Anatomy and Physiology of the Auditory System

peripheral auditory system

includes the structures from the outer ear through the auditory nerve

central auditory nervous system

begins at the cochlear nucleus in the pons and is bounded at the other end by the auditory centers of the cortex

the term ear refers to the entire peripheral auditory mechanism

1. perception of sound (hearing)

2. detection of changes in spatial orientation (balance)

outer ear

1. pinna

2. external auditory canal

middle ear

1. tympanic membrane

2. ossicles

3. eustachian tube

pinna (aka Auricle) landmarks

1. triangular fossa

2, concha

3. tragus

4. intertragal notch

4, lobe

5, antitragus

6. antihelix

7. helix

external auditory meatus (aka ear canal) length

approximately one inch in adults

external auditory meatus (aka ear canal) shape

curved, irregularly-shaped (roughly S-shaped)

external auditory meatus (aka ear canal) outer (lateral) 1/3 is

cartilaginous

external auditory meatus (aka ear canal) medial 2/3 is

osseous (bony)

isthmus

narrowest point of canal at junction of cartilaginous and bony portions

Lateral, cartilaginous portion of EAC

1. contains ceruminous glands, sebaceous glands, hairs

2. continuous with cartilage of pinna

3. thick skin

medial portion of EAC

1. bony (osseous)

2. covered with very thin skin (epithelial tissue) easily traumatized

3. no sebaceous or ceruminous glands, no hair

4. continuous with the lateral layers of the tympanic membrane

external auditory canal ends at the _____.

Tympanic membrane

outer ear function

1. funnel sound into rest of auditory system

2. assist with front-back localization of sound

3. provide enhancement of mid to high frequencies (about 2500 to 5500 Hz) due to concha and external auditory canal resonance

4. protection of muffle and inner ear against foreign objects, temperature changes, etc

disorders of the outer ear

1. microtia

2. perichondritis

3. injuries

4. carcinoma

5. atresia/stenosis

6. impacted cerumen

7. foreign objects

8. external otitis

9. collapsing ear canal

microtia

1. pinna disorder

2. congenital

3. malformation of the pinna, typically abnormally small pinna, absence of landmarks

4. more often unilateral by 4/1, more often on the right side of face and in males

5. surgical repair for cosmetic purposes

anotia

absence of the ear

perichondritis

1. penna disorder

2. acquired

3. can lead to invasion of cartilage

4, edema, redness, tenderness

5. carcinoma

6. injuries - frostbite, blunt trauma, infection of ear piercing

atresia

1. congenital

2. rarely acquired by trauma

3. acquired:

- impacted cerumen

- foreign objects

- external otitis

- stenosis (can also be congenital)

- tumors

4. collapsing ear canal

5. complete or partial absence or closure of the external auditory canal