HUMAN EAR: OUTER EAR, MIDDLE EAR, INNER EAR, HEARING

The ear is the organ of hearing and balance in mammals.

Human Ear has receptors that are sensitive to the audible frequency range. The audible frequency range for a human ear is 20Hz – 20,000Hz. Human ear is deaf to vibrations which are below 20Hz or above 20,000Hz. This is the ideal range, but exact audible frequency range differs for each person. A young person may listen as low as 20Hz, but an old man may not. Age factor has lots of importance in the audible frequency range for a person. 

Structure of Human Ear:

Human ear consists of three parts.

• Outer Ear
• Middle Ear
• Inner Ear

Outer Ear:

Outer ear is the outer part of the ear which is visible to us. This visible part is made up of cartilage confined by the skin known as the Ear pinna. Many vertebrates, like eyes, can move their pinna in order to focus on vibrations. Opening of the ear is a tube that leads inwards called the external auditory meatus. It has sebaceous organs that produce secretions. Ear tube collects sound energy and focuses it on the tympanic membrane (eardrum). The chief function of the outer ear is to direct sound waves toward the tympanic membrane. Outer ear also contains muscles which have little activity in humans as many mammals can move their ear to focus sound waves.

Middle Ear:

Middle ear is the part of the ear next to eardrum. Middle ear is an air filled pit which communicates with the nasal cavity (pit of nose) by a thin tube called Eustachian tube which allows the pressure to level between middle ear and throat. There are three bones in the middle ear known as incus, malleus and stapes that fits into the window-like opening in the bone of the brain that differentiates the middle ear from the internal ear. These three bones transmit the sound vibrations from the tympanic membrane (eardrum) into the inner ear. The chief function of the middle ear is to transmit sound waves from the tympanic membrane to the inner ear. Like outer ear, inner ear also has muscles and nerves.

Inner Ear:

Inner ear is the inner most part of ear. It is primarily concerned with detection of sound and balancing. The internal ear comprises the following parts. There are 3 semicircular channels having inflammation at one of their closures called the ampullae. These semicircular channels open into utricles, sacculus and a twisted cochlea.  

The auditory nerve which is originating from brain supplies many branches to the cochlea making its inward cells delicate to sound vibrations.  The three semicircular channel, utricles, sacculus and cochlea are jointly referred to as membranous labyrinth. The membranous labyrinth runs within the bony labyrinth. A fluid called perilymph is present between them and inside it, is an alternate liquid the endolymph containing certain calcareous particles.

Hearing:

The sound vibrations circulating in the atmosphere are directed into the external auditory meatus. These vibrations strike the tympanic membrane (eardrum) and make it to vibrate. The tympanic membrane transmits the vibrations to the three ossicles and then to the perilymph and the endolymph. The calcareous particles in the endolymph hit the responsive cells of the cochlea which is stimulated and sends impulses that go through the auditory nerve to mind and are deciphered as sound.

Balancing:

The membranous labyrinth (3 semicircular channels, utricles, sacculus and coiled cochlea) excluding cochlea have to do with balancing and posture. Any flaw in these causes wooziness. It is a basic experience that if an individual goes all around on a swing, he loses his balance and is not able to stand upright for quite a while until the balance is reinstated.