A&P Outer Ear

Auditory Pathway (Ear to Brain #8)

1. VIII Nerve (sensory only - afferant)

2. Cochlear nuclei

3. Trapezoid body

4. Superior olivary complex

5. lateral lemniscus

6. Inferior colliculi

7. Medical geniculate nucleus

8. Primary auditory cotex

Outer Ear: 3 main parts

1. Pinna

2. External auditory meatus/canal

3. Tympanic membrane

Pinna: function

1. Collection and localization of sound energy

2. Keep dirt/insects out via epithelial tissue and fine hairs

3. Serves as a diagnostic marker of some genetic conditions

Pinna: landmarks (7)

1. Helix

2. Auricle tubercle

3. Antihelix

4. Cavum Concha

5. Tragus

6. Antitragus

7. Lobe

Helix: location

lateral superior margin

Auricle tubercle: location

bulge on the helix

Antihelix: location

immediately anterior to the helix and marks the entrance to the concha

Cavum concha: location

deepest depression on the pinna and leads into the external auditory meatus

Tragus: location

flap of epithelium covered cartilage the is able to cover the entrance to the meatus

Antitragus: location

inferior segment of cartilage just above the lobe

Lobe: location

non-cartilaginous segment of tissue at the inferior border of the pinna

Mastoid process

1. Bony ridge behind the auricle (ear)

2. part of the temporal bone

3. Provides support to external ear and posterior wall of middle ear cavity

External auditory meatus

1. Apx 1.25in or 2.5-3cm long (S shaped but anatomic variation)

2. Outer 1/3= cartilage (lined w/cerumen glands and cilia)

3. Inner 2/3= bony meatus of temporal bone (isthmus narrowest portion of canal .5cm from tympanic membrane)

Tympanic membrane: function

1. vibrates in response to sound

2. changes acoustic energy into mechanical energy

TM: form

Three Layers

1.Superficial - continuous with epithelial lining of EAM

2. Medial - fibrous tissue that provides structure

3. Deep - continuous with lining of middle ear

Outer ear transfer function

1. amount of boost varies across frequency

2. net gain of 20 dB at 3000 Hz

3. varies across individuals (women and children often have shorter ear canals)

Microtia

1. underdevelopment of Pinna and usually EAM (doesn’t necessarily indicate issues with middle or inner ears)

2. reconstruction is rarely satisfactory but bone anchored hearing aids/prosthesis may give good results

Atresia

1. EAM absent or severely underdeveloped (can be accompanied with underdeveloped pinna)

2. reconstruction may be successful if middle ear is relatively normal