The pinna is the outer part of the ear, which is individually shaped in each person. It has both functionally important and non-functional parts (for example, earlobe). Diseases of the auricles are often the result of mechanical action, injury, piercings, insect bites, or surgery.
What is an auricle?
The auricle identifies the externally visible part of the ear. Its Latin name is auricle auris. It consists largely of cartilaginous tissue covered with skin. Its function is to receive sound, which is concentrated toward the inner ear by the funnel effect. The elastic cartilage shapes the form of the auricle, which is fused to the skull and covered by a layer of tissue (periosteum). Sensations in the auricle auris are controlled by four different nerves. However, the nonfunctional earlobe is largely insensitive to pain and is therefore often used to draw blood for laboratory tests. Like the ear muscles and the Darwin’s ear cusp, the earlobe no longer exerts any function today. The overall morphology of the auricle is genetically determined and therefore has characteristics specific to each individual.
Anatomy and structure
Each person has individually shaped auricles made of a cartilaginous tissue covered with skin. Their main feature is the conspicuous relief with folds and depressions. The outer edge of the auricle is called the helix. The helix runs parallel to the crescent-shaped anthelix. Both are separated by the scapha, a crescent-shaped indentation. This relief acts as an important filtering system for the impinging sound. The edges of the relief cause refraction and, depending on its frequency, different attenuation of the sound. The shape and size of the auricles also determines the overall visual impression of the face, which may not be physiological, but in many cases has psychological significance. While most animals can move their ears in the direction of the sound sources, their mobility is very reduced in humans. The ear muscles responsible for this have lost all significance in humans and represent only a rudiment. The fleshy skin lobes (ear lobes) in the lower part of the auricle auris have also become functionless. However, each person has individually shaped ear lobes. Overall, the human auricle is as unique as a fingerprint and can be used in criminalistics for identification purposes.
Function and tasks
As mentioned earlier, the relief system of the pinnae provides filtering of incoming sound. Through the refraction and the attenuation of the sound waves, which depends on the frequency, the brain obtains the information about its spatial origin. The elevations and depressions within the auricles give the sound its own timbre depending on its origin. Based on this timbre, the brain can determine whether the sound is coming from the front, the back, the bottom, or the top. However, determining whether the sound source is on the right or left is mediated by other mechanisms. For this purpose, the brain analyzes, among other things, the transit time difference of the sound. Another possibility is to judge the loudness, whereby the sound source facing the ear is usually loudest. In the animal kingdom, there is often the possibility of actively aligning the ears according to the corresponding sound source. This is mediated by the ear muscles. This ability largely no longer exists in humans. In a rudimentary way, some people can wiggle their ears, but this no longer has any physiological significance. For this reason, the auricles are sometimes mistakenly regarded as superfluous organs. However, this is not at all the case, since directional hearing would not be possible without the function of the forward-facing auricles.
Diseases and ailments
Diseases of the auricles are often triggered by external stimuli. For example, injuries, piercings, insect bites, frostbite, or even surgery sometimes result in an othaematoma. The othaematoma is a bloody-serous effusion between the cartilage of the auricle and the overlying connective tissue (perichondrium). Sometimes just lying on a folded over auricle is enough. Often, exposure to force also plays a role. The othematoma manifests itself as a reddish swelling on the front of the auricle auris. Pain usually does not occur.However, the connective tissue may reorganize as a result of the effusion, sometimes resulting in a significant change in the auricle. If the othematoma is not treated, auricular perichondritis may develop. In this case, inflammatory reactions occur within the auricle due to infection with Pseudomonas aeruginosa or, less commonly, Staphylococcus aureus. These infections are very serious because they can completely destroy the cartilage tissue. The disease is accompanied by severe pain and abscess formation. The earlobe may be reddened, but is not subject to the painful inflammatory processes. Treatment of auricular perichondritis is alcohol poultices and antibiotics. Often the auricles also suffer from the so-called chondrodermatitis nodularis helicis. This disease is characterized by nodule formation on the helix or anthelix. These nodules are very painful and quickly enlarge to a diameter of 5-8 mm. After that they remain stable. The causes of this disease are unknown. Besides these acquired diseases, there are also the congenital malformations of the auricles. These malformations manifest as ear cysts, ear tags, ear fistulas or auricular dysplasias. Ear cysts represent cavities in the area of the ear. Ear tags are flap-like skin protrusions on the ear. Auricular dysplasias refer to structural changes in the auricles that can range from purely cosmetic to functional, depending on their severity.
