in sentence form and to use correct biological vocabulary. Check your answers and file your work in your course folder. If you are unsure about an answer, consult with your teacher.

SC 7. Describe what would happen if a person poked a hole in his or her tympanum while trying to remove ear wax.

SC 8. On a plane ride where the pilot is expecting to encounter significant turbulence, the flight attendants may give hard candies to the passengers. Explain the physiological basis of this.

SC 9. Propose a hypothesis to explain why humans do not have enormous, moveable pinnae like some animals do.

SC 10. Explain why middle ear infections are common.

Check your work.

Self-Check Answers

SC 7. If the tympanum was punctured, the sound waves entering the ear through the auditory canal would not effectively be transferred to the ossicles because the tympanum would not vibrate freely in the same way as it would if it were whole and intact. Also, the sound waves would not effectively be amplified by the tympanum. Note: Answering that the person would not be able to hear as well is true, but it is not an answer with sufficient detail for Biology 30.

SC 8. Hard candies are given to encourage swallowing. Swallowing keeps the Eustachian tubes open so that pressure on the inside of the eardrum can change to accommodate any changes on the outside of the eardrum due to the turbulence.

SC 9. Humans do not have big, moveable pinnae because they depend on other senses, such as sight, to a greater extent than they do on hearing.

Humans have large cerebral lobes and have learned that they can channel the sound by moving their head and “cupping” the ear.

SC 10. 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, eventually making their way up the Eustachian tube by way of the throat.