Neurological System

The neurological system links sensation, movement, cognition, speech, autonomic function, and consciousness. The central nervous system consists of the brain and spinal cord. The peripheral nervous system carries information between the CNS and the rest of the body through cranial nerves, spinal nerves, and autonomic pathways. Neural communication depends on changing electrical charges across cell membranes. Voltage-gated sodium channels initiate depolarization, potassium channels help repolarize the membrane, and the sodium–potassium ATPase restores the ion gradients needed for repeated signalling. Myelin speeds conduction by allowing the action potential to “jump” between nodes along the axon; damage to myelin can therefore produce weakness, sensory change, or slowed coordination even when the muscle itself is intact. The blood–brain barrier limits movement of substances from the circulation into neural tissue. Inflammation, infection, trauma, and ischaemia can disrupt that barrier, allowing fluid and inflammatory mediators to enter brain tissue. The skull is a fixed container. Its contents are brain tissue, cerebrospinal fluid, and intracranial blood. When one compartment expands, the others initially shift to compensate. Once compensation is exhausted, intracranial pressure rises quickly and can...