The majority of blood flow is redirected back towards the internal organs now

The majority of blood flow is redirected back towards

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to the whole body not just to the vital organs. The majority of blood flow is redirected back towards the internal organs now that the muscles do not need most of the blood for activation. Rather the internal organs require blood flow so that they can return to homeostatic functioning. Airways in lungs constrict back to normal state transporting oxygen optimally to all cells. Palms and skin are no longer sweaty as blood vessels dilate. 2.4 The meninges and cerebrospinal fluid Considering the indispensability of the CNS to both basic and higher level functions of the body, not only is the brain protected by the cranium and the spinal cord protected by the vertebrae, further mechanisms have developed in order to offer enhanced protection. In addition to bone, the CNS is surrounded by the meninges and cerebrospinal fluid. The meninges refer to three layers of fibrous membranes that encompass the CNS and therefore function to protect the brain and spinal cord. The outer most layer of the meninges is called the dura mater, the middle layer is called the arachnoid mater and the inner most layer, the pia mater (McCaffrey, 2015). 2.4.1 The dura mater In Latin, ‘dura’ means hard and ‘mater’ means mother, so if taken literally it means ‘hard mother’ referring to both the protective and nourishing nature of this layer The dura mater is the thick, yet flexible, outermost meningeal layer located just inside the cranial bones and also lines the spinal canal. The resiliency of this layer protects the brain from displacement and functions to connect the meninges to the
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cranium. The dura mater can be further subdivided into two layers: an outer layer known as the endocranium, or periosteal layer, and a deeper inner layer referred to as the inner meningeal layer (Clark, 2005: 189). At some points in the cranium the inner and outer layers of the dura mater separate from one another forming a cavity, called the dural sinuses. The dural sinuses permit blood flow, transporting deoxygenated venous blood which has provided oxygen and nutrients to the brain, and returning it back to the cardiovascular system (Applegate, 2011: 179). 2.4.2 The arachnoid mater The arachnoid layer is attached to the inner most layer, the pia mater, by arachnoid trabeculae which have a spider web like appearance, hence the name for this meningeal layer. The space under the arachnoid mater, the subarachnoid space, is filled with cerebrospinal fluid and contains blood vessels (Applegate, 2011: 179) which ultimately join and stabilise the arachnoid mater to the pia mater. The arachnoid layer is important as it provides a space through which cerebrospinal fluid can circulate and is also necessary for the absorption of the cerebrospinal fluid back into the bloodstream. 2.4.3 The pia mater The delicate pia mater is the inner most layer of the meninges and is in direct contact with the neural tissues of the brain and spinal cord. The pia mater acts as an intermediary between the neurons of the CNS and the cerebrospinal fluid, preventing their direct contact (Clark, 2005: 189).
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