Outer ear


The auricle, which is also known as the pinna, and the external acoustic canal comprise the outer ear. The external acoustic meatus is created by the combination of the fleshy tube which lays inside the bony tube. Easily discernable with the naked eye, the pinna can be detected along the outside of the head, and is varied mildly in shape and size from individual to individual. A basic structural frame of cartilage is then covered with a stretchy connective tissue, and finally covered with skin. The ridge of the pinna is known as the helix. The fleshy lower section that flexes and hangs free is known as the earlobe, and is the only section of the out ear that is free of the cartilage framework. The auricle is held to the head with ligaments, as well as a combination of muscles which lack strength or high definition. These muscles are attached to the outer ear along the superior, anterior, and posterior segments of the ear.


The auricle receives the necessary blood supply via posterior auricular artery and the occipital artery. These are extensions which branch off from the external carotid artery and the superficial temporal artery. The pinna is designed structurally to help encourage sound waves to enter the ear, with its mild funneling style it acts somewhat like a sound wave scoop. The external acoustic canal measures approximately 1 inch in length and appears to hold the shape of a near S. The canal itself has a slight incline, extending upward toward the tympanic membrane. The canal is lined with sebaceous glands and fine, thin hairs that nearly circle the entrance, which helps to keep foreign objects from entering the ear canal.


Outer Ear
Image: Outer Ear


The ceruminous glands are those which are buried deeper in the ear canal, secrete wax for ear protection and seeps out wax to keep the tympanic membrane soft, pliable, and waterproof. The secreted wax serves as an additional barrier to small foreign objects entering the ear canal. Cerumen, also known as ear wax, is thought to be an insect repellant.

The tympanic membrane measures only about 1 centimeter in diameter. It is quite thin despite its double layering, and is really a dividing element designed by epithelial cells. It segregates the external acoustic canal from the middle ear. The outer concave layer is designed out of stratified squamous epithelium while the inner convex layer is designed of low columnar epithelium. A firm connective tissue layer rests in between the epithelial layers.

The tympanic membrane is well innervated, receiving the auriculotemporal branch from the mandibular nerve and the auricular nerve branched from the vagus nerve. There are additional branches from the facial nerve and the glossopharyngeal nerve which innervate the tympanic membrane. This excessive innervation makes the tympanic membrane remarkably sensitive to painful stimulus.
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