Anatomy of the Ear


The ears are designed to gather sound waves via the outer ear, but they also enable the brain to determine the position of the head and body as well as maintaining balance.

The anatomy of the ear is split into 3 sections: the outer ear, middle ear and inner ear.

The outer ear

The outer, or external, ear is the only part that is easily visible to us, and is comprised of the pinna or auricle. It includes the helix, the curved outer rim and the antihelix, the inner curve which includes the ear canal and tympanic membrane (also known as the ear drum). There is a small fleshy part that protrudes and partly covers the ear drum, called the tragus, and on the opposite side there is the antitragus. The concha is the hollow area, normally around 2.5cm long, that lies in front of the ear canal.

Sound is caught by this intricate design of the ear, and is directed down the ear canal.

The entry into the ear canal is surrounded by cartilage for protection, but it turns to bone as it nears the eardrum. This is known as the auditory bulla and is formed by the temporal bone tympanic part.

The ear wax that is used to keep the ears moist and clean is produced in the skin in the ear canal by the ceruminous and sebaceous glands.

The middle ear

The middle part of the ear is mostly just made up of empty space full of air, and houses the three smallest bones in the human body. As a group they are called ossicles, but each has an individual name that describes the shapes that they resemble - the malleus (hammer), the incus (anvil) and stapes (stirrup).

When the sound waves hit the tympanic membrane (ear drum), it vibrates, in turn causing the ossicles to move – they amplify the sound around 15-20 times. There is a thin membrane that divides the middle and inner ear, called the oval window, which the sound is passed on through.

The inner ear

The inner ear is another hollow cavity within the temporal bones of the skull, on each side of the head, and is where the sound waves are converted to electrical signals for the brain to process.

The structure in the inner ear that does this is the cochlea which is spiral shaped and somewhat reminiscent of a snail's shell. Inside the cochlea is the organ of corti, which is filled with fluid and contains thousands of specialised sensory hair cells called cilla.

As the sound waves travel into here, tiny ripples and waves are formed in the fluid inside the cochlea, causing the cilla to move and vibrate. These vibrations are then converted into nerve impulses so the brain can understand them; as the hairs ride the waves up and down, their pores open at the tips, causing chemicals to rush through the open pores into the cells.

Balance

We also mentioned earlier than the ears help to control balance, and this is carried out in the inner ear, too.

The part that does this is the structure called the vestibular system, which is made up of the semicircular canals and the otolith organs, two small fluid-filled recesses called the saccule and utricle.

The semicircular cells contain fluid and cilla just like the cochlea, and as the sound enters the round window (fenestra cochlea), they create more nerve impulses for the brain, which is used to understand the position of the head.

The otolith organs have the same workings of fluid and cilla, but focus on helping the brain detect the position of the body relative to gravity instead.

All of these work together to enable the brain to balance the body by moving it into the correct posture, position and angle!

Ear related AnatomyStuff resources:

Ear, Nose and Throat Chart / Poster - Laminated

Budget Middle Ear Model (3 times life size, 2 part)

Budget Giant Ear Model (5 times life size, 6 part)

Life-size Auditory Ossicles Model

Life-size Human Ear Model

Further reading / sources:

Vestibular system:
https://www.neuroscientificallychallenged.com/blog/know-your-brain-vestibular-system
Balance:
https://www.asha.org/public/hearing/How-Our-Balance-System-Works/

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