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Outer ear

life science Maturity 11-13 Next article →

The outer ear, also known as the auris externa, is the visible part of the auditory system. It plays a vital role in the process of hearing. This structure consists of two main parts: the auricle and the ear canal. The auricle, often called the pinna, is the fleshy part on the side of the head. The ear canal, or external acoustic meatus, is the tube leading inward. Together, these components gather sound energy from the environment. They then focus this energy onto the tympanic membrane, which is the eardrum.

The mechanism of the outer ear involves a specific sequence of sound conduction. First, the auricle catches sound waves traveling through the air. These waves move from the bottom of the auricle into the ear canal. This canal acts as a simple tube that conducts vibrations toward the tympanic cavity. As sound travels through this tube, the ear canal amplifies certain frequencies. Specifically, it boosts sounds in the range of 2 kHz to 5 kHz. This amplification is significant because it increases sound pressure by 30 to 100 times.

The auricle is a complex structure made of yellow elastic cartilage. This cartilage is covered with integument, which is the skin. It is connected to the surrounding head area by muscles and ligaments. Within the auricle, there are several intrinsic muscles. These include the helicis major, the helicis minor, and the tragicus. Other muscles include the antitragicus, the transverse muscle, and the oblique muscle. These intrinsic muscles help shape the topography of the ear. They may also function as a sphincter for the external auditory meatus.

Outside the auricle, there are three extrinsic muscles. These are the anterior auricular, superior auricular, and posterior auricular muscles. The superior auricular muscle is the largest of the three. In some mammals, these muscles allow the animal to move its ears to focus hearing. Humans have very little movement in these muscles. The anterior muscle pulls the ear forward and upward. The superior muscle raises the ear slightly and stabilizes the occipitofrontalis muscle. The posterior muscle pulls the ear backward. This muscle can contract and flatten the pinna when a person hears a sudden, surprising sound.

The shape of the outer ear provides essential information about the world. The convolutions, or folds, of the pinna act as a filter. They selectively filter different sound frequencies to provide cues about elevation. For example, the ear transmits more high-frequency components if a sound comes from above. This helps the brain determine if a sound source is elevated. This filtering is especially important because most human speech sounds are distributed around 3 kHz. Because the ear is so sensitive to this range, humans are more prone to hearing loss near this frequency.

Sometimes, the outer ear does not develop in a typical way. These malformations can result from hereditary diseases or environmental factors like radiation and infection. One example is a preauricular fistula, which is a narrow tube near the tragus. Some people are born with genetic syndromes that affect ear development. Konigsmark syndrome involves small ears and a closed ear canal. Goldenhar syndrome affects the ears, eyes, skull bones, and vertebrae. Treacher Collins syndrome causes ear dysplasia and can lead to mixed deafness. Crouzon syndrome is another condition that can cause a closed ear canal.

Medical professionals use various methods to address these ear conditions. Surgery is often used to treat malformations. In some cases, doctors may use artificial prostheses. If a person has a cosmetic defect that does not affect function, it is often repaired after age 6 or 7. For conditions that cause hearing loss, early use of hearing aids can be very important. These tools may help prevent complete hearing loss in children. Understanding these structures helps scientists study how humans interact with sound and how we can protect our hearing.

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