Anatomy and Physiology

What energy type is the outer ear?

Acoustic

What energy type is the middle ear?

Mechanical

What energy type is the cochlea?

Hydraulic and electrochemical

The pinna is responsible for a 10dB boost at _____ Hz

5000

Any pathology, absence, or malformation of the outer ear may result in some loss of hearing acuity at _____-_____Hz

2000-5000Hz

The external auditory canal provides a 12dB boost at _____Hz

3000Hz

What portion of the ear canal is cartilaginous versus bony?

Outer 1/3 is cartilaginous, inner 2/3 is bony

What pH is maintained in the ear canal and what does it do?

pH of 6.1

Slightly antifungal, antibacterial, and repellant to insects

What are the 3 layers of the tympanic membrane?

1. Epithelial

2. Fibrous

3. Mucosal

What are the 3 primary ratios that deal with the impedance mismatch from the TM to the stapes?

1. Area ratio (the TM is 17 times larger than the area of the stapes)

2. Ossicular lever ratio

3. Curved membrane ratio (buckling of the TM)

How much gain is created by the 3 ratios for the impedance mismatch?

33 dB SPL

How many turns are in the cochlea?

2 3/4

What are the 3 sections of the cochlea (scalae)?

1. Scala vestibuli (connects to oval window)

2. Scala media (AKA cochlear duct)

3. Scala tympani ( articulates with the round window)

What fluid is the scala vestibuli and scala tympani?

Perilymph

What is the chemical make-up of perilymph?

High sodium, low potassium

What fluid is the scala media?

Endolymph

What is the chemical make-up of endolymph?

High potassium, low sodium

What fluid is in the vestibular aqueduct?

Endolymph

Which membrane divides the scala vestibuli from the scala media?

Reissner’s membrane

Which membrane divides the scala media from the scala tympani?

Basilar membrane

Describe the basilar membrane shape and stiffness

Narrow at base, wide at apex

Stiff at base, floppy at apex

Describe outer hair cells

12,000 per cochlea

Resting potential of -70mV; k+ channels

Fewer afferent connections, many efferent connections

Describe inner hair cells

3,500 per ear

Resting potential of -40mV; k+ and Na+ channels

Majority 90-95% are afferent connections