Cerebral Hemispheres 2
NEUROSCIENTIFICALLY CHALLENGED

NEUROSCIENCE MADE SIMPLER

Know Your Brain: Cochlea


Where is the cochlea?

The cochlea is a coiled structure that resembles a snail shell (cochlea comes from the Greek kochlos, which means "snail"); it is found within the inner ear. It is a small--yet complex--structure (about the size of a pea) that consists of three canals that run parallel to one another: the scala vestibuli, scala media, and scala tympani.

What is the cochlea and what does it do?

When sound waves travel through the canal of our outer ear, they hit the tympanic membrane (aka 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 ossicle bone known as the stapes taps on the oval window to pass the vibration on to the cochlea, all the while using a fine-tuned movement that preserves the frequency of the original sound wave that hit the eardrum.

The cochlea is filled with fluid. Specifically, the scala vestibuli and scala tympani contain a fluid called perilymph, which is similar in composition to cerebrospinal fluid, and the scala media contains endolymph, which more resembles intracellular fluid in terms of its ionic concentrations. When the oval window is depressed by the stapes 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.

Watch this 2-Minute Neuroscience video to learn more about the cochlea.

The basilar membrane separates the scala tympani from the scala media. When waves flow through the fluid in the cochlea, they create small ripples that travel down the basilar membrane itself (to visualize these ripples imagine the basilar membrane as a rug someone is shaking out). The basilar membrane is structured such that different sections of the membrane respond preferentially to different frequencies of sound. As waves progress down the basilar membrane, they reach their peak and then rapidly diminish in amplitude 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 around 16,000 receptor cells known as hair cells. Hair cells are so named because protruding from the top of each cell is a collection of somewhere between 50 and 200 small "hairs" called stereocilia. Hair cell stereocilia have fine fibers, known as tip links, that run between their tips; tip links are also attached to ion channels. When the basilar membrane vibrates, this induces movement of the hair cells, which causes the tip links to pull open the associated ion channels for a fraction of a millisecond. This is long enough to allow ions to rush through the ion channels to cause depolarization of the hair cell. Depolarization of hair cells leads to a release of neurotransmitters and the propagation of the auditory signal. The vestibulocochlear nerve will carry the information regarding the auditory stimulus to the brain, where it will be analyzed and consciously perceived.

Reference:

Moller, A. (1994). Auditory Neurophysiology Journal of Clinical Neurophysiology, 11 (3), 284-308.

YOUR BRAIN, EXPLAINED

Sleep. Memory. Pleasure. Fear. Language. We experience these things every day, but how do our brains create them? Your Brain, Explained is a personal tour around your gray matter. Building on neuroscientist Marc Dingman’s popular YouTube series, 2-Minute Neuroscience, this is a friendly, engaging introduction to the human brain and its quirks using real-life examples and Dingman’s own, hand-drawn illustrations.

  • ...a highly readable and accessible introduction to the operation of the brain and current issues in neuroscience... a wonderful introduction to the field. - Frank Amthor, PhD, Professor of Psychology, The University of Alabama at Birmingham, author, Neuroscience for Dummies

  • Dingman weaves classic studies with modern research into easily digestible sections, to provide an excellent primer on the rapidly advancing field of neuroscience. - Moheb Costandi, author, Neuroplasticity and 50 Human Brain Ideas You Really Need to Know

  • An informative, accessible and engaging book for anyone who has even the slightest interest in how the brain works, but doesn’t know where to begin. - Dean Burnett, PhD, author, Happy Brain and Idiot Brain

  • Reading like a collection of detective stories, Your Brain, Explained combines classic cases in the history of neurology with findings stemming from the latest techniques used to probe the brain’s secrets. - Stanley Finger, PhD, Professor Emeritus of Psychological & Brain Sciences, Washington University (St. Louis), author, Origins of Neuroscience

BIZARRE

This book shows a whole other side of how brains work by examining the most unusual behavior to emerge from the human brain. In it, you'll meet a woman who is afraid to take a shower because she fears her body will slip down the drain, a man who is convinced he is a cat, a woman who compulsively snacks on cigarette ashes, and many other unusual cases. As uncommon as they are, each of these cases has something important to teach us about everyday brain function.

  • Bizarre is a collection of stories of how the brain can create zombies, cult members, extra limbs, instant musicians, and overnight accents, to name a few of the mind-scratching cases. After reading this book, you will walk away with a greater appreciation for this bizarre organ. If you are a fan of Oliver Sacks' books, you're certain to be a fan of Dingman's Bizarre. - Allison M. Wilck, PhD, Researcher and Assistant Professor of Psychology, Eastern Mennonite University

  • A unique combination of storytelling and scientific explanation that appeals to the brain novice, the trained neuroscientist, and everyone in between. Dingman explores some of the most fascinating and mysterious expressions of human behavior in a style that is case study, dramatic novel, and introductory textbook all rolled into one. - Alison Kreisler, PhD, Neuroscience Instructor, California State University, San Marcos

  • Dingman brings the history of neuroscience back to life and weaves in contemporary ideas seamlessly. Readers will come along for the ride of a really interesting read and accidentally learn some neuroscience along the way. - Erin Kirschmann, PhD, Associate Professor of Psychology & Counseling, Immaculata University

  • Through case studies of both exceptional people as well as those with disorders, Bizarre takes us on a fascinating journey in which we learn more about what is going on in our skull. - William J. Ray, PhD, Emeritus Professor of Psychology, The Pennsylvania State University, author, Abnormal Psychology