The external ear (or outer 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.
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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):
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helix: posterior free margin of the auricle
crus helicis: anterior terminal portion of the helix superior to the external acoustic pore
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antihelix: a ridge parallel to the helix
crura antihelicis: a pair of limbs located above the external acoustic pore
fossa triangularis: tiny depression between the crura
scaphoid fossa / scapha: the depression between the helix and antihelix
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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 antihelix 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 antihelix above
ear lobe (lobule): the lowest part of the ear and the only part that does not contain cartilage, situated below the intertragic incisure
External auditory meatus
The external auditory meatus is a short S-shaped canal within the tympanic temporal bone leading from the external acoustic pore of 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 (or tympanum) consists of two layers of collagen fibers:
It has an outer cover of extremely thin skin and an inner layer of cuboidal epithelium facing the tympanic cavity.
The tympanic membrane, is anatomically part of, and represents, the most medial extent of the external ear.
an outer layer with a radial fiber arrangement
an inner layer with a circular fiber arrangement
Arterial supply
The auricle is supplied by:
the posterior auricular branch of the external carotid 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
Development
The external ear is developed from six auricular hillocks arising from the first and second pharyngeal arches. The first pharyngeal arch giving rise to hillocks 1 to 3 and second forming auricular hillocks 4 to 6, the antihelix, antitragus and concha are derived from the latter 3.
Clinical importance
The external ear plays an important role in conduction of sound into the external auditory canal, the unique shape of the ear helps to facilitate this. A number of ear deformities exist and intricate knowledge of ear anatomy is required in recontructive surgery, not only to restore aesthetic appearance of the ear but also to ensure functionality.
Being predominantly cartilage with little blood supply it is particularly prone to developing infections which may lead to a number of complications including keloids, nodules, cysts, or cauliflower ear. Hence it is now becoming ever more important for the everyday clinican to be familiar with the blood supply, lymphatics and innervations in order to appropriately treat and prevent complications.
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