External ear

The external ear comprises the auricle (or pinna), the external auditory meatus, and the tympanic membrane (eardrum). The auricle concentrates and amplifies sound waves and funnels them through the outer acoustic pore into the external auditory meatus to the tympanic membrane.

Gross anatomy

Auricle (pinna)

The auricle is the part of the ear that projects laterally from the head. It is composed of an irregular concave plate of elastic cartilage and dense connective tissue, covered by skin which contains short hairs (tragi), sebaceous glands, and ceruminous glands.

Structure

The auricle has a complex shape that is composed of several ridges, notches, and grooves (see Figure 1):

• helix: posterior free margin of the auricle
• anthelix: a ridge parallel to the helix
  • crura anthelicis: a pair of limbs located above the external acoustic pore
  • fossa triangularis: tiny depression between the crura
• scaphoid fossa: the depression between the helix and anthelix 
• tragus: prominence in front of the external acoustic pore
  • can be manually pushed back over the pore, to mitigate noise
• antitragus: situated in the lower part of the anthelix and faces the tragus
• intertragic incisure: a notch separating the tragus from the antitragus
• cavum conchae: the deepest depression in the auricle, inferior to the crus of the helix
• cymba conchae: depression surrounded by the crus of the helix below and the inferior crus of anthelix above
• ear lobe: the lowest part of the ear and the only part that does not contain cartilage, situated below the intertragic incisure

Vascular supply

The auricle is supplied by

• the posterior auricular branch of the external carotid artery
• the superficial temporal artery
• a branch from the occipital artery

Innervation

• greater auricular nerve of the cervical plexus supplies the medial auricle and the lateral auricle posterior to the EAC
• auriculotemporal nerve from the mandibular division of the trigeminal nerve (CN V3) supplies the skin of the lateral auricle anterior to the EAC
• sometimes there is a small contribution from the small auricular branch of the vagus nerve (CN X)
• facial nerve (CN VII) innervates the external auricular muscles and probably the auricular skin as well

External auditory meatus

The external auditory meatus is a short S-shaped canal within the tympanic temporal bone leading from the auricle to the tympanic membrane. It is approximately 3 cm long and is lined by skin containing hair follicles (tragi), sebaceous glands, and ceruminous glands (which produce cerumen).

Tympanum

The tympanic membrane consists of two layers of collagen fibers:

• an outer layer with a radial fiber arrangement
• an inner layer with a circular fiber arrangement

It has an outer cover of extremely thin skin and an inner layer of cuboidal epithelium facing the tympanic cavity.