Central and Peripheral Nervous Systems

The central nervous systemCentral nervous system (CNS) is composed of the brainBrain and spinal cordSpinal cord. The peripheral nervous systemPeripheral nervous system (PNS) consists of the rest of the neuronal pathways outside the brain and spinal cord. Functionally, the brain is organized in two main sections: the cerebral cortex and the subcortical areas; the latter includes the basal ganglia, hippocampus, internal capsule, brainstem, and cerebellum. The spinal cord extends from the foramen magnum to the L1–L2 level in adults. It consists of neuronal tracts that carry signals between the brain and peripheral nervous system. Cerebral blood flow (CBF) fluctuates minimally with cerebral perfusion pressure (CPP) due to corresponding changes in cerebral vascular resistanceResistance (CVR) attributed to cerebral autoregulation. CPP and CVR are influenced by pH, PaCO2, PaO2, and cerebral metabolic rate for O2 (CMRO2). CPP below the lower limit of cerebral autoregulation can lead to cerebral ischemia. AnestheticMedications medications can affect CBF and CMRO2 although no anesthetic drugs have definitively been shown to be neuroprotective in humans. During neurosurgical procedures, evoked potentials are the most commonly used neurophysiologicalNeurophysiology monitorsMonitors to detect ischemia or tissue injury in the central nervous system.