Outer Ear Middle Ear Inner Ear. 1. OUTER EAR consists of the PINNA and the EXTERNAL AUDITORY CANAL. The pinna is the cartilage of the ear; it.

Outer Ear Middle Ear Inner Ear

1. OUTER EAR consists of the PINNA and the EXTERNAL AUDITORY CANAL.

The pinna is the cartilage of the ear; it acts as a funnel to capture the sound.

If you cup your hands to your ears (do it now), you’ll notice the sound of my voice is louder.

If you rolled up a piece of paper like a funnel and put it to your ear, it functions like the pinna.

The transmission of sound vibrations through the outer ear occurs chiefly through AIR.

The Outer (External) Ear

Figure 16.17a

2. MIDDLE EAR is an AIR filled space with structures.

The TYMPANIC MEMBRANE (ear drum) vibrates in response to sound.

Attached to it are 3 bones: The MALLEUS (hammer), INCUS (anvil), and the STAPES (stirrup) are the smallest bones in the body. Together, they are only one inch long.

Their function is to amplify sound vibrations. The malleus vibrates the incus, which vibrates the stapes.

Structures of the Middle Ear

Figure 16.17b

The middle ear is open to the nasopharynx by way of the AUDITORY TUBE (also called eustachian tube or nasopharyngeal tube), which is only the thickness of a pencil lead.

If this tube is closed, the ears feel plugged up. The function of the auditory tube is to equalize the

pressure of the middle ear and the outside air so the ear bones can vibrate.

Tubes are put in the tympanic membrane to drain fluids in kids with frequent ear infections.

Structures of the Middle Ear

Figure 16.17b

3. INNER EAR exists within the temporal bone (petrous portion).

It is a complex structure. It is located in a bony cavity called the BONY LABYRINTH (“maze”).

The bony labyrinth is filled with a fluid called PERILYMPH, which is similar to CSF. The bony labyrinth is the only place where perilymph is found.

The Inner (Internal) Ear

Figure 16.17b

Inner Ear• Within the bony labyrinth is a snail-shaped

structure, called the MEMBRANOUS LABYRINTH, which is filled with ENDOLYMPH.

• The snail-shaped structure is divided into two main components. One is the COCHLEA (“snail shell”). This is responsible for hearing.

• The other structure is responsible for balance and consists of three parts:– Semicircular Canals– Utricle– Saccule

Semicircular canals:

Utricle

Saccule

Cochlea

Stapes

Vestibulocochlear nerve

Instead of drawing the cochlea curled up, I’ve drawn it laying out straight.

Inside the cochlea are special neurons called HAIR CELLS; their axons form CN VIII.

The stapes is attached to the OVAL WINDOW, and vibrations cause the endolymph to vibrate; the hair cells here transmit this vibration.

Therefore the HAIR CELLS in this region are receptors for HEARING.

COCHLEA

Hair Cells

Low frequencies (like the longer strings of a piano) cause a response in the tip of the cochlea.

High frequencies cause a response at the larger end of the cochlea.

The axons of the hair cells form CN VIII, the VESTIBULOCOCHLEAR NERVE, which takes the signals to the brain.

Therefore, the cochlea is where the hearing receptors are located, so the cochlea is responsible for all of the hearing of sounds.

However, the ear does more than just hear; it is also responsible for balance and equilibrium.

This system regulates balance. It is also within the inner ear. SEMI-CIRCULAR CANALS (Three of them,

all in different planes) determine movement in three planes.

Within each semi-circular canal is endolymph and hair cells, whose axons go to the cerebellum.

When you move in one direction, like sliding across the room, the fluid sloshes like a cup of coffee, and it triggers the hair cells.

Attached to the semi-circular canals are two joined structures called the UTRICLE and the SACCULE.

These also contain HAIR CELLS and ENDOLYMPH.

Within the endolymph here are OTOLITHS (“ear rocks”) which are calcium deposits.

When you stand perfectly upright, these otoliths fall directly down and bend the HAIR CELLS (a special type of neuron) on the lower cells. When you tip your head to the side, they will stimulate the hairs on that side.

The otoliths stimulate the hair cells to tell you what position your head is in and give you a sense of equilibrium.

Therefore, the HAIR CELLS in this region are receptors for equillibrium and the OTOLITHS are an essential component of this process.

Anatomy and Function of the Otoliths

Figure 16.21b

Inflammation of the semi-circular canals give you a sense of motion when you’re not moving = VERTIGO (dizziness) or LABYRINTHITIS.

This can be debilitating. Sometimes only one canal is affected, so

you only get dizzy if you turn your head one way.

When your eyes get one set of information that conflicts with the vestibular structures, such as when you are high up in the air or strobe lights flashing, or reading in a car.

Whether the vertigo is from visual or vestibular disturbances, your body interprets the signals as a poison invasion, so it initiates a vomit reflex.

“Cauliflower Ear”Hematoma auris or Traumatic auricular hematoma

Common in boxers and wrestlers

A blood clot or other fluid collects under the perichondrium. This separates the cartilage from the overlying perichondrium that is its source of nutrients, causing the cartilage to die.

This leads to a formation of fibrous tissue in the overlying skin.

Conductive hearing loss happens when there is a problem conducting sound waves through the outer ear, tympanic membrane (eardrum) or middle ear (ossicles). It may be caused from excess wax, damaged eardrum, or arthritis of the ossicles.

Hearing loss from nerve damage (sensorineural) is a problem in the vestibulocochlear nerve (Cranial nerve VIII), the inner ear, or central processing centers of the brain.

Weber Test: only tests unilateral problems. A tuning fork is touched to the middle of the forehead:◦ Nerve damage: sound is heard louder in the

normal ear because the damage is to the nerve, so bone conduction of the sound is ineffective.

◦ Conductive hearing loss: sound is heard louder in the problem ear (earwax, etc) because reflected soundwaves cannot escape the ear canal, so they penetrate deeper into the inner ear.

Performed by placing a vibrating tuning fork on the mastoid process until sound is no longer heard, the fork is then immediately placed just outside the ear. Normally, the sound is audible at the ear, indicating a positive Rinne test.

If they cannot hear the sound at the ear, it is a negative Rinne test, and indicates Sensorineural hearing loss

A cochlear implant is a small, complex electronic device that can help to provide a sense of sound to a person who is profoundly deaf or severely hard-of-hearing. The implant consists of an external portion that sits behind the ear and a second portion that is surgically placed under the skin. An implant has the following parts:

A microphone, which picks up sound from the environment. A speech processor, which selects and arranges sounds picked up

by the microphone. A transmitter and receiver/stimulator, which receive signals from

the speech processor and convert them into electric impulses. An electrode array, which is a group of electrodes that collects the

impulses from the stimulator and sends them to different regions of the auditory nerve.

An implant does not restore normal hearing. Instead, it can give a deaf person a useful representation of sounds in the environment and help him or her to understand speech.

http://video.yahoo.com/watch/421542/2418338

Excess noise Frequent sinus infections (or allergies) Medicines

◦ Excess Tylenol or aspirin, antibiotics, sedatives, antidepressants)

Lack of blood flow (anemia, hypertension, diabetes, age) Drugs (marijuana, caffeine) Foods (soy, wheat, chocolate, red wine)

Symptoms of nerve damage:◦ Tinnitus: ringing in the ears◦ If damage is not severe, axons can regenerate and tinnitus will

go away

The rest of this lecture is not test material

The stapes becomes fixed, cannot move, and dampens sound conduction.

Stapedotomy: A portion of the stapes is removed and replaced with a titanium-nickel prosthesis.

Stapedotomy

Stapedotomy

Prosthesis

Stapedotomy

Hearing damage from headphones is more common than from loudspeakers, because people listen at higher volumes.

Even at comparable volumes, hearing damage from headphones is higher than with loudspeakers, due to the close coupling of the transducers to the ears.

How long can you listen at certain volumes without damage?

90 dbA 8 hrs

92 dbA 6 hrs

95 dbA 4 hrs

97 dbA 3 hrs

100 dbA 2 hrs

102 dbA 1.5 hrs

105 dbA 1 hr

110 dbA 0.5 hr

115 dbA 0.25 hr or less

60 dB Everyday conversation, ringing telephone.

70 dB Restaurant.

80 dBHeavy city traffic, alarm clock at 2 feet, factory noise, vacuum cleaner, garbage disposal.

90 dBSubway trains, motorcycle, workshop tools, lawn mower.

100 dB Chain saw, pneumatic drill.

110 dB Dance club.

120 dBRock concert speaker sound, sandblasting, thunderclap.

130 dB Jet take off.

140 dB gunfire Nerve damage occurs immediately

150 dB rock music peak