Ear

The human ear is the anatomical structure responsible for hearing and balance.

The ear consists of three parts: the outer, middle, and inner ears. The outer ear collects sounds from the environment and funnels them through the auditory system. The outer ear is composed of three parts. The pinnas, the two flap-like structures on either side of the head commonly called ears, are skin-covered cartilage, not bone, and are therefore flexible. The second part of the outer ear, the external auditory canal, is a passageway in the temporal lobe of the skull, which leads from the outside of the head and extends inward and slightly upwards. In the adult human, it is lined with skin and hairs and is approximately 1 in (2.5 cm) long.

The third part of the outer ear, the tympanic membrane or eardrum, is a thin, concave membrane stretched across the inner end of the external auditory canal much like the skin covering the top of a drum. The eardrum marks the border between the outer ear and middle ear. The eardrum transmits sound to the middle ear by vibrating in response to sounds traveling down the external auditory canal. The middle point of the tympanic membrane is attached to the stirrup, the first of three bones contained within the middle ear.

The middle ear transmits sound from the outer ear to the inner ear and is the site of one of the most common infections in infants and young children, otitis media. The middle ear consists of an oval, air-filled space approximately 2 cubic cm in volume. The tympanic membrane is on one end and the back wall, separating the middle ear from the inner ear, has two windows, the oval window and the round window. The eustachian tube connects on one side, the brain lies above, and the jugular vein lies below. The middle ear is lined entirely with mucous membrane (similar to the nose) and is surrounded by the bones of the skull.

The eustachian tube connects the middle ear to the nasal passage. This tube is normally closed, opening only as a result of muscle movement during yawning, sneezing, or swallowing. The eustachian tube allows for air pressure equalization, permitting the air pressure in the middle ear to match the air pressure in the outer ear. The most noticeable example of eustachian tube function occurs when there is a quick change in altitude, such as when a plane takes off. Prior to takeoff, the pressure in the outer ear is equal to the pressure in the middle ear. When the plane gains altitude, the air pressure in the outer ear decreases, while the pressure in the middle ear remains the same, causing the ear to feel "plugged." In response to this the ear may "pop." The popping sensation is actually the quick opening and closing of the eustachian tube, and the equalization of pressure between the outer and middle ear.

Three tiny bones, the hammer (malleus), the anvil (incus), and the stirrup (stapes), conduct sound waves from the outer ear to the inner ear, which is responsible for interpreting and transmitting sound sensations and balance sensations to the brain. The inner ear is small (about the size of a pea) and complex in shape, and its series of winding interconnected chambers has been compared with (and called) a labyrinth.

Otitis media—the common ear infection—occurs when bacteria or viruses invade the middle ear through the eustachian tube and cause a swollen or inflamed eardrum. It is estimated that at least 60% of infants experience at least one ear infection before their first birthday, and 70% by the age of two. At least half of these children will have three or more. Most children outgrow their susceptibility to ear infections by the age of five as their bodies grow and their immune systems become more able to handle viruses.

Parents suspect ear infection when infants become irritable, possibly run a fever, and tug at their ears. Usually very painful, otitis media is responsible for at least 30% of visits to pediatricians each year. Diagnosis is often difficult because of the small size of children's ears. Treatment typically has consisted of antibiotics, although there has been much disagreement in recent years about their effectiveness. Some studies suggest that many cases of otitis media resolve themselves without treatment, particularly those caused by viruses. Many pediatricians contend that overdispensing antibiotics has reduced their effectiveness as bacteria develop resistance to them.

A more serious type of ear infection, otitis media with effusion (OME), occurs when fluid accumulates to block the eardrum. OME often causes no symptoms and, if left untreated for an extended period, can seriously compromise a child's ability to hear. Subsequent learning and language development may also be affected. Again, there are varying recommended treatments. Many doctors do not intervene in the early stages of OME, believing most cases resolve themselves within a few months. Antibiotics and surgery—to implant tubes that drain the fluid away from the eardrum—are other options. Some physicians theorize that frequent episodes of otitis media cause OME.

Permanent hearing loss is one possible consequence of ear infections in infants and children. While many are believed to originate with colds and upper respiratory infections that are difficult to prevent, there are some suggestions for reducing the incidence. First, some studies have shown that breastfeeding during the first 4-6 months of life dramatically reduces the number of ear infections. Breastfed babies often are fed in a more upright position than bottle-fed babies, which may prevent fluid from escaping into the ear and providing a breeding ground for bacteria. It is also believed that mothers transmit certain antibodies that help babies combat infection—causing bacteria. Parents are also advised to reduce infants' exposure to environmental risks, such as secondhand cigarette smoke, which may increase the incidence of ear infections. Frequent close contact with other children, such as in group day care situations, may also increase the likelihood of contracting ear infections.

Hearing loss in infants and children can result from other factors as well, particularly noise exposure. Loud music heard through earphones is a particular concern for adolescents. Toys such as video games and walkie/talkies present risks for children of all ages. It is recommended that infants be tested for hearing impairment before they are discharged from the hospital after birth, and definitely within the first six months of life. Low birth weight, use of a ventilator after birth, and family history of hearing loss are all considered potential risk factors.

Ear

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