Cerebral Hemispheres 2
NEUROSCIENTIFICALLY CHALLENGED

NEUROSCIENCE MADE SIMPLER

History of neuroscience: Charles Scott Sherrington


sherrington.jpg

To many, Charles Scott Sherrington is best known for providing us with the term synapse, a word we still use to describe the junction where two neurons communicate. While Sherrington's work to understand synapses and neural communication was important, however, his studies of reflexes, proprioception, spinal nerves, muscle action, and movement were much more expansive and probably even more influential.

Regardless, his observations concerning synapses are representative of the meticulous care with which he investigated and made deductions about the nervous system and its function. His writings on the synapse came at a time when Santiago Ramon y Cajal was beginning to convince the scientific community that the brain consists of separate nerve cells (which became known as neurons in 1891) rather than a continuous "net" of uninterrupted nerves. One thing missing from this theory was an understanding of how neurons might communicate with one another.

In writing on that issue, Sherrington proposed a specialized membrane---which he termed a synapse---that separates two nerve cells that come together. Microscopes of the day couldn't actually observe the separation found at synapses (which is minutely small), so Sherrington was forced to describe the synapse as a purely functional separation---but a separation nonetheless. He based his hypothesis on observations he made in his own research like the fact that reflexes (which he studied extensively) weren't as fast as they should be if they involved simply conducting signals along continuous nerve fibers. Sherrington had originally planned to use the term syndesm to describe the functional junction between neurons, but a friend suggested synapse, from the Greek meaning "to clasp," since it "yields a better adjectival form." 

Thus the term synapse was born, but for Sherrington his observations about the synapse were really just one part of a much greater investigation into reflexes and nerve-muscle communication. He made an important contribution in this area when he helped to elucidate the mechanism underlying the famous knee-jerk reflex (which you've likely experienced when a doctor has tapped just below your kneecap to cause your leg to kick outwards).

His work on spinal reflexes also led Sherrington to another seminal hypothesis. He proposed that muscles don't just receive innervation from nerves that travel to them from the spinal cord but that they also send sensory information about muscle length, tension, and position back to the spinal cord. Sherrington believed that this information is important for things like muscle tone and posture. He hypothesized that there are receptors in the muscle that convey this type of information, and he specifically identified muscle spindles and golgi tendon organs as potential receptors that send information about stretch and tension, respectively (this would later be confirmed). To describe the information these muscle receptors send, Sherrington coined another termproprioception. He chose this term because proprius is Latin for "own" and he wanted to emphasize that the sensory information sent from these muscle receptors comes from an individual's own body, and is not initiated by an external stimulus (as is common with other receptors).

Among Sherrington's many other contributions to understanding movement and muscle function, he also helped to develop a better understanding of the mechanism underlying something called reciprocal innervation. Reciprocal innervation refers to the way in which the activation of one muscle influences the activity of other muscles. This is a common and necessary response. As we walk across the floor, for example, when the muscles involved in the extension of one leg are activated, the muscles involved in the retraction of that same leg must be inhibited. Otherwise, our muscles would constantly be competing with one another, which would result in complete rigidity and make movement (or even standing in one place) impossible. Sherrington didn't discover the phenomenon of reciprocal innervation, but he spent years studying it and in the process gave us a better understanding of how it works. His investigations of reciprocal innervation led to a number of experiments on complex reflexes involved in movements like walking, running, and even scratching. His work helped us to understand how some reflexes involve chaining together several simple reflexive actions to create a seemingly complicated behavioral display.

Sherrington's focus on spinal nerves and reflexes led him to map the motor nerves traveling from the spinal cord to the muscles and the sensory nerves traveling from the muscles to the spinal cord---a task which took him almost ten years. He also explored the functionality of these nerves, helping to create a map of the area of the body served by a single spinal nerve (areas known as dermatomes). And he mapped the ape motor cortex, expanding on previous maps that had been made with dogs and monkeys.

Thus, although Sherrington may be best known for his naming of the synapse, his other work---which was broad but focused a great deal on muscles, movement, and reflexes---was probably even more valuable to our overall understanding of the nervous system. Sherrington won the Nobel Prize for Medicine in 1932 just as he was entering into his retirement, as recognition for his wide-ranging contributions to neuroscience. He continued to write into retirement, and branched out from scientific writing to publish a collection of poems as well as a book that focused on philosophical themes like the relationship between the mind, brain, and soul. He died in 1952 at the age of ninety-five.

Finger S. Minds Behind the Brain. New York, NY: Oxford University Press; 2000

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.

  • 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

  • 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

  • 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

  • ...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

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.

  • 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

  • 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

  • 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

  • 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