ANATOMY OF THE EXTERNAL EAR

THE AURICLE (Ear pinna):

It is the comma shaped structure attached to the side of the head by ligaments and muscles. It is composed of a sheet of fibro-elastic cartilage. The covering skin is closely adherent to the perichondrium on the lateral surface.

Blood supply: The external carotid artery branches: superficial temporal artery, occipital artery, and posterior auricular artery.

Venous drainage: Correspond to the feeding arteries à internal and external jugular veins.

Nerve supply:

• Motor: The facial nerve to the vestigial auricular muscles
• Sensory:

1. The auriculotemporal nerve (from cranial nerve V) to the upper 2/3 of the lateral surface.

2. The lesser occipital nerve (C2) to the upper 1/3 of the medial surface.
3. The greater auricular nerve (C2, 3) to the lower 1/3 of the lateral and 2/3 or the medial surfaces.
4. The facial nerve to the area around the concha at the external meatus.

2- THE EXTERNAL AUDITORY CANAL (Meatus):

It extends from base of the concha (of auricle) to the tympanic membrane (24mm length in adults).

• The lateral third is cartilaginous, directed medially, upwards, and backwards, continuous with the auricular cartilage. Its skin contains hairs, sebaceous and ceruminous glands (secrete wax).
• The medial two thirds are bony, directed medially, downwards and forwards, continuous with the bony walls of the middle ear. Its skin is much thinner than the outer third and contains no hairs or glands.
  

The epithelium of the canal migrate periodically beginning from the center of the tympanic membrane to outside the canal discharging wax and other substances in a self-cleaning action.To examine the external ear, you have to pull the auricle upwards and backwards to straighten the canal and see the drum.

Blood supply:

The external carotid artery branches: superficial temporal artery, occipital artery, posterior auricular artery, and deep auricular branch of the maxillary artery.

Nerve supply: Sensory only

1. Anterior ½: The auriculotemporal nerve.
2. Posterior ½: Arnold’s branch of the vagus nerve.

Lymphatic drainage: The pre and post auricular lymph nodes.

3- THE TYMPANIC MEMBRANE (The Ear drum)

Site:

It is located at the medial end of the external auditory canal, separating the external from the middle ear. It lies at an angle of 55o with the horizontal because the anterior and inferior walls of the external canal are longer than its posterior and superior walls.

Shape:

The drum is oval (about 8 x 10 mm), about 0.1 mm thickness, pearly grey, semi-translucent and concave laterally (towards the external auditory canal) showing the reflected cone of light on examination.

It is divided into two unequal parts:

1. The larger part: called pars tensa which has a thick rolled periphery called “The membranous annulus”.
2. The smaller uppermost part: called pars flaccida or Shrapnell's membrane.

The two parts are separated by two folds: the anterior and posterior malleolar folds.

Minute anatomy:

The ear drum consists of three layers:

• The outer skin layer is continuous with the skin lining of the external auditory canal.
• The middle fibrous layer is well formed in pars tensa and absent in pars flaccida. The fibrous layer has two types of fibers: circular and radial.

The handle (manubrium) of malleus, which is one of the auditory ossicles, is embedded in this layer. Its end lies in the center of the drum called (the umbo).

• The medial mucosal layer is continuous with the mucosal lining of the middle ear.
• For diagnostic purpose the ear drum is divided into 4 sections by two imaginary, line through the handle of malleus and the other passes horizontally through the umbo. (Anterosuperior, anteroinferior, posterosuperior and posteroinferior).

Blood supply: Branches from the external carotid artery.

Nerve supply: Sensory only

• The inner surface: Jacobson’s branch of the glossopharyngeal nerve.
The anterior ½ of the lateral surface: The auriculo temporal nerve.
• 
  
• The posterior ½ of the lateral surface: Arnold’s branch of the vagus nerve.

Category: Anatomy Notes