The history of the hearing aid before the ear trumpet, which was developed in the 1800’s is sketchy, but it is certain that shells and bones and other natural materials would have been employed in an attempt to amplify sounds.
The human ear, like that of other mammals, contains sense organs, has two separate and distinct functions, - that of hearing, and of postural equilibrium and the coordination of head and eye movements.
The outer ear consists of the visible part the pinna, or the auricle, and the short external auditory canal, the inner end of which is closed by the tympanic membrane, more commonly referred to as the eardrum, which has three layers. The outer layer is the delicate skin of the ear canal. The centre layer of the eardrum vibrates with the sound collected by the outer ear. The inside layer is a membrane that continues inside the middle ear. The inner layer continues to grow, and it can heal itself if it suffers a trauma that tears or punctures it. When a loud sound strikes the eardrum, the eardrum vibrates with tremendous force, and this force is itself sufficient to tear the eardrum.
The middle ear begins at the eardrum, which is like the head of a drum and it vibrates in response to sound. The middle ear itself is a narrow, cavity within the temporal bone, which is filled with air, which is why we say punctured eardrum. A chain of three tiny bones, the malleus or hammer, the incus, or the anvil, and the stapes or stirrup spans it. The middle ear also helps balance the pressure on the inside of the eardrum, which protects it from injury, the Eustachian tube connects to the back of the throat and acts as a pressure valve. The ossicular chain conducts sound from the tympanic membrane to the inner ear, the labyrinth. This is a complicated system of fluid filled passages and cavities located within the temporal bone.
The inner ear consists of two units, the vestibular apparatus, consisting of the vestibule and semicircular canals; these contain the sensory organs of postural equilibrium, more commonly known as balance. The second unit is the snail shell like cochlea, the organ of Corti lies within the middle chamber of the cochlea, which contains the sensory organ of hearing. These sensory organs are highly specialized endings of the eighth cranial nerve.
Three small loops located behind the cochlea are called semicircular canals. They, too, are filled with liquid and lined with hairs. They help you to keep your balance. Each time you move, the moving liquid and the movement of the hairs tell your brain what position your head is in. The brain then tells your body which muscles to move to help keep you upright. Your eyes tell your brain that you have stopped twirling around, but the liquid in your ears keeps moving. This means two conflicting signals the eyes tell the brain you have stopped, but the liquid in the ear tells the brain that you are still in motion. The resultant confusion is dizziness and that will prevail until the brain gets one clear message.
Special glands in the skin of the outer ear canal produce cerumen or earwax which is a sticky substance designed to prevent the skin of the outer ear canal from becoming dry and scaly. It also traps dirt and discourages insects from entering the ear. When the wax becomes dry, it flakes off, and leaves the ear taking the dust, dirt and any dead skin cells with it. Then the cycle begins again and more clean wax is produced.