Chapter Two - Neuromechanics: From Neurons to Brain
Section snippets
Motivation
Embedded in the skull, surrounded by the cerebrospinal fluid, and enveloped by the meninges, our brain is remarkably well protected and mechanically isolated from its environment (Nolte, 2009). It is no surprise that many scientists believe that its mechanical behavior is entirely irrelevant to its structure and function. Over the past two decades, however, we have come to realize that virtually all of the 210 different cell types in our body respond to mechanical factors, and that
Neuroelasticity
Under small deformations, our brain is essentially elastic and its deformations are almost entirely reversible. In this section, we focus on the neuroelasticity of the brain. Specifically, we restrict our attention to phenomena that take place on relatively slow time scales, where viscous effects play a less significant role. We highlight the elasticity of single neurons in Section 2.1, the elasticity of gray and white matter tissue in Section 2.2, and the elasticity of the brain in Section 2.3
Neurodevelopment
Under large deformations, over long time scales, our brain becomes inelastic and capable of adapting to environmental cues. In this section, we focus on the inelasticity associated with neurodevelopment. We restrict our attention to phenomena on relatively slow time scales, at which the brain is able to sense, respond to, and adapt to changes in its environment. We collectively refer to these phenomena as growth. While many environmental conditions may impact the brain during neurodevelopment,
Neurodamage
Under large deformations, over short time scales, our brain becomes inelastic and vulnerable to damage. In this section, we focus on the inelasticity associated with neurodamage. We consider phenomena on relatively fast time scales, on which the brain is unable to respond to environmental changes. While rate effects may play a more significant role during damage than during elasticity and development, for the sake of clarity, here we focus primarily on rate-independent effects, but include
Open Questions and Challenges
While many scientists believe that understanding the human brain is primarily a question of biochemical and electrical events, increasing evidence suggests that mechanical regulators play an equally important role in neuronal development, degeneration, regeneration, and aging (Franze et al., 2013). In this review, we have highlighted selected pathologies which undoubtably show a mechanical trace, including the prominent examples of axon elongation (Suter & Miller, 2011), cortical folding (Xu et
Acknowledgments
This study was supported by the Wolfson/Royal Society Merit Award and the EC Reintegration Grant under Framework VII to A.G., the German National Science Foundation grant STE 544/50-1 to S.B.; and the National Science Foundation INSPIRE grant 1233054 and the National Institutes of Health Grant U54GM072970 to E.K.
Glossary
- Axon
- Long, slender projection from the cell body of a nerve cell, or neuron, that transmits electrical signals from the cell body to other neurons.
- Cerebral Cortex
- Outer 2–4 mm-thick gray matter layer around the brain that consists primarily of cell bodies and plays an important role in attention, awareness, mconsciousness, language, memory, and thought.
- Cerebrospinal Fluid
- Clear and colorless body fluid that acts as a cushion for the cerebral cortex and provides a basic mechanical protection for
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