The ear or the hearing apparatus in the human being consists of three distinct regions. They are:
The Outer Ear: This consists of the pinna or the “ear” that we are able to see on the sides of our head . This question-mark shaped organ made of soft tissue collects sound vibration from the surroundings.
These sound waves are ferried through the ear canal which also forms part of the outer ear. The ear canal contains glands that secrete wax. The walls of the ear canal are lined with hair that prevent foreign bodies entering the ear. The ear canal ends at the tympanum or eardrum.
Functions: It protects the delicate inner parts of the hearing mechanism. It collects and funnels sound waves into the ear. It helps in the judgment of direction and distance of sounds.
The Middle Ear: The eardrum and the three tiny bones or ossicles beyond it form the middle ear. This is an air filled chamber. The ossicles function like a hammer(malleus), anvil (incus) and stirrup (stapes) in co ordination. The stapes is attached to a foot plate which is in direct contact with the fluid of the inner ear.When airwaves hit the ear drum the ossicles move, corresponding to the kind of vibration received and this pattern is received by the footplate. The footplate communicates the pattern to the inner ear.
Functions:It transmits and amplifies sound waves from tympanic membrane to the stapes footplate converting energy from air medium to a fluid medium of the inner ear.
The Inner Ear: This is a fluid filled labyrinth consisting of the vestibule, the cochlea and the semicircular canals. Of these the snail shaped cochlea is the part concerned with hearing.
The cochlea is a bony structure filled with fluid. There are sensory receptors inside the cochlea which holds the hair cells, the nerve receptors for hearing. The mechanical energy of the middle ear hits the cochlea and moves the fluid in it. This stimulates the hair cells. Signals from these hair cells are translated into nerve impulses. The nerve impulses are transmitted to the brain by the cochlear portion of the acoustic nerve.
From the ear the cochlear nerve carries the auditory signals to the brain. The part of the brain that receives these signals is called the auditory cortex. From each ear auditory signals are conveyed to both sides(hemispheres of the brain). This way what is heard by the left ear is conveyed to the right side of the brain and also to the left side.
We make sense of what we hear because the Central auditory complex in the brain process the impulses conveyed to it. It helps us to understand the pattern of the sounds, place the sound in time and place, adjust our hearing