The hollow center of the auricle is the concha of the auricle. The external acoustic meatus leaves from the depths of this area.
Just anterior to the opening of the external acoustic meatus, in front of the concha, is an elevation (the tragus). Opposite the tragus, and above the fleshy lobule, is another elevation (the antitragus). A smaller curved rim, parallel and anterior to the helix, is the antihelix.
Numerous intrinsic and extrinsic muscles are associated with the auricle:
The intrinsic muscles pass between the cartilaginous parts of the auricle and may change the shape of the auricle.
The extrinsic muscles, the anterior, superior, and posterior auricular muscles, pass from the scalp or skull to the auricle and may also play a role in positioning of the auricle (see Fig. 8.56).
Both groups of muscles are innervated by the facial nerve [VII].
Sensory innervation of the auricle is from many sources (Fig. 8.115):
The outer more superficial surfaces of the auricle are supplied by the great auricular nerve (anterior and posterior inferior portions) and the lesser occipital nerve (posterosuperior portion) from the cervical plexus and the auriculotemporal branch of the mandibular nerve [V3] (anterosuperior portion).
The deeper parts of the auricle are supplied by the vagus nerve [X] (the auricular branch) and the facial nerve [VII] (which sends a branch to the auricular branch of the vagus nerve [X]).
The arterial supply to the auricle is from numerous sources. The external carotid artery supplies the posterior auricular artery, the superficial temporal artery supplies anterior auricular branches, and the occipital artery supplies a branch.
Venous drainage is through vessels following the arteries.
Lymphatic drainage of the auricle passes anteriorly into parotid nodes and posteriorly into mastoid nodes, and possibly into the upper deep cervical nodes.
The external acoustic meatus extends from the deepest part of the concha to the tympanic membrane (eardrum), a distance of approximately 1 inch (2.5 cm) (Fig. 8.116). Its walls consist of cartilage and bone. The lateral one-third is formed from cartilaginous extensions from some of the auricular cartilages and the medial two-thirds is a bony tunnel in the temporal bone.
Throughout its length the external acoustic meatus is covered with skin, some of which contains hair and modified sweat glands producing cerumen (earwax). Its diameter varies, being wider laterally and narrow medially.
The external acoustic meatus does not follow a straight course. From the external opening it passes upward in an anterior direction, then turns slightly posteriorly still passing upward, and finally, turns again in an anterior direction with a slight descent. For examination purposes, observation of the external acoustic meatus and tympanic membrane can be improved by pulling the ear superiorly, posteriorly, and slightly laterally.
Sensory innervation of the external acoustic meatus is from several of the cranial nerves. The major sensory input travels through branches of the auriculotemporal nerve, a branch of the mandibular nerve [V3] (anterior and superior walls), and in the auricular branch of the vagus nerve [X] (posterior and inferior walls). A minor sensory input may also come from a branch of the facial nerve [VII] to the auricular branch of the vagus nerve [X].
The tympanic membrane separates the external acoustic meatus from the middle ear (Figs. 8.117 and 8.118). It is at an angle, sloping medially from top to bottom and posteriorly to anteriorly. Its lateral surface therefore faces inferiorly and anteriorly. It consists of a connective tissue core lined with skin on the outside and mucous membrane on the inside.