The auricle, also known as the pinna, is the external, visible part of the ear. It is composed primarily of elastic cartilage covered by skin, giving it a flexible yet durable structure. The auricle plays a role in shaping the external ear’s contour and is involved in directing sound waves into the ear canal. It consists of several distinctive landmarks, including the helix, antihelix, tragus, antitragus, and lobule. These structures contribute to its unique shape, which is critical in differentiating sound directions and sources.
Location
The auricle is located on the lateral sides of the head, positioned at the external surface of the ear. It is attached to the skull at the temporal bone, just outside the external auditory canal. The auricle sits at approximately the level of the eyes and is the outermost portion of the auditory system, exposed on both sides of the head.
Structure and Anatomy
Overview
The auricle (or pinna) is the visible part of the external ear, composed mainly of elastic cartilage covered by skin. Its intricate structure consists of various folds, ridges, and depressions that give it its unique shape. The auricle serves as the outermost component of the auditory system and connects to the external auditory canal. It is responsible for shaping and funneling sound waves into the ear canal, but its anatomical structure is more intricate than its simple appearance suggests.
Cartilaginous Framework
The primary structural component of the auricle is elastic cartilage. This type of cartilage provides flexibility while maintaining the auricle’s shape. The only part of the auricle without cartilage is the earlobe (lobule), which consists of adipose tissue, skin, and connective tissue. The cartilage of the auricle forms a continuous sheet, providing support for the various ridges and folds that define its anatomy.
Skin Covering
The entire auricle is covered by a layer of thin skin, which is tightly adherent to the cartilage in most areas. This skin is highly vascular and contains sebaceous and sweat glands. The skin is thicker and looser in the earlobe, where it is free from the underlying cartilage, making the lobule soft and pliable.
Key Anatomical Landmarks
- Helix: The helix is the prominent outer rim of the auricle, forming a curved boundary that begins at the root of the auricle and curves upward and forward. It then arches downward and terminates near the earlobe. The helix encloses much of the auricle’s structure.
- Antihelix: Situated parallel and interior to the helix, the antihelix is a Y-shaped ridge. It has two branches: the superior crus, which points upward, and the inferior crus, which points toward the center of the ear. The antihelix is a major ridge that separates the deeper concave regions of the auricle.
- Concha: The concha is a large bowl-shaped depression located in the center of the auricle. It can be divided into two parts: the cymba conchae (upper portion) and the cavum conchae (lower portion). The concha leads directly into the external auditory canal and is surrounded by the helix and antihelix.
- Tragus: The tragus is a small, pointed flap of cartilage that projects outward from the front of the auricle, covering part of the external auditory canal. It is positioned anterior to the concha and plays a role in sound wave entry.
- Antitragus: Opposite the tragus, the antitragus is a small cartilaginous projection located just above the earlobe. It sits adjacent to the concha and the tragus, separated from the latter by a deep notch known as the intertragic notch.
- Lobule: The lobule (earlobe) is the soft, fleshy, inferior portion of the auricle. It contains no cartilage and is composed of fatty tissue, skin, and connective tissue. It is the only part of the auricle that can be easily manipulated and stretched, making it a common site for ear piercings.
Blood Supply
The auricle receives its blood supply from two main arteries:
- The posterior auricular artery, a branch of the external carotid artery, supplies the posterior aspect of the auricle.
- The superficial temporal artery, another branch of the external carotid artery, supplies the anterior part of the auricle.
These arteries ensure that the skin and cartilage of the auricle receive adequate oxygen and nutrients.
Venous Drainage
Venous drainage of the auricle follows the arterial supply and occurs through the posterior auricular vein and the superficial temporal vein. These veins eventually drain into the external jugular vein.
Innervation
The auricle is innervated by several nerves:
- The greater auricular nerve supplies the lower part of the auricle and the posterior region.
- The auriculotemporal nerve supplies the anterior aspect of the auricle, including the tragus.
- Branches of the facial nerve (cranial nerve VII) provide some motor innervation to the small intrinsic muscles of the auricle.
Muscles
The auricle contains both intrinsic and extrinsic muscles. These muscles are generally vestigial in humans, meaning they have lost much of their original function. The intrinsic muscles (such as the helicis major and helicis minor) lie entirely within the auricle and are attached to the cartilage. The extrinsic muscles (such as the auricularis anterior, superior, and posterior) are connected to the scalp and help minimally move the auricle.
Ligaments
The auricle is connected to the surrounding structures by several ligaments. The intrinsic ligaments help maintain the shape of the auricular cartilage, while the extrinsic ligaments connect the auricle to the temporal bone of the skull, anchoring it in place.
Adjacent Structures
The auricle is located on the lateral side of the head and is adjacent to the external auditory canal. It also lies close to the temporal bone, which forms the bony framework of the head behind the ear. The surrounding skin and scalp cover the rest of the cranial region where the auricle is attached.
Function
Sound Collection and Amplification
The primary function of the auricle is to collect sound waves from the surrounding environment and direct them into the external auditory canal. Its distinctive shape, with multiple ridges and depressions, helps to funnel sound waves more effectively toward the ear canal. The conical form of the auricle acts like a natural sound collector, capturing sound energy and focusing it toward the external acoustic meatus, which leads to the eardrum.
While this role is more pronounced in animals with mobile and larger auricles, in humans, it still assists in amplifying high-frequency sounds. The auricle is especially important in capturing sounds from the front and sides, which can enhance the listener’s ability to detect environmental sounds.
Sound Localization
One of the auricle’s key functions is assisting in sound localization, the process by which the brain determines the direction from which a sound is coming. The auricle’s complex shape, with features like the helix, antihelix, tragus, and concha, plays a role in filtering sound frequencies. This filtering creates subtle differences in the timing and intensity of sound waves reaching the eardrum depending on their origin.
These differences help the brain distinguish whether a sound is coming from above, below, in front, or behind the listener. For example, sounds coming from behind or below may reflect off the auricle in a way that changes the frequency content, providing cues to the brain about the sound’s direction.
Protection of the Ear Canal
The auricle helps to protect the external auditory canal from foreign objects and debris. Its structure, particularly the tragus and antihelix, partially shields the ear canal from direct exposure to external elements, reducing the likelihood of foreign objects, dirt, or water entering the canal.
In addition to its physical shielding, the auricle also plays a role in trapping larger particles or insects that might otherwise enter the ear canal. The tragus, with its flap-like shape, helps block direct access to the canal, while the ridges and depressions of the auricle can act as barriers to unwanted materials.
Aesthetic and Social Function
Though not a functional role related to hearing, the auricle has aesthetic and social significance. The shape and size of the auricle contribute to the overall appearance of the face and head. Variations in ear shape are often culturally significant, and ear piercings or modifications have been practiced by various cultures throughout history.
In many individuals, the auricle plays a key role in personal identification and social expression, from ear jewelry to the surgical reshaping of the ear (otoplasty). This function is not related to hearing but is an important aspect of the auricle’s role in human life.
Minor Role in Temperature Regulation
The auricle, particularly the lobule (earlobe), is rich in blood vessels and plays a minor role in temperature regulation. Although this is not a primary function, the increased blood flow to the lobule during cold conditions helps maintain warmth in this exposed area. In response to extreme cold, blood vessels may constrict to conserve heat, while in warm conditions, they may dilate to release heat.
This vascular function is more of a secondary effect, but it helps protect the sensitive skin and cartilage of the auricle from damage due to extreme temperatures.
Limited Role in Auricular Movement
The auricle has several intrinsic and extrinsic muscles, which theoretically allow for minor movements. While in many animals, these muscles enable the ear to swivel or move in response to sound, humans have lost most of this ability. The auricular muscles, including the auricularis anterior, superior, and posterior, can cause very subtle movements in some people, but these movements have no significant functional impact on hearing.
Clinical Significance
The auricle has important clinical significance in several areas, particularly in relation to trauma, congenital deformities, infections, and cosmetic concerns:
- Trauma and Injury: The auricle is susceptible to injuries such as lacerations, contusions, and fractures due to its exposed position. Conditions like auricular hematoma (commonly seen in wrestlers and boxers) can occur when blood accumulates between the cartilage and skin, potentially leading to deformity (cauliflower ear) if not treated promptly. Burns, frostbite, and other injuries can also affect the auricle’s structure.
- Congenital Deformities: Malformations of the auricle, such as microtia (underdeveloped auricle) or anotia (absence of the auricle), can occur congenitally, affecting both the aesthetic appearance and auditory function. These conditions often require reconstructive surgery to improve appearance and, in some cases, assist with hearing.
- Infections: The auricle can be affected by infections such as perichondritis, which involves inflammation of the cartilage, usually caused by trauma or piercing. Infections can lead to severe pain, swelling, and potential damage to the cartilage if untreated.
- Cosmetic and Reconstructive Surgery: Otoplasty, a common cosmetic procedure, is used to reshape or reposition the auricle for aesthetic reasons, often in individuals with prominent ears. In addition, reconstructive surgery may be necessary for individuals who have suffered traumatic injury or congenital defects.
