The Basics of Hearing: How Our Ears Capture Sound
When we think about ears and hearing, we often think about the external part of the ear that can be easily seen. While this part of the ear plays an important role in hearing, most of the process that allows us to hear occurs further inside the head. At Knox Audiology, ears are our focus, and we recognise how amazing ears are in the way they capture sound and turn it into hearing. So, we have put together this blog to tell you more about how we hear.
The first part of the ear in the hearing process is the outer ear. The outer ear – called the pinna – collects sounds and directs them into the ear canal. All those little bumps and crevices on the outside of the ear help this to happen. This function of the outer ear in directing sounds further into the ear contributes to why you hear better from in front of you, than behind.
Once the sound is collected by the pinna, it is sent down the ear canal. At the end of the ear canal is the eardrum – called the tympanic membrane – which vibrates when the sounds hit it. It vibrates differently depending on the frequency (pitch) and volume of the sound. Attached to the tympanic membrane is the head of one of three small bones in the middle ear. These bones, the smallest in the body, are called the malleus, incus, and stapes. Sometimes, they are referred to as the hammer, anvil, and stirrup. The middle ear, which includes the tympanic membrane and the three little bones, not only continues to transmit the sound along the hearing pathway, to the inner ear, it also serves an important role in amplifying sounds so the inner ear can make use of the information it receives. The last of the three little bones, the stapes, connects to the oval window. It pushes on the oval window which is the start of the cochlea in the inner ear.
The cochlea is snail shell shaped organ. It is filled with fluid, and several tiny structures, which are critical for turning the sound waves into nerve impulses the brain can understand so we can hear. When the oval window moves, it displaces the fluid (causes waves) in the cochlear. The fluid is displaced maximally (i.e. a bigger wave occurs) in different parts of the cochlear depending on the pitch of the sound. The sound causes a bigger wave at the beginning of the cochlea if it is a sharp, high-pitched, tinny sound. However, it causes a bigger wave further in towards the middle of the snail shell shaped cochlea if it is a deep, low-pitched sound.
As the fluid moves in the inner ear, it causes another membrane, called the basilar membrane to shift. As this membrane shifts, it activates tiny little cells in the ear called hair cells. When activated, these hair cells trigger nerve impulses to be generated that then travel along the hearing nerve to give the brain information about the sounds you are hearing. The brain then processes the nerve impulses to make sense of the information. While this all sounds like a long pathway, it occurs really quickly! It is so quick that you don’t notice any delay when you are talking to someone.
While ears are complicated, they mostly do a good job of working well. However, sometimes something will stop working as well as it should in the ear. This can affect any part of the ear, the outer ear, the middle ear, or the inner ear. If this happens you may notice you don’t hear as well as you used to. You may also notice noises in your ears (tinnitus), trouble with your balance, discomfort, or other odd sensations such as a blocked or full sensation in your ears. If you feel you, or your child, are not hearing well, or something seems to be affecting the ears, the best place to start is with a hearing assessment. At Knox Audiology, our university-trained audiologists can complete a comprehensive assessment, and guide you as to what the next steps should be depending on the results they find.