We may detect sounds with our ears, but we process and interpret what we are hearing with our brain! An understanding of how sound travels to the brain is important in understanding the different types of hearing loss and their causes.
The 3 Parts of the Ear
Sound must first travel through all three parts of the ear before it reaches the brain.
01. The Outer Ear
is comprised of the pinna, the ear canal, and the eardrum. The pinna serves to collect, localize, lead, and enhance sounds. The ear canal is an irregularly shaped and curved tube approximately 25 mm in length and 8 mm in diameter. The shape of the ear canal helps prevent water and other foreign materials from collecting inside. The ear canal ends at the eardrum, a thin layer of skin, which separates the outer ear from the middle ear.
02. The Middle Ear
is comprised of the three tinniest bones in the human body known as the ossicles: the malleus, incus, and stapes. The eustachian tube is also located in the middle ear which links the middle ear to the nasopharynx. The eustachian tube equalizes air pressure in the middle ear space allowing the eardrum to move freely as soundwaves enter through the ear canal.
03. The Inner Ear
is comprised of the cochlea, semicircular canals, and the vestibule. The cochlea is the organ of hearing where sound waves are converted into electrical signals. The semicircular canals assist with our sense of balance, posture, and equilibrium. The vestibule is the area that lies between the cochlea and the semicircular canals, also contributing to our sense of equilibrium.
How Sound Travels from Our Ears to Our Brain
Sound waves are collected by the pinna of the outer ear and are funnelled into the ear canal. The sound waves travel to the eardrum causing it to vibrate which in turn causes movement of the three ossicles, the malleus, incus, and stapes inside the middle ear. Movement of the stapes moves fluid inside the cochlea in the inner ear causing hair cells to move back and forth. This movement sends electrical impulses up the auditory nerve and to the brain where sounds are interpreted.