THE HUMAN EAR

The ear is an advanced and very sensitive organ of the human body.  The function of ear is to detect, transmit and transduce sound . Structurally, an ear is divided into three major sections i.e,. the outer ear, the middle ear, the inner ear.

THE OUTER EAR (EXTERNAL EAR)

The Outer ear or external ear is further divided into following parts:

• AURICLE (PINNA) – It is the visible part of the ear. It collects vibrations in the air that produces sound.
• EXTERNAL AUDITORY MAETUS– It leads inwards and extends up to the tympanic membrane (ear drum). It is lined with stratified epithelium and wax glands.

• TYMPANIC MEMBRANE (EAR DRUM) – It is the thin layer of tissue in the human ear that receives sound vibrations from the outer air and transmits them to the auditory ossicles, which are tiny bones in the tympanic cavity. This membrane separates the middle ear and the external ear.

THE MIDDLE EAR

The middle ear is further divided into following parts:

1. TYMPANIC CAVITY– It is a small cavity surrounding the bones of the middle ear. The tympanic cavity has an auditory tube known as the Eustachian tube.
2. EUSTACHIAN TUBE– It is a canal that connects the middle ear to the Nasopharynx, which consists of the upper throat and the back of nasal cavity. It controls the pressure within the middle ear, making it equal to the air pressure outside the body.
3. EAR OSSICLES– They are also known as auditory ossicles. These are responsible for transmitting sound waves from the eardrum to the middle ear. The absence of the auditory ossicles would constitute a moderate-to-severe hearing loss. There are three ossicles in the human ear:-

1. Malleus(Hammer)– It is a hammer-shaped small bone which connects with the incus and is attached to the inner surface of the eardrum. It transmits the sound vibrations from the eardrum to the incus.

2. Incus(Anvil)– The anvil-shaped small bone receives vibrations from the malleus, to which it is connected, and transmits these to the stapes.

3. Stapes(Stirrup)– It is a stirrup-shaped bone, and the smallest in the human body. It rests on the oval window, to which it is connected by an annular ligament.

THE INNER EAR (INTERNAL EAR)

The inner ear is further divided into following parts:

• BONY LABYRINTH– It is the rigid, bony outer wall of the inner ear in the temporal bone. It consists of three parts: the vestibule, semicircular canals, and cochlea. They contain a clear fluid, the perilymph, in which the membranous labyrinth is situated.
• MEMBRANOUS LABYRINTH– It is a system of ducts and dilatations located within the bony labyrinth of the internal ear and it contains the receptors for hearing and balance. It is composed of two functional parts: the vestibular labyrinth and the cochlear labyrinth.

MECHANISM OF HEARING

• The sound wave pass through the auditory canal and reaches the eardrum.
• The vibrations produced pass through the tympanic membrane to the Tympanic cavity.
• The ear ossicles in the tympanic cavity receives the vibrations and the stapes pushes the oval window in and out.
• This action is passed on to the organ of corti, the receptor of hearing, that contains tiny hair cells that translate the vibrations into electrical impulse that are transmitted to the brain by sensory nerves.

POINTS TO REMEMBER

• The Eustachian tube equalizes the air pressure in the middle ear and maintains the balance.
• The Vestibular complex contains receptors that maintain body balance.
• Abnormalities in internal ear may cause deafness.
• Ear infections are more common in children than adults because of their developing immune system and differences between their Eustachian tube.