ReviewThe axon as a physical structure in health and acute trauma
Section snippets
The axon
In the mature nervous system, the primary purpose of the axon is to propagate and regenerate action potentials at a consistent speed, and secondarily to this, to provide support for the energetic and signalling needs of its distal processes. Accordingly, its interior is structured to maintain its shape and calibre, and permit rapid internal transport along its length, while remaining compliant across the range of everyday movements. In large part this is attributable to the physical qualities
Extracellular matrix and surface ligands
During development, axons are formed by growth cones navigating through tissue, generating mechanical traction by means of adhesions with the extracellular matrix and other cells (O’Toole et al., 2008, Haynes and Kinney, 2011, Dent et al., 2011). These interactions determine axonal morphology, and the shape of the axon reflects a balance between internal cytoskeletal tension and the external physical environment (Bauer and ffrench-Constant, 2009). Many extracellular molecules link with proteins
Mechanical properties of CNS tissue
The brain and spinal cord are extremely soft tissues, which in vivo are suspended by arachnoid trabeculae, and float in cerebrospinal fluid. Accordingly, their mechanical properties as bulk tissue in vivo have proven difficult to measure; Meaney et al. (2014) observe that recent measurements using sensitive techniques suggest that neural tissue is an order of magnitude softer than widely cited measurements made in the 1970s to 2000s. In bulk, living neural tissue has unusual nonlinear
Normal movement
The physical environment in which axons must operate differs significantly between the CNS and the PNS. In the CNS, the surrounding tissue is more static and mechanically isolated from physical movement by arachnoid trabeculae and CSF cushioning (Meaney et al., 2014). The only major movements experienced inside the blood-brain barrier are flexions and torsions of bulk tissue, such as bending of the spinal cord within the vertebral column, rotation of the head (turning the brain with respect to
Conclusion
Popular science illustrations show neurons floating in the void, touching only at synapses. The reality is almost completely the opposite − in the CNS and peripheral nerves, every micron of the surface of the soma, dendrites and axons is physically coupled to other neurons, glia, ependymal cells, extracellular matrix or basal lamina. This tight integration, and its crosstalk with the internal cytoskeleton, is fundamental to the function and physical properties of neurons. Nowhere is this more
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Memantine Mitigates Oligodendrocyte Damage after Repetitive Mild Traumatic Brain Injury
2019, NeuroscienceCitation Excerpt :Neurofilament light chain is one of the crucial cytoskeleton proteins that play a vital role in maintaining neuronal forms and functions. Numerous studies demonstrate that concussive TBI results in cytoskeleton protein damage with destabilization of neurofilaments and microtubules (Johnson et al., 2013; Fournier et al., 2015; Kirkcaldie and Collins 2016), with dramatic impact on neuronal transport and metabolisms. Neurofilament light chain expression in peripheral blood has been used as a biomarker for neurodegeneration and axonal injury (Byrne et al., 2017; Ljungqvist et al., 2017; Weston et al., 2017).
Analysis of neurofilament concentration in healthy adult horses and utility in the diagnosis of equine protozoal myeloencephalitis and equine motor neuron disease
2019, Research in Veterinary ScienceCitation Excerpt :As a consequence of neuronal or axonal damage associated with the aging process or trauma, NFs are believed to be released into the extracellular space increasing the concentration of pNF-H in the CSF and serum (Petzold, 2015; Steinacker et al., 2016b; Steinacker et al., 2016a). Several studies have used this finding to develop biomarkers for neurodegenerative diseases and traumatic conditions in humans and experimental animals (Intan-Shameha et al., 2017; Kirkcaldie and Collins, 2016; Yilmaz et al., 2017). This study showed that although there was a positive change in the relationship between age and serum pNF-H with age, the degree of change was not high.
Understanding individual variability in symptoms and recovery following mTBI: A role for TMS-EEG?
2018, Neuroscience and Biobehavioral ReviewsCitation Excerpt :These processes are further exacerbated by degeneration due to the disruption of axonal transport cellular processes (Johnson et al., 2013). As axonal function depends on a delicate and complex interplay of cytoskeletal structure and neurochemical signalling (Kirkcaldie and Collins, 2016), traumatic loading to axons influences normal function and regulation which results in reduced synaptic activity, impaired connectivity and overall decreased efficacy of neuron function (Hill et al., 2016). The term DAI has been referred to as a misnomer (Meythaler et al., 2001), because although variable across individuals (Hellyer et al., 2013), discrete, rather than diffuse, areas of the brain experience damage.
The third wave: Intermediate filaments in the maturing nervous system
2017, Molecular and Cellular NeuroscienceCitation Excerpt :When present, NIFs are the most abundant proteins in mature axons (Perrot and Eyer, 2013) and fill the cytoplasm with a semi-rigid network under active tension against the compressive load-bearing MT network (Janmey et al., 2003). They also integrate the membrane cytoskeleton and transmembrane adhesion molecules with the interior of the axon (see Kirkcaldie and Collins, 2016, for review). As their name suggests, intermediate filament core domains are larger than actin microfilaments and smaller than MTs (Weiss and Mayr, 1971), and comprise 12-fold groupings of twinned coiled-coil N-terminal rod domains forming a linear core, from which C-terminal tails of various lengths project like bristles from a bottlebrush (Willard and Simon, 1981; Chang et al., 2009; Herrmann and Strelkov, 2011; Kornreich et al., 2015).
Peripherin: A proposed biomarker of traumatic axonal injury triggered by mechanical force
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