Abstract
Rich repertoires of movements underlie the complex social interactions of mammals. The building blocks, or syllables, of these movements are produced by spinal cord circuits that are comprised of diverse neuronal types that control musculoskeletal systems comprised of multi-segmented limbs. Together, these systems provide mammals with the evolutionary advantages of power, speed, and endurance. Here, I propose that the key steps in chordate evolution that led to these traits began with the development of the notochord and a proliferative ventricular zone (with associated Notch signalling). This step led to the production of diverse neuronal types that included the development of a sympathetic nervous system that could regulate the evolving cardiovascular system. And the sympathetic nervous system in turn led to the development of homeothermic endothermy, a requirement for motor systems to produce a combination of power, speed, and endurance. Furthermore, the evolution of the continuous structure of the spinal cord led not only to a structure fit for cartesian signalling molecules, but also to one with high processing power in which circuits for effecting movement syllables formed. These syllables are harnessed by higher regions of nervous systems to produce the complex movements required for interactions with others and with the surrounding environment.
Highlights
For this issue of Neuroscience dedicated to the scientific contributions of Tom Jessell, I initially fretted about the topic to present
It is interesting that one topic that to my recollection we did not discuss was the evolution of movement
Two key advances in the early evolution of chordates were the development of the notochord and floor plate that led to neural tube induction and dorsoventral patterning, followed by the Notch signalling pathway that supported a proliferative ventricular zone (VZ)
Summary
For this issue of Neuroscience dedicated to the scientific contributions of Tom Jessell, I initially fretted about the topic to present. Key developments for the success of vertebrates were power, speed, and endurance In this brief article, which I hope is prolegomenal to further concepts along this vein, I will argue – as a physiologist rather than as an evolutionary biologist (a subject in which I have no expertise) – that these developments were possible because of the evolution of the notochord, neural tube, and ventricular zone (VZ). It was upon this backbone, so to speak, that power, speed, and endurance (and dexterity) were built These traits supported the development of the brain, such that complex social structures could evolve to make use of the spinal cord circuits that create movement syllables. In an anthropomorphic view, is an evolutionary success story that can be witnessed across the plains of Africa
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