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A ‘Connectome’ like no other: Our Wired Nerves

By: , Posted on: October 30, 2020

The nerve ‘wiring’ of humans and animals has a compelling and often unappreciated biology. ‘Nerves’, or bundles of axons (our ‘wires’) that constitute the peripheral nervous system and their connections, with infiltration throughout the body, possess unique structure and function. Without nerves, there is no sensation and no movement. How they are targeted by disease and injury and how they regenerate is a fascinating story.

 

Our Wired Nerves: The Human Nerve Connectome relays this story in a format approachable by the public and by those new to the field. This book, published in August 2020, was compiled by Douglas Zochodne, a neuroscientist and neurologist at the University of Alberta in an effort to raise awareness and remind neuroscientists of the elegant biology of nerves, sometimes a neglected field, and to emphasize to all how common and difficult their disorders are. 

The book leads with an overall introduction into the peripheral nervous system, then examines its structural beauty: axons, their partnering Schwann cells, and their unique terminals infiltrating almost all parts of the body. Who would have thought that axons, the electrical connections between the brain, spinal cord and body, come in varying flavours and relationships with their partnering glial Schwann cells? These glial cells are unique to peripheral nerves and differ from their cousins in the central nervous system. Schwann cells not only layer an insulation sheath around axons to ramp up their conducting properties, they also exchange molecules and interact with axons in unexpected ways. How does a supposedly simple system of wires convey the touch of a mosquito, the pain from a burn, or the sensation of hair moving in the wind? The human skin includes a layered array of sensory receptors, that detect that annoying mosquito, burn, or wind and send a signal to axons and upward to the brain. We eventually become aware of danger or touch, but our sensory arrays require filtering before they reach our consciousness.

Exploring the book chapters

Chapter 1, “Elegant wiring:  Structural beauty of the peripheral nervous system”, explores how the wiring is laid out. How information, in the form of electrical action potentials, is transmitted is considered in Chapter 2, “Constantly think physiology: Structure meets function”. Among other topics, the interesting  complexity of taste and the role of bitterness on our tongue are also addressed . While examples of how all this wiring goes awry is covered in Chapter 3, “Irreversible events: How nerves are injured”. Some neuropathies arise from trauma that may interrupt their function temporarily or more permanently. Others arise from disease, and the term ‘polyneuropathy’ refers to a neuropathy that widely targets nerves. Overall, they are a very diverse group of conditions requiring a careful set of neurological tests to unravel them. “Are there nerves? How to test the peripheral nervous system” is a key chapter; there is a reason why peripheral neurologists carry around rubber hammers and tuning forks! 

Our Wired Nerves: The Human Nerve Connectome includes a chapter on ‘locked in’ syndrome (Chapter 6), which is a frightening condition involving widespread failure of nerves with paralysis and loss of sensation in the limbs, but preserved awareness. This rare condition may occur in a generalized and rapidly evolving form of neuropathy known as Guillain-Barre syndrome, or GBS. GBS, an inflammatory disorder of nerves and can strike unexpectedly, often triggered by a previous viral or bacterial infection. Neuropathies may result from direct nerve infection, such as leprosy, from inherited disorders that can appear in childhood or later in adults, or from damage by an unusual set of proteins known as amyloid. Polyneuropathy in diabetes mellitus (both type 1 and 2) presents with pain and tingling in the feet and predisposes persons to unrecognized injuries, or ulcerations of their feet. Chapter 7, “The disrupted connectome and pain”, summarizes existing ideas on how this condition develops with roles for ‘hyperexcitable axons’, remodeled neurons and altered pain circuitry throughout the neuraxis.

“Hope and Change: regrowth of nerves” (Chapter 8) describes the exciting neurobiology of peripheral axon regeneration. While current therapies are not available beyond reconnecting severed nerves, new molecular approaches are on the horizon to lessen the impact of neuropathic damage. For example, neurons and axons are normally reluctant to grow, preferring to maintain the status quo, the existing wiring. Recent work has uncovered a series of molecules and pathways that brake unwarranted growth but also brake regeneration. Manipulating these pathways is one of several opportunities to enhance the regeneration of nerves. The final chapter of  Our Wired Nerves is to celebrate a few physician and scientist heroes in this field, brought together by a group known as the  Peripheral Nerve Society, who have had the passion and interest to push the boundaries.

Ready to read the book?

Our Wired Nerves: The Human Nerve Connectome, reviews the essential anatomy and physiology of the peripheral nerve. It introduces the reader to what neuropathies are, how pain arises from damaged nerves and how nerves might be regenerated, including new and exciting ideas over how to coax their regrowth. 

Our Wired Nerves: The Human Nerve Connectome is available now on ScienceDirect. Or purchase your own copy from the Elsevier.com bookstore and save 30% + get free shipping with promo code STC30.

 

 

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