Sound and Hearing


Human Ear Anatomy 101:

Your ears are probably not something you think about very often. If you do, it might be in terms of whether to pierce them (maybe more than once or twice!). But our ears are really neat and how they work is amazing. They bring in all the sounds of the world around us and transmit that energy to our brain. Our brain then tells us what a certain sound is: is it a friend's whisper telling a secret, is it the hum of the engine of your very first car, or is it your little brother singing off key in the next room?

The ears have several different parts, and each has a special role which is explained below. Let's start with a general cross-sectional view of the human ear:

The Ear

Click image for a large view with descriptions.


What do our ears do?

Ears generally work as a pair to let us know where sounds are coming from. They can help us hear in '3-D' with their ability to hear something that is in front or behind us, to one side or the other, or even above or below us. Our ears work all the time, 24/7, and we can never 'turn them off'. We can hear laughter and voices, music and noise. They can detect the very softest sounds, like a whisper, and very loud sounds, like the roar of a turbine engine.

1. Outer Ear (acoustic energy):

This is the part you can see and is called the 'pinna'. It is attached to the sides of your head and is angled slightly forward, so it is most sensitive to sounds coming from in front of you. The pinna collects the sound waves (acoustic energy) and funnels this energy along the ear canal to the ear drum (tympanic membrane). This acoustic energy is a physical pressure or force that will start to vibrate the ear drum.

The Ear

Click image for a large view with descriptions.


2. Middle Ear (mechanical energy):

The middle ear space starts at the ear drum and ends at the cochlea (inner ear). It really is an air space that has the three smallest bones in the body and connects the outer ear to the inner ear. When the sound waves hit the eardrum they cause a vibration which causes the middle ear bones (ossicles) to move, literally vibrating, or carrying, the sound into the inner ear.

The Ear

Click image for a large view with descriptions.


To describe this in terms of a transducer, when the acoustic energy strikes the ear drum, causing it to move or vibrate, it is converted to mechanical energy. The bones (ossicles) in the middle ear literally work in a mechanical fashion as a system of levers to increase the sound pressure from the outer ear. This mechanical energy carries vibrations to the inner ear where yet another energy transformation will take place!

Each of these ossicles has a unique name based on its shape. There is the malleus (hammer), the incus (anvil), and stapes (stirrup). All three of them would fit onto a dime with plenty of room left over.

3. Inner Ear (hydro-mechanical energy):

The inner ear is also called the cochlea. It is about the size of a pea and shaped like a snail shell. Inside it is filled with fluid which begins to move when the middle ear transmits the sound from the outer ear. When the fluid moves it stimulates the tiny hair cells and then, they create an electrical impulse. This electrical impulse stimulates the auditory nerve which carries the signal to the brain.

The Ear

Click image for a large view with descriptions.


The inner ear is filled with fluid and when the mechanical energy is transmitted through the ossicles of the middle ear they vibrate a structure called the 'oval window' (sort of like an inner ear drum). When this oval window is stimulated it sets the inner ear fluid into motion, changing the mechanical energy into hydro-mechanical energy. This fluid (hydro) motion stimulates the hair cells (which have a mechanical action). It is here that this hydro-mechanical energy is changed into electrical energy. A tiny electrical impulse is created when these hair cells are stimulated.

Normal hair cells with stereocilia intact:

Normal Hair Cells

Abnormal hair cells with stereocilia destroyed by loud noise:

Normal Hair Cells

The hair cells are the sensory cells for hearing and when stimulated generate an electrical impulse. This impulse is carried along the auditory nerve and then to the auditory pathways which travel to the hearing centres of the brain.

Our ears and how they work forms the basics of hearing. We will be posting more information here about noise-induced hearing loss in the near future.

The Ear
What is Sound?
Sound is a vibration. When one object strikes another, a vibration is created.
How and Why it Hurts
Our body usually feels pain when it is injured. But did you know that the ears don't often feel pain?
Noise F/X: Living Loud is Hazardous
You have tons of opportunities open to you in terms of education, hobbies, and leisure activities that allow you to express yourself in individual ways.
RINGING IN YOUR EARS
Have you ever listened to loud music or noise and then noticed a ringing in your ears when you were done? The 'ringing' is called tinnitus.