The pinna, also known as the auricle, is the visible, external part of the ear located on the side of the head. This scoop-shaped structure is the outermost component of the hearing apparatus, responsible for gathering sound waves. It funnels these waves toward the opening of the ear canal, which leads to the middle and inner ear structures. The pinna acts as the initial receiver, processing sound before it travels deeper into the auditory system.
Defining the Pinna’s Anatomy
The pinna is primarily a complex structure of elastic cartilage covered by a thin layer of skin, giving it both flexibility and shape. The only part lacking cartilage is the earlobe, or lobule, a soft, fleshy area composed of fatty tissue. This cartilaginous framework forms a series of distinct ridges and depressions that are named anatomical landmarks.
The outermost rim is called the helix, which curves inward and terminates at the lobule. Parallel to the helix is the antihelix, a prominent, C-shaped ridge that typically bifurcates near the top. The large, bowl-like depression that leads directly into the external auditory canal is the concha.
The tragus is a small, flattened prominence situated directly in front of the ear canal opening, partially shielding it. Opposite the tragus, and situated below the antihelix, is the antitragus. The intricate combination of these folds creates the pinna’s unique appearance.
The Pinna’s Core Function
The primary function of the pinna is to act as a collector, capturing airborne sound waves and guiding them into the external auditory canal. Its concave shape and angled position help to gather sound more efficiently than a flat surface would. The pinna also serves to modify the sound waves before they enter the canal, particularly affecting high-frequency sounds above 4 kHz.
This sound modification is accomplished through specific reflections and diffractions caused by the pinna’s complex ridges and depressions. These folds create spectral cues—subtle changes in the sound’s frequency spectrum—that are unique depending on the sound’s direction. The brain interprets these spectral cues, referred to as the Head-Related Transfer Function, to determine the vertical location of a sound source.
The difference in how sound reflects off the pinna when coming from the front versus the back allows the brain to distinguish between these two directions. The reflections from the ridges enable accurate front-back localization. Without the pinna’s shape, the ability to judge elevation and front-back position would be significantly impaired.
Common Variations and Modifications
The pinna exhibits significant natural variation in size, shape, and projection among individuals, with common forms including oval, triangular, and round shapes. “Prominent ears” is a common variation that occurs when the antihelix fold is underdeveloped or the concha is overdeveloped, causing the ear to project further from the head. Another frequently observed variation relates to the lobule, which can either be attached directly to the side of the head or hang freely.
The pinna is also a common site for external modifications, such as cosmetic piercings, which puncture the skin and underlying cartilage. Due to its cartilaginous nature, the pinna is susceptible to injury, particularly blunt force trauma. Repeated trauma, common in contact sports, can lead to hematoma auris, where blood collects between the cartilage and the overlying tissue, potentially resulting in a permanent thickening known as “cauliflower ear.”