Anatomy of the Ear

Parts of the Ear

The ear is a fascinating and complex part of the human body that allows us to hear and maintain balance. Understanding the anatomy of the ear can help you appreciate how it works and why it’s important to take care of it. Let’s break down the various parts of the ear into three main sections: the outer ear, the middle ear, and the inner ear.

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The Outer Ear

The outer ear consists of two parts: the pinna (or auricle) and the ear canal.

  • Pinna (Auricle): This is the visible part of the ear that you can see on the side of your head. It’s made of cartilage and skin. The pinna helps to collect sound waves and funnel them into the ear canal.
  • Ear Canal: This is a tube that leads from the pinna to the eardrum. The ear canal helps to protect the eardrum and also amplifies sounds.

The Middle Ear

The middle ear is an air-filled space that contains three tiny bones called ossicles, which are crucial for hearing.

  • Eardrum (Tympanic Membrane): This thin membrane separates the outer ear from the middle ear. When sound waves hit the eardrum, it vibrates.
  • Ossicles: These are three small bones known as the malleus (hammer), incus (anvil), and stapes (stirrup). They transmit vibrations from the eardrum to the inner ear.

The Inner Ear

The inner ear is a complex structure that contains the cochlea and the vestibular system.

  • Cochlea: This spiral-shaped organ is responsible for converting sound vibrations into electrical signals that the brain can interpret as sound.
  • Vestibular System: This system helps with balance and spatial orientation. It includes the semicircular canals and the otolithic organs.

How Hearing Works

Sound waves enter the ear through the ear canal and hit the eardrum, causing it to vibrate. These vibrations are passed through the ossicles in the middle ear, which amplify them and send them to the cochlea in the inner ear. The cochlea converts these vibrations into electrical signals that travel to the brain, where they are interpreted as sound.

This animated video (courtesy the National Institute on Deafness and Other Communication Disorders, National Institutes of Health) illustrates how sounds travel from the ear to the brain, where they are interpreted and understood.

How do we hear?

  1. Sound waves enter the outer ear and travel through a narrow passageway called the ear canal, which leads to the eardrum.
  2. The eardrum vibrates from the incoming sound waves and sends these vibrations to three tiny bones in the middle ear. These bones are called the malleus, incus, and stapes.
  3. The bones in the middle ear amplify, or increase, the sound vibrations and send them to the cochlea, a snail-shaped structure filled with fluid, in the inner ear. An elastic partition runs from the beginning to the end of the cochlea, splitting it into an upper and lower part. This partition is called the basilar membrane because it serves as the base, or ground floor, on which key hearing structures sit.
  4. Once the vibrations cause the fluid inside the cochlea to ripple, a traveling wave forms along the basilar membrane. Hair cells—sensory cells sitting on top of the basilar membrane—ride the wave. Hair cells near the wide end of the snail-shaped cochlea detect higher-pitched sounds, such as an infant crying. Those closer to the center detect lower-pitched sounds, such as a large dog barking.
  5. As the hair cells move up and down, microscopic hair-like projections (known as stereocilia) that perch on top of the hair cells bump against an overlying structure and bend. Bending causes pore-like channels, which are at the tips of the stereocilia, to open up. When that happens, chemicals rush into the cells, creating an electrical signal.
  6. The auditory nerve carries this electrical signal to the brain, which turns it into a sound that we recognize and understand.


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