The external auditory meatus forms a significant part of the outer ear. This canal serves as a pathway for sound to travel inward.
What is the External Auditory Meatus?
The external auditory meatus, also known as the ear canal, is a tube that extends from the outer ear toward the eardrum. It measures approximately 2.5 to 3.5 centimeters (about 1 to 1.4 inches) in length in adults and has an S-shaped curve. Its structure is divided into two main parts: the outer third is composed of cartilage, while the inner two-thirds are made of bone. The canal’s lining consists of skin that continues from the auricle, the visible part of the ear. This skin contains hair follicles, particularly in the cartilaginous outer portion, and specialized glands. These include sebaceous glands and ceruminous glands, which work together to produce cerumen, commonly known as earwax.
Where Exactly Is It Located?
The external auditory meatus begins at the opening within the auricle (pinna). Specifically, its entrance is found just in front of a small cartilaginous projection called the tragus. This opening is continuous with the concha, a hollow depression within the auricle that helps direct sound into the canal.
From this external opening, the meatus extends inward into the temporal bone of the skull. It follows an S-shaped path, leading directly to the tympanic membrane, or eardrum. The eardrum marks the boundary between the external ear and the middle ear structures. The anterior wall of the bony part of the canal is near the temporomandibular joint.
How It Contributes to Hearing
The external auditory meatus acts as a conduit for sound waves. It funnels incoming sound waves collected by the auricle directly toward the tympanic membrane, causing it to vibrate. This direct channeling ensures that sound energy efficiently reaches the eardrum, initiating the transmission of sound to the middle ear.
The ear canal also contributes to hearing sensitivity through a phenomenon called resonance. Due to its specific length and shape, the canal naturally amplifies certain sound frequencies, particularly those in the 2000-4000 Hz range for adults. This amplification can boost sound pressure by 30 to 100 times for frequencies around 3 kHz, making humans more sensitive to these sounds, which include many speech frequencies.
The meatus also provides protection for the delicate structures within the ear. Its curved shape and the presence of cerumen and small hairs help to trap dust, debris, and foreign objects, preventing them from reaching the eardrum. This protective barrier also helps shield the inner ear from external temperature fluctuations.
Common Conditions Affecting the EAM
Several conditions can affect the external auditory meatus, often leading to discomfort or temporary hearing changes. One frequent issue is cerumen impaction, where earwax builds up excessively and blocks the ear canal. While earwax is a natural protective substance, its accumulation can cause itching, pain, and muffled hearing.
Another problem is otitis externa, known as “swimmer’s ear.” This condition is an inflammation or infection of the ear canal’s skin, often caused by bacteria or fungi. It occurs when water becomes trapped in the ear canal, creating a moist environment conducive to germ growth, and can result in pain, discharge, and temporary hearing loss.
Foreign objects, particularly by children, also represent a concern. Items like beads or small erasers can become lodged, leading to inflammation, pain, or even infection if not removed. Such obstructions can also affect hearing by blocking the passage of sound waves to the eardrum.