The pinna, also known as the auricle, is the visible, external portion of the ear located on the side of the head. Its primary function is to capture sound waves and direct these acoustic vibrations toward the internal structures of the ear. It acts as a funnel, ensuring sound energy efficiently enters the ear canal.
The Anatomical Structure of the Pinna
The pinna is composed primarily of a single, continuous plate of elastic cartilage. This flexible framework is covered by thin skin, giving the ear its distinct shape and resilience.
The only exception to this cartilaginous composition is the earlobe (lobule), which is made up of skin, adipose tissue, and connective tissue, completely lacking cartilage. The complex topography features numerous ridges and depressions, each with a specific anatomical name.
The prominent outer rim is the helix, running down to the lobule. A second, curved ridge parallel to the helix is the antihelix, which typically forms a Y-shape at its upper end, creating the triangular fossa. The large, deep depression leading directly into the ear canal is the concha. The small, pointed projection anterior to the ear canal is the tragus, while the antitragus sits opposite it, just above the lobule.
The Primary Role in Hearing and Sound Collection
The function of the pinna is to act as a collector, gathering airborne sound waves and channeling them into the external auditory meatus, or ear canal. This funnelling action provides a slight passive amplification of sound before it reaches the eardrum.
Beyond collection, the complex folds and ridges of the pinna are indispensable for sound localization, especially in the vertical plane. As sound waves strike the outer ear, they are reflected, delayed, and filtered by structures like the concha and antihelix. This process creates a unique spectral pattern of peaks and valleys in the sound frequency before it enters the canal.
These spectral changes, which vary based on the sound’s vertical angle of origin, are interpreted by the brain. The brain uses this filtered information as a spatial cue, allowing a person to accurately determine whether a sound is coming from above or below. This acoustic transformation is directly dependent on the individual shape of the pinna.
Common Afflictions and Care
Due to its exposed location, the pinna is susceptible to various forms of trauma and infection. A direct blow can cause an auricular hematoma, where blood collects between the cartilage and the overlying perichondrium (the connective tissue layer providing the cartilage’s blood supply). If this hematoma is not promptly drained, the cartilage can die from lack of blood, leading to tissue deformation known as “cauliflower ear.”
Another common issue is perichondritis, an infection of the perichondrium, which typically spares the cartilage-free earlobe. This infection is frequently associated with trauma, such as high-ear piercings that penetrate the cartilage. The bacteria Pseudomonas aeruginosa is often the culprit in piercing-related perichondritis, causing significant pain, redness, and swelling.
Proper care involves protecting the pinna from physical impact and excessive sun exposure, as its thin skin is vulnerable to ultraviolet damage. For new piercings, meticulous hygiene is necessary to prevent infections that could potentially damage the underlying cartilage. Any sign of severe, spreading redness or swelling following trauma or a piercing should be evaluated immediately to prevent long-term disfigurement.