functions of the ears
The set of ears placed on either side of the head is a sensitive organ that collects the sound waves present and converts those waves of sound into an impulse by the auditory nerve that the brain understands. The vestibular system helps to maintain an equilibrium balance between bodily motions with the environment. Ears are also essential for the head and eye movements in response to the source of action. The internal and external auditory receptor cells provide the necessary functions of hearing and balancing. The most vital function of hearing takes place when the vibrations from the external source are captured by the eardrum that enters the tympanic membrane and then to the membranous labyrinth. In this process, the three small bones-the malleus, stapes, and incus are essential for causing vibrations in the basilar membrane. The fluid inside the semicircular canals sits erect at an angle of 90 degrees, hence sudden body changes cause the fluid inside to move, which sends a signal to the receptors that stabilize the equilibrium. In the fetus stage, the complete development of the auditory cortex takes place, due to which the hearing ability of a newborn is practical. The three sections are the external consisting of the pinna, the external auditory meatus, and the tympanic membrane; the middle includes ear ossicles and eustachian tubes, and the internal ear has a cochlea, membranous labyrinth, and the auditory nerve.
The ear development starts as early as the sixth week of pregnancy. The average human ear is about 2.4 inches long, the ear lobe being 0.74 inches long and 0.77 in width.
The three parts of the ear are as follows:
1) The external ear:
Auricle or Pinna: Unlike any other mammals, the human ear is immobile. Sound waves primarily move over the funnel-shaped curves in the auricle before entering the ear canal. External Auditory Meatus: The walls contain cartilage and temporal bone and are sigmoid in shape.
Tympanic membrane: The tympanic membrane acts as a barrier between the external and middle ear.
2) The middle ear:
Ear ossicles: The malleus, stapes, and incus that help to transmit the sound vibrations to the cochlea.
The eustachian tube connects the middle ear with the nasopharynx and is 4 cm long.
3) The inner ear:
4) Cochlea: Snail-shaped membrane lined with small hair that sends an electrical impulse to the brain.
5) Membranous labyrinth: The semicircular canals are filled with endolymph and include the cochlear duct, saccule, and utricle.
6) The auditory nerve: It sends the electrical impulse in the brain.
Functions of the ear
The human hearing frequency range is between 20kilo Hertz (kHz) and 20kHz or 10 octaves. However, with the increasing age, the sensitivity diminishes. The following are the salient functions ears carry out:
1) Localize the position: The pinna blocks some higher frequency and helps to identify the source of the sound.
2) Amplification: The ear canal also functions as amplifying the frequency between 3000 and 4000 Hz.
3) Loudness recruitment: The Eustachian tube functions as a pressure-equalizer during a sudden high-altitude difference due to the blocked ear; it produces negative pressure by absorbing carbon dioxide and oxygen in the middle ear. The mastoid air cells function as an air reservoir for the pressure change. The inner hair cells get stimulated quickly with the rapid increase in sound to protect the eardrums.
4) Protection from hearing loss: The outer hair cells are not as strong as the inner hair cells, and therefore the increase of toxic substances in the ear, aging, listening to loud music, hearing loss takes place but does not cause permanent deafness.
5) Decreasing sound vibrations: In cases of loud noises, the malleus and stapes function as protection by decreasing the number of vibrations and protecting the cochlea.
6) Mood changes: Sounds have certain stimuli; some work as a mood enhancer by calming down, producing stress, or a feeling of anger.
7) The direction of head movement: The change in orientation located in the membranous labyrinth is responsible for the direction of the head movement.
8) Prevention of bacteria: External auditory meatus has wax glands present that prevent any object from entering inside.
Clinical disorders of the ear functions
Ears play a significant role in the hearing process. There are certain factors that contribute to disrupted and impaired hearing or hearing loss. They are as follows:
1) Inflammation: The most common ear inflammations are saprophytic bacteria causing allergies, eczema, otitis externa, serous otitis media.
2) Cholesteatoma: Due to the infection of the middle ear with the defective function of the Eustachian tube
3) Microtia: The failure of development of a complete ear causes this congenital disease.
4) Treacher Collins syndrome: A condition in which it shows ossicular abnormalities and deformed hearing.
5) Crouzon syndrome: Around 30 – 50% of hearing difficulties occur due to premature fusion of fibrous joints.
6) Meniere’s disease: Due to allergies or other factors, the fluid present in the middle ear gets affected, causing vertigo and, in some conditions, a permanent hearing loss.
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