The external ear is composed of the auricle, commonly called the pinna, and the external auditory canal, structures that capture and direct sound waves toward the middle ear.
Anatomy of the Auricle
The auricle is the visible portion of the external ear and exhibits a complex framework of elastic cartilage covered by thin skin.
Structural Components
This cartilage framework provides the necessary rigidity to maintain the ear's shape while allowing slight flexibility for movement.
The helix forms the prominent outer rim of the ear.
The antihelix is a curved ridge located just inside the helix.
The earlobe, or lobule, is the soft, fleshy lower portion that lacks cartilage.
The External Auditory Canal
The external auditory canal is a tube-like structure extending from the auricle to the eardrum, serving as a sound conduit.
Physical Characteristics
Its walls are formed by a combination of skin and cartilage, creating a slightly angled pathway approximately 2.5 centimeters long in adults.
The outer third is composed of flexible cartilage.
The inner two-thirds are composed of bone lined with skin.
Tiny hairs and ceruminous glands produce earwax to trap debris.
Function in Hearing
These structures work together to gather acoustic energy and funnel it efficiently to the tympanic membrane.
Amplification and Localization
The shape of the auricle acts as a natural amplifier, particularly for frequencies around 2 to 5 kHz, which are crucial for speech recognition.
The asymmetrical design of the external ear aids the brain in determining the vertical location and direction of incoming sounds.
Clinical Significance
Understanding the composition of the external ear is essential for diagnosing conditions that affect hearing and comfort.
Common Conditions
Inflammation of the canal, known as otitis externa, often occurs due to moisture retention or minor trauma.
Impacted earwax can block the canal, leading to temporary hearing loss or tinnitus.
Genetic variations in the auricle's shape may contribute to issues such as cauliflower ear in contact sports.
Variations and Adaptations
Human ears display significant variation in size and form, yet they maintain the fundamental composition described above.
Evolutionary Perspective
The large, mobile pinna found in many mammals has been reduced in humans, though it retains the ability to move slightly to capture sound.
