Facebook Twitter RSS Reset

Anatomy Physiology of External Ear

ANATOMY OF THE EXTERNAL EAR

The external ear consists of the expanded portion named the auricle(or pinna) and the external auditory meatus. The external ear is separated from the middle ear by a disk-like structure called the tympanic membrane. The auricle projects from the side of the head and serves to collect the vibrations of the air by which sound is produced; the external auditory canal   leads inward from the bottom of the pinna and conducts the vibrations to the tympanic cavity.

Anatomy-of-External-Ear

Auricle or Pinna

The Auricle, also called pinna or auricula, is commonly known as the ear and it resides outside the head. The pinna is formed in the 20th week of embryological development. The auricle is a convoluted plate of elastic cartilage covered with skin and fixed in position by muscles and ligaments. The major landmarks of the auricle are the helix, the antihelix, the scaphoid fossa, triangular fossa, the tragus and the antitragus, the concha, which is the funnel like depression leading into the external canal, and the lobule. The lobule is the only portion of the auricle that contains no cartilage. Strong hairs project from the tragus, particularly in men after middle age, forming a tuft like a goat. The cartilage of the auricle is continuous with that of the external canal.

External Auditory Canal

  • The External Acoustic Meatus extends from the bottom of the concha to the tympanic membrane  . It is about 4 cm. in length if measured from the tragus; from the bottom of the concha its length is about 2.5 cm.
  • It forms an S-shaped curve, and is directed at first inward, forward, and slightly upward; it then passes inward and backward , and lastly is carried inward, forward, and slightly downward. It is an oval cylindrical canal, the greatest diameter being directed downward and backward at the external orifice, but nearly horizontally at the inner end.
  • It presents two constrictions, one near the inner end of the cartilaginous portion, and another, the isthmus, in the osseous portion, about 2 cm. from the bottom of the concha.
  • The tympanic membrane, which closes the inner end of the meatus, is obliquely directed; in consequence of this the floor and anterior wall of the meatus are longer than the roof and posterior wall.
  • The external acoustic meatus is formed partly by cartilage and membrane, and partly by bone, and is lined by skin.
  • The lateral third is an elastic cartilaginous and dense fibrous framework to which thin skin is attached.
  • The skin of the canal contains hair, sebaceous glands, and ceruminous glands, which secrete a brown, wax-like substance called cerumen (ie, ear wax).
  • The ear’s self-cleaning mechanism moves old skin cells and cerumen to the outer part of the ear.
  • Just anterior to the external auditory canal is the temporomandibular joint. The head of the mandible can be felt by placing a fingertip in the external auditory canal while the patient opens and closes the mouth.

PHYSIOLOGY OF THE EXTERNAL EAR

 

  1. Localization of sound: The external ear is commonly thought to collect the sound waves and funnel them into the ear canal. But at least in human beings, where the pinna is rather small, it is unlikely that this function is significant. A far more important function of the pinna is to help in the localization of sound.
  1. Provide Resonance: The ear canal is not straight but tortuous, therefore the resonance frequency is not so sharply defined. But since the resonance in the ear canal boosts sounds of the frequency range 2000-5000 Hz by about 15 dB, the characteristic length of the ear canal may be considered to contribute to the enhanced sensitivity of the ear in this frequency range.