From the bellows of a tuba to the shrill voice of an opera singer, our ears catch it all. How do they accomplish such a feat? In my previous article, we answered the question: “What is sound?” While that is a surprisingly complex answer, we still have no idea how we perceive sound. Our ears are incredibly complex organs that rely almost completely on physical mechanisms. In this article we will be answering the question: How do we hear?
Labeled diagram of the human ear (Source)
The outer ear consists of the earlobe, eardrum, and ear canal. The earlobe, also known as the pinna, is shaped like a funnel so that it can catch sounds from every angle. The pinna is the only part of your auditory system that protrudes from your head. After a sound wave is funneled through the pinna, it enters the ear canal. The ear canal is a tube that connects the pinna to the eardrum and selectively amplifies certain sounds according to their frequencies. The selective amplification of sound waves helps our brains comprehend which direction sound is coming from. The eardrum is a thin flexible membrane that is spread across the end of the ear canal. When a sound wave hits the eardrum, it vibrates.
As the eardrum vibrates, it transfers its energy into the middle ear. The middle ear consists of 3 of the smallest bones in your body. These are the malleus (hammer), incus (anvil), and the stapes (stirrup). These bones are collectively known as the ossicles. The eardrum vibrates against the hammer, which hits the anvil, which vibrates against the stirrup. Ok, so what’s the point? Why do you need three different bones? Why not just one? As I stated in my last article, sound loses energy when changing mediums. To compensate for the loss of energy when sound passes from air into the eardrum, the bones in your middle ear amplify sound waves. But how do they do this? The ossicles are shaped like levers. So like any good levers, they help you out and amplify mechanical force, thus also amplifying sound.
The inner ear is the most delicate part of your auditory system. While damage to the outer or middle ear can be fixed, any damage to the inner ear is permanent (so don’t mess with it!). The inner ear consists of the oval window and the cochlea. The stirrup vibrates against the oval window. The oval window in turn transmits those vibrations into the cochlea, which is a small snail-shaped organ that is filled with fluid. Hairs lining the cochlea pick up on movement, converting mechanical motion into electrical signals, which are then transmitted up the auditory nerve into the temporal lobe of the brain. The temporal lobe compiles electrical signals into sound and is the end of the line for our hearing. Unlike many other sensory organs, there are very few cochlear hair cells; only 2,000 make up the entire cochlea. As the cochlea is one of the most precise instruments in the body, every hair cell is attached to a specific neuron, so it becomes nearly impossible for hair cells to regenerate without errors. Again, don’t mess with the inner ear!
Your hearing is the only sense that enables you to react to stimuli from any direction. Sight, smell, taste, and touch require either close contact or have a restricted field of view. Your hearing is a 24/7 surveillance system, active even while you sleep. Our ears are constantly at work. They are incredibly delicate instruments that are the product of billions of years of evolution. So congratulations! You can now answer the question of how we hear and appreciate the sheer complexity of human hearing.
Post By: Armaan G.
Photo credits: Pixabay, CSTRSK, https://pixabay.com/illustrations/sound-wave-voice-listen-856771/
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