2-Minute Neuroscience: The Cochlea

In this video, I describe the passage of sound waves through the ear, which leads to the depression of the oval window, a structure found in the wall of the cochlea. I cover the three main cavities in the cochlea: the scala vestibuli, scala media, and scala tympani. Then I describe how the movement of fluid in the cochlea causes movement of the basilar membrane, which activates hair cells in the organ of Corti. The hair cells transmit the auditory information to the vestibulocochlear nerve, which carries it to the brain to be processed. For an article (on my website) that explains the cochlea, click this link: TRANSCRIPT: Welcome to 2 minute neuroscience, where I simplistically explain neuroscience topics in 2 minutes or less. In this installment I will discuss the cochlea When sound waves travel through the canal of our ear, they hit the tympanic membrane or eardrum and cause it to vibrate. This vibration prompts movement in the ossicles, a trio of tiny bones that transmit the vibration to a structure called the oval window, which sits in the wall of the cochlea. The cochlea is a tiny coiled structure in the inner ear that resembles a snail shell. The interior of the cochlea consists of three fluid-filled canals that run parallel to one another: the scala vestibuli, the scala media, and the scala tympani. The scala vestibuli and scala tympani contain a fluid called perilymph and the scala media contains a fluid called endolymph. When the oval window is depressed by the ossicles it creates waves that travel through the fluid of the cochlea, and these waves cause a structure called the basilar membrane to move as well. To visualize the function of the basilar membrane it can be helpful to imagine the cochlea uncoiled. When waves flow through the fluid in the cochlea, they create small waves within the basilar membrane itself that travel down the membrane. Different sections of the basilar membrane respond to different frequencies of sound and as the waves progress down the membrane, they reach their peak at the part of the membrane that responds to the frequency of the sound wave created by the original stimulus. In this way, the basilar membrane accurately translates the frequency of sounds picked up by the ear into representative neural activity that can be sent to the brain. The translation of the movement of the basilar membrane into electrical impulses occurs in the organ of Corti, which is the receptor organ of the ear. It sits atop the basilar membrane and contains receptor cells known as hair cells. Hair cells are so named because protruding from the top of each cell is a collection of small “hairs“ called stereocilia. When the basilar membrane vibrates, this causes movement of the hair cells and their stereocilia; movement of the stereocilia opens ion channels and causes the release of neurotransmitters to propagate the auditory signal to the vestibulocochlear nerve, which will carry the information regarding the auditory stimulus to the brain to be analyzed and perceived. REFERENCE: Nolte J. The Human Brain: An Introduction to its Functional Anatomy. 6th ed. Philadelphia, PA. Elsevier; 2009.