Pinna

The pinna (Latin for feather) is the visible part of the ear that resides outside of the head (this may also be referred to as the auricle).

Purpose
The purpose of the pinna is to collect sound. It does so by acting as a funnel, amplifying the sound and directing it to the ear canal. While reflecting from the pinna, sound also goes through a filtering process which adds directional information to the sound (see sound localization, head-related transfer function, pinna notch). The filtering effect of the human pinna preferentially selects sounds in the frequency range of human speech.

Amplification
Amplification of sound by the pinna, tympanic membrane and middle ear structures create a sound 20 dB greater than the sound entering the pinna. This amplification is an important factor in inner ear trauma resulting from elevated sound levels.

Pinna Notch
The pinna works differently for low and high frequency sounds. For low frequencies, it behaves similarly to a reflector dish, directing sounds toward the ear canal. For high frequencies, however, its value is more sophisticatedly reckoned. While some of the sounds that enter the ear travel directly to the canal, others reflect off the contours of the pinna first: these enter the ear canal at a very slight delay. Such a delay translates into phase cancellation where the frequency component whose wave period is twice the delay period, is virtually eliminated. Neighboring frequencies are dropped significantly. This is known as the pinna notch, where the pinna creates a notch filtering effect.

Anatomy
The diagram shows the shape and location of these components:


 * Anthelix (antihelix) forms a 'Y' shape where the upper parts are:
 * Superior crux (to the left of the fossa triangularis in the diagram)
 * Inferior crux (to the right of the fossa triangularis in the diagram)
 * Antitragus is below the tragus
 * Auricular sulcus is the depression behind the ear next to the head
 * Concha is the hollow next to the ear canal
 * Conchal angle is the angle that the back of the concha makes with the side of the head
 * Crus of the helix is just above the tragus
 * Cymba conchae is the narrowest end of the concha
 * External auditory meatus is the opening to the ear canal
 * Fossa triangularis is the depression in the fork of the anthelix
 * Helix is the folded over outside edge of the ear
 * Incisura anterior (auris) is between the tragus and the antitragus
 * Lobe (lobule)
 * Scapha
 * Tragus

Abnormalities
There are various visible ear abnormalities:


 * Bat ear (also known as wingnut ear) &mdash; an ear that sticks out or protrudes
 * Cryptotia (hidden ear) &mdash; upper auricular sulcus not visible
 * Cup deformity &mdash; helical rim is compressed
 * Darwinian tubercle (auricular tubercle) &mdash; a projection from the helical rim
 * Lop ear &mdash; the top of the helical rim folded over
 * Macrotia (also known as big ears, or hypertrophy of the ears)
 * Rim kinks &mdash; a kink of the helical rim
 * Stahl’s bar (also known as Spock ear) &mdash; third crus (in between the superior crux and inferior crux) making the top of the ear pointed