The outer ear, external ear, or auris externa is the external part of the ear, which consists of the auricle (also pinna) and the

ear canal The ear canal (external acoustic meatus, external auditory meatus, EAM) is a pathway running from the outer ear to the middle ear. The adult human ear canal extends from the auricle to the eardrum and is about in length and in diameter. S ...

. It gathers sound energy and focuses it on the eardrum ( tympanic membrane).

Structure

Auricle

The visible part is called the auricle, also known as the pinna, especially in other animals. It is composed of a thin plate of yellow elastic cartilage, covered with integument, and connected to the surrounding parts by ligaments and muscles; and to the commencement of the

by fibrous tissue. Many

mammal A mammal () is a vertebrate animal of the Class (biology), class Mammalia (). Mammals are characterised by the presence of milk-producing mammary glands for feeding their young, a broad neocortex region of the brain, fur or hair, and three ...

s can move the pinna (with the auriculares muscles) in order to focus their hearing in a certain direction in much the same way that they can turn their eyes. Most humans do not have this ability.

Ear canal

From the pinna, the

sound wave In physics, sound is a vibration that propagates as an acoustic wave through a transmission medium such as a gas, liquid or solid. In human physiology and psychology, sound is the ''reception'' of such waves and their ''perception'' by the ...

s move into the

(also known as the ''external acoustic meatus'') a simple tube running through to the

middle ear The middle ear is the portion of the ear medial to the eardrum, and distal to the oval window of the cochlea (of the inner ear). The mammalian middle ear contains three ossicles (malleus, incus, and stapes), which transfer the vibrations ...

. This tube leads inward from the bottom of the auricula and conducts the vibrations to the tympanic cavity and amplifies frequencies in the range 2 kHz to 5 kHz.

Auricular muscles

Intrinsic muscles

The intrinsic auricular muscles are: * The helicis major is a narrow vertical band situated upon the anterior margin of the helix. It arises below, from the spina helicis, and is inserted into the anterior border of the helix, just where it is about to curve backward. * The helicis minor is an oblique fasciculus, covering the crus helicis. * The tragicus is a short, flattened vertical band on the lateral surface of the tragus. Also known as the mini lobe. * The antitragicus arises from the outer part of the antitragus, and is inserted into the cauda helicis and

antihelix The antihelix (anthelix) is a part of the visible ear; the pinna. The antihelix is a curved prominence of cartilage parallel with and in front of the helix on the pinna. The antihelix divides above into two ''legs'' or crura; the ''crura anti ...

. * The transverse muscle is placed on the cranial surface of the pinna. It consists of scattered fibers, partly tendinous and partly muscular, extending from the eminentia conchae to the prominence corresponding with the scapha. * The oblique muscle also on the cranial surface, consists of a few fibers extending from the upper and back part of the concha to the convexity immediately above it. The intrinsic muscles contribute to the topography of the auricle, while also function as a sphincter of the external auditory meatus. It has been suggested that during prenatal development in the womb, these muscles exert forces on the cartilage which in turn affects the shaping of the ear.

Extrinsic muscles

The extrinsic auricular muscles are the three

muscle Muscle is a soft tissue, one of the four basic types of animal tissue. There are three types of muscle tissue in vertebrates: skeletal muscle, cardiac muscle, and smooth muscle. Muscle tissue gives skeletal muscles the ability to muscle contra ...

s surrounding the '' auricula'' or outer ear: * anterior auricular muscle * superior auricular muscle * posterior auricular muscle The superior muscle is the largest of the three, followed by the posterior and the anterior. In some mammals these muscles can adjust the direction of the pinna. In humans these muscles possess very little action. The auricularis anterior draws the auricula forward and upward, the auricularis superior slightly raises it, and the auricularis posterior draws it backward. The superior auricular muscle also acts as a stabilizer of the occipitofrontalis muscle and as a weak brow lifter. The presence of auriculomotor activity in the posterior auricular muscle causes the muscle to contract and cause the pinna to be pulled backwards and flatten when exposed to sudden, surprising sounds.

Function

One consequence of the configuration of the outer ear is selectively to boost the

sound pressure Sound pressure or acoustic pressure is the local pressure deviation from the ambient (average or equilibrium) atmospheric pressure, caused by a sound wave. In air, sound pressure can be measured using a microphone, and in water with a hydrophon ...

30- to 100-fold for frequencies around 3&000p;kHz. This amplification makes humans most sensitive to frequencies in this range—and also explains why they are particularly prone to acoustical injury and hearing loss near this frequency. Most human speech sounds are also distributed in the bandwidth around 3 kHz.

Clinical significance

Malformations of the external ear can be a consequence of hereditary disease, or exposure to environmental factors such as

radiation In physics, radiation is the emission or transmission of energy in the form of waves or particles through space or a material medium. This includes: * ''electromagnetic radiation'' consisting of photons, such as radio waves, microwaves, infr ...

infection An infection is the invasion of tissue (biology), tissues by pathogens, their multiplication, and the reaction of host (biology), host tissues to the infectious agent and the toxins they produce. An infectious disease, also known as a transmis ...

. Such defects include: *A preauricular fistula, which is a long narrow tube, usually near the tragus. This can be inherited as an

autosomal recessive In genetics, dominance is the phenomenon of one variant (allele) of a gene on a chromosome masking or overriding the Phenotype, effect of a different variant of the same gene on Homologous chromosome, the other copy of the chromosome. The firs ...

fashion and may suffer from chronic infection in later life. * Cosmetic defects, such as very large ears, small ears. * Malformation that may lead to functional impairment, such as atresia of the external auditory meatus or aplasia of the pinna, * Genetic

syndrome A syndrome is a set of medical signs and symptoms which are correlated with each other and often associated with a particular disease or disorder. The word derives from the Greek language, Greek σύνδρομον, meaning "concurrence". When a sy ...

s, which include: ** Konigsmark syndrome, characterised by small ears and atresia of the external auditory canal, causing conductive hearing loss and inherited in an

manner. ** Goldenhar syndrome, a combination of developmental abnormalities affecting the ears, eyes, bones of the skull, and vertebrae, inherited in an

autosomal dominant In genetics, dominance is the phenomenon of one variant (allele) of a gene on a chromosome masking or overriding the Phenotype, effect of a different variant of the same gene on Homologous chromosome, the other copy of the chromosome. The firs ...

manner. ** Treacher Collins syndrome, characterised by dysplasia of the auricle, atresia of the bony part of the auditory canal, hypoplasia of the auditory ossicles and tympanic cavity, and 'mixed' deafness (both sensorineural and conductive), inherited in an autosomal dominant manner. ** Crouzon syndrome, characterised by bilateral atresia of the external auditory canal, inherited in an

manner.

Surgery

Usually, malformations are treated with surgery, although artificial prostheses are also sometimes used. *Preauricular fistulas are generally not treated unless chronically inflamed. *Cosmetic defects without functional impairment are generally repaired after ages 6–7. If malformations are accompanied by hearing loss amenable to correction, then the early use of hearing aids may prevent complete hearing loss.

Evolution

The outer ear's cartilage is homologous to the cartilage in gills of amphibians, fishes, and invertebrates such as the horseshoe crab. The extracolumella cartilage of reptiles is likely also homologous.