Unit 1 study cards (middle ear)

Question 1

Middle Ear

Answer 1

A Hard-walled, air filled cavity called the Tympanic cavity.

Contains the Ossicular Chain (3 smallest bones in the body).

Contains Air that is exchanged via the Eustachian tube allowing for equal pressure on both side of the tympanic membrane.

Question 2

Middle Ear (Mode of Operation)

Answer 2

Mechanical Vibration = movements of the ossicular chain transmitting energy to the inner ear.

the middle ear is a TRANSDUCER

Question 3

Ossicular Chain

Answer 3

Suspended in the middle ear space by 4 ligaments and 2 membranes. The following that make up the Ossicular Chain attach to each other but not directly to any other bones.

Malleus (hammer)
Incus (anvil)
Stapes (stirrup, the smallest bone in the body)

Ligaments form the axis of rotation for the chain

The role of the ossicles in the middle ear is to MATCH the HIGH impedance of the fluid filling the inner ear to the LOW impedance of the air in the ear canal and facilitate an effective transfer of energy to the inner ear.

Question 4

Malleus (hammer)

Answer 4

Has an attachment on anterior surface for the… Tensor Tympani Muscle: this muscle pulls the Ossicular chain in an anterior direction

Question 5

Incus (anvil)

Answer 5

articulates with Stapes in a true ball and socket joint.

Question 6

Stapes (stirrup)

Answer 6

Has an attachment on anterior surface for the…Stapedius Muscle: this muscle pulls the Ossicular chain in a posterior direction

smallest bone in the human body

Question 7

Stapedius Muscle

Answer 7

Length: 6mm long - smallest muscle in the human body

Innervation: CNVII (Cranial Nerve 7, the Facial Nerve)

AGONIST AND ANTAGONIST

Question 8

Tensor Tympani Muscle

Answer 8

Length: 25mm long

Innervation: CNV (Cranial Nerve 5, the Trigeminal Nerve)

can be activated by a puff to the face

AGONIST AND ANTAGONIST

Question 9

Middle ear “box”

Answer 9

Memorize this 3D structure for FINAL.

Question 10

Middle ear Functions

Answer 10

1. Impedance Matching (boosting the pressure)
2. Selective Oval Window Stimulation
3. Pressure Equalization

Question 11

Impedance Matching (Boosting the pressure)

Answer 11

It is the process by which the middle ear effectively transfers sound vibrations from the air (low impedance) to the fluid-filled inner ear (high impedance)

Question 12

3 Mechanisms of Impedance Matching (Boosting the pressure)

Answer 12

1.) ** Area Ratio effect**
2.) The Ossicular Lever effect
3.) Buckling effect

All three mechanisms combined = and increase of about 32 dB

Question 13

Eustachian Tube

Answer 13

The Eustachian tube connects the middle ear to the back of the nose and throat (pharynx). Its job is PRESSURE EQUALIZATION. It opens during a pressure imbalance to ventilate the middle ear space and equalize pressure on both sides of the tympanic membrane.

The cartilage is closed until opened by the tensor veli palatini muscle when yawning, sneezing, or shouting.

Question 14

** Area Ratio effect**

Answer 14

There is a big difference in Surface Area between the Tympanic membrane -LARGE (eardrum) and Stapes footplate - SMALL (oval window).

SO, by increasing pressure on the Stapes footplate/oval window, we can effectively transfer sound vibrations from the air (low impedance) to the fluid-filled inner ear (high impedance)

Question 15

2.) The Ossicular Lever effect

Answer 15

The ossicles act like a lever and they transmit vibrations from the Tympanic membrane/eardrum to the Oval window of the middle ear.

This bent lever (ossicles) increases force: F1xD1=F2xD2 (Seesaw)

So, this lever can effectively transfer sound vibrations from the air (low impedance) to the fluid-filled inner ear (high impedance)

Question 16

3.) Buckling effect

Answer 16

The way the tympanic membrane (eardrum) naturally curves (buckles), causes a greater force to be applied to the ossicles (tiny bones) when sound waves hit it, essentially amplifying the sound by concentrating the pressure on a smaller area around the handle of the malleus (hammer bone) due to its curved shape.

increases pressure by a factor of 2

So, this OTHER lever can effectively transfer sound vibrations from the air (low impedance) to the fluid-filled inner ear (high impedance)

Question 17

What is the middle ear muscle reflex?

Answer 17

It’s an INVOLUNTARY CONTRACTION of the middle ear muscles (stapedius muscle and Tensor Tympani) in response to LOUD SOUNDS.

This reflex protects the inner ear from damage by loud noises.

In response to a LOUD SOUND…
-) The Stapedius muscle will contract and pull the stapes footplate/ossicular chain in a posterior direction (outward and downwards away from the oval window).

-) The Tensor Tympani muscle will contract and pull the malleus bone/ossicular chain in an anterior direction.

TOGETHER, the muscles increase the impedence of the middle ear system by increasing the stiffness of the ossicular chain.

Latency: 10-150 msec so no effect on shot sounds

Question 18

Theories of the middle ear muscle reflex (very useful in clinical audiology)

Answer 18

1.) Protection
-affects transmission of low frequency sounds to the inner ear. maybe also protect middle ear? make sure ossicular chain doesn’t move so violently to protect middle ear.

2.) Reduction of bone conducted sound
-reduces sound conducted via skull bones to inner ear. When we speak we hear ourselves through auditory pathways but we also hear from bone conduction. (Too much bone conducted sound may be problematic while we are speaking).

3.) Prevention of distortion
-may keep ossicular joints from flexing, ensuring no distortion of signal.