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The mechanical force applied to the head displaces the brain. Depending on the direction and magnitude of the force, certain neurological functions can be disrupted. The damage to the brain within the skull can present as strain, tissue distortion and shearing of axons. The processes for damage control are activated immediately, while the damage continues to evolve. The damage occurs as a result of the cellular and molecular processes taking place in response to mechanical forces. First, the mechanical force disrupts the neuronal membrane, which rapidly increases the extracellular potassium concentration. This activates a positive feedback loop where more potassium ions are released, which leads to a cascade of responses that eventually lead to a period of hyperglycolysis in the brain followed by higher permeability of the Blood-Brain-Barrier (BBB) and the induction of cytotoxic edema in the brain.<ref name="Arti13">Giordano, K. R., & Lifshitz, J. (2021). Pathophysiology of Traumatic Brain Injury. In S. Honeybul & A. G. Kolias (Eds.), Traumatic Brain Injury. Springer. https://doi.org/10.1007/978-3-030-78075-3_2 </ref> The latter has a detrimental effect on all cells in the brain tissue.
Very important cell types in the brain, aside from neurons, are the neuroglia. These cell types are broadly recognized as having a supportive role. There are 6 types of neuroglia, each with their own function [[File:Types-of-neuroglia_brain-physiology-cells-QBI.png|thumb|250px|Types of glia. <ref name="Arti16">https://qbi.uq.edu.au/brain-basics/brain/brain-physiology/types-glia</ref>]]. In the central nervous system (CNS), the astrocytes are a main type of glial cells. They contribute to the maintenance of homeostasis in the CNS through reactive astrogliosis.<ref name="Arti14">Sofroniew, M. V., & Vinters, H. V. (2009). Astrocytes: biology and pathology. Acta Neuropathologica, 119(1), 7–35. https://doi.org/10.1007/s00401-009-0619-8 </ref> This process is triggered by all types of brain insults and has features that aid recovery, but simultaneously have a potential to inflict damage on the brain. For example, the astrocytes break down their glycogen to supply adjacent neurons with lactate, which the neurons use as fuel to recover. However, the astrocytes also play a critical role in water movements through the brain and in pathological conditions, this can mediate oedema. In all cases of reactive astrogliosis, GFAP is up-regulated. The degree to which the GFAP expression changes, is only dependent on the severity of the trauma to the CNS and not on the morphological appearance of the reactive astrogliosis. <ref name="Arti15">Verkhratsky, A., & Butt, A. (2013). General Pathophysiology of Neuroglia. In Glial Physiology and Pathophysiology (1st ed.). John Wiley & Sons, Ltd. https://doi.org/10.1002/9781118402061 </ref>
== References ==
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