How Hearing Works
Hearing is an important sense to your everyday life. From alarms to important conversations throughout the day, our sense of hearing is critical to the process of communicating information.
The way the auditory system works is incredibly complex, and requires a number of functions to work and hear properly.
Functions of the Ear
1) Sound is transmitted through the air as sound waves from the environment. The sound waves are gathered by the outer ear and sent down the ear canal to the eardrum.
2) The Sound waves cause the eardrum to vibrate, which sets the three tiny bones in the middle ear into motion.
3) The motion of the three bones causes the fluid in the inner ear to move.
4) The movement of the fluid in the inner ear causes the hair cells in the cochlea to bend. The hair cells change the movement into electrical impulses.
5) These electrical impulses are transmitted to the hearing (auditory) nerve and up to the brain, where they are interrupted as sound.
The Outer Ear
The visible part of the outer ear is called the pinna, or auricle. The pinna, with its grooves and ridges, along with the ear canal provide a natural volume boost for sounds in the 2000-3000 Hz frequency range, where we perceive many consonant sounds of speech.
The ear canal, also called the external auditory meatus, is the other important component of the outer ear. The ear canal is lined with only a few layers of skin and fine hair, and is a highly vascularized area. This means that there is an abundant flow of blood to the ear canal. Wax (Cerumen) accumulates in the ear canal and serves as a protective barrier to the skin from bacteria and moisture. Earwax is normal and varies in amount based per person. It only becomes problematic if it completely blocks the ear canal.
The Middle Ear
The eardrum, or Tympanic Membrane (TM), is the dividing structure between the outer and middle ear. Although it is an extremely thin membrane, the eardrum is made up of three layers to increase its strength.
The Ossicles are three tiny bones of the middle ear located directly behind the tympanic membrane. These three bones form a connected chain in the middle ear. The Ossicles take mechanical vibrations received at the tympanic membrane, increase the strength of these vibrations and transmit them into the inner ear.
The Eustachian tube is the middle ear’s air pressure equalizing system. The middle ear is encased in bone and does not associate with outside air except through the Eustachian tube. This tubular structure is normally closed, but it can be involuntarily opened by swallowing, yawning or chewing. It can also be intentionally opened to equalized pressure in the ears, like when flying in an airplane. When this happens, you might hear a soft popping sound.
The Inner Ear
The inner ear is an organ located deep within the temporal bone (the bone of the skull on both sides of the head above and to the side of the outer ear). The inner ear has two main structures: the semicircular canals and the cochlea.
The semicircular canals are three tiny, fluid-filled tubes in your inner ear that help you keep your balance. When your head moves around, the liquid inside the semicircular canals sloshes around and moves the tiny hairs that line each canal. These hairs translate the movement of the liquid into nerve messages that are sent to your brain. Your brain then can tell your body how to stay balanced. If you spin around and then stop, the liquid inside your semicircular canals moves awhile longer and the hairs continue to send the message that you are spinning even though you’re not.
The function of the cochlea is to transform the vibrations of the cochlear liquids and associated structures into a neural signal. This occurs at the organ of Corti, which is located all along the cochlea. It is composed of sensory cells called hair cells, which convert vibrations into neural messages. These messages are then passed to the auditory nerve and carried up to the brain.
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