What Is the Cochlea? - Definition, Function & Location

What Is the Cochlea? - Definition, Function & Location
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  • 0:02 Sounds
  • 0:31 How We Hear
  • 1:18 The Cochlea's Role
  • 2:28 Volume and Pitch
  • 3:47 Lesson Summary
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Lesson Transcript
Instructor: Rozina Jaser
Our ear is divided into three main parts, each containing different structures responsible for different roles. This lesson focuses on our cochlea, which is found in our inner ear and is structured so that it is able to carry out its part in allowing us to hear.

Sounds

Have you ever held a seashell up to your ear and listened for the ocean wondering how the noise got trapped inside the shell? Actually, you're hearing the disturbances from air inside the shell and surrounding noise. The sounds from your environment enter the shell and bounce around the shell's interior walls mixing their frequencies and changing what you hear, thus creating an illusion of hearing ocean waves. Since that mystery has been unveiled, let's tackle another: how do we hear, anyway?

How We Hear

The human ear is divided into three parts: the outer ear, middle ear, and inner ear. The outer ear is made of cartilage and aids in collecting information through sounds around us (that's the part of our ear we can see). The eardrum, also known as the tympanic membrane, is located in the middle ear, just after the ear canal, and vibrates when sound waves reach it. When there is a disturbance in the air, sound waves travel away from the disturbance like ripples in a pond. The eardrum vibrates with the same frequency as the sound waves and transfers those vibrations through three middle ear bones that amplify the vibrations to the inner ear. The inner ear is made up of the cochlea (which contains sound detectors) and semicircular canals (which control balance).

The Cochlea's Role

The cochlea is named after the Latin word for snail shell because of its coiled snail-like shape. The walls are made of bone with a thin lining of tissue encompassing three chambers. The two large chambers include the upper vestibular canal and lower tympanic canal, which both contain fluid called perilymph. The two canals are separated by a smaller chamber called the cochlear duct, which is lined with the basilar membrane and filled with fluid called endolymph. In biology, the prefix peri- means around, and the prefix endo- means within. At the floor of the cochlear duct is the organ of Corti, which is lined with hair cells that act as receptors. Just above the organ of Corti is the tectorial membrane.

When the pressure of vibrations reaches the cochlea from the middle ear, the movement of the fluid inside the cochlea stimulates the hair receptors, which brush against the tectorial membrane. The ear then converts the energy of pressure waves into nerve impulses. Sensory neurons send nerve impulses to the cerebrum, a part of your brain, through the auditory nerves. Your brain turns those signals into sound. All this happens within fractions of a second!

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