Hearing is one of the five senses. It is a complex process of picking up sound and attaching meaning to it. The ability to hear is critical to understanding the world around us.
The human ear is a fully developed part of our bodies at birth and responds to sounds that are very faint as well as sounds that are very loud. Even before birth, infants respond to sound.
So, how do we hear?
The ear can be divided into three parts leading up to the brain – the outer ear, middle ear and the inner ear.
- The outer ear consists of the ear canal and eardrum. Sound travels down the ear canal, striking the eardrum and causing it to move or vibrate.
- The middle ear is a space behind the eardrum that contains three small bones called ossicles. This chain of tiny bones is connected to the eardrum at one end and to an opening to the inner ear at the other end. Vibrations from the eardrum cause the ossicles to vibrate which, in turn, creates movement of the fluid in the inner ear.
- Movement of the fluid in the inner ear, or cochlea, causes changes in tiny structures called hair cells. This movement of the hair cells sends electric signals from the inner ear up the auditory nerve (also known as the hearing nerve) to the brain.
The brain then interprets these electrical signals as sound and that’s how we hear.
The outer ear consists of the pinna, or auricle, and the ear canal (external auditory meatus). The pinna – the part of the “ear” that we see on each side of our heads – is made of cartilage and soft tissue so that it keeps a particular shape but is also flexible. The pinna serves as a collector of sound vibrations around us and guides the vibrations into the ear canal. It helps us decide the direction and source of sound.
The middle ear begins with the eardrum at the end of the ear canal. The middle ear contains three tiny bones, called the ossicles. These three bones form a connection from the eardrum to the inner ear. As sound waves hit the eardrum, the eardrum moves back and forth causing the ossicles to move. As a result, the sound wave is changed to a mechanical vibration.
The inner ear contains the sensory organs for hearing and balance. The cochlea is the hearing part of the inner ear. The semicircular canals in the inner ear are part of our balance system.
The cochlea is a bony structure shaped like a snail and filled with two fluids (endolymph and perilymph). The Organ of Corti is the sensory receptor inside the cochlea which holds the hair cells, the nerve receptors for hearing.
The mechanical energy from movement of the middle ear bones pushes in a membrane (the oval window) in the cochlea. This force moves the cochlea’s fluids that, in turn, stimulate tiny hair cells. Individual hair cells respond to specific sound frequencies (pitches) so that, depending on the pitch of the sound, only certain hair cells are stimulated.
Signals from these hair cells are changed into nerve impulses. The nerve impulses are sent out to the brain by the cochlear portion of the auditory nerve. The auditory nerve carries impulses from the cochlea to a relay station in the mid-brain, the cochlear nucleus. These nerve impulses are then carried on to other brain pathways that end in the auditory cortex (hearing part) of the brain.
Also housed within the inner ear are the semicircular canals, the utricle, and the saccule. These structures help control one’s sense of steadiness or balance. These balance organs share the temporal bone space with the cochlea. These organs also share the same fluid that is in the cochlea.
Wondering weather or not your ear health is where it should be? Dr. Emily McMahan, Audiologist can answer any or all of your questions.
Schedule Now 907.522-4357 email@example.com