Chapter 12: The Central Nervous System

The central nervous system serves as the command center for coordinating body functions through integrated networks of neurons and supporting cells that process sensory information and generate coordinated motor responses. This chapter establishes the foundational anatomy and physiology of neural tissue by distinguishing the brain and spinal cord from the distributed peripheral nervous system and explaining how the autonomic nervous system splits into opposing sympathetic and parasympathetic divisions that maintain homeostatic balance. Neurons, classified structurally as multipolar, bipolar, or unipolar and functionally as sensory, motor, or interneuronal, operate alongside specialized glial cells including astrocytes, microglia, oligodendrocytes, and Schwann cells that provide metabolic support, immune defense, myelin formation, and insulation essential for proper neural function. The chapter explores how neurons generate and propagate electrical signals through changes in membrane potential governed by sodium and potassium ion gradients maintained by the sodium-potassium pump, establishing the resting potential and enabling depolarization and repolarization cycles that underlie neural signaling. Action potentials represent all-or-nothing electrical events that propagate along axons with greater efficiency in myelinated fibers through saltatory conduction, allowing rapid communication across distances. The transition from electrical to chemical signaling occurs at synapses where neurotransmitters released from presynaptic terminals bind to postsynaptic receptors, generating excitatory or inhibitory postsynaptic potentials that determine whether downstream neurons fire. Neurotransmitters including acetylcholine, dopamine, serotonin, and gamma-aminobutyric acid exert diverse physiological effects ranging from muscle contraction to mood regulation and synaptic inhibition. Together these mechanisms establish the cellular and molecular basis for sensation, integration, and motor control that allows the nervous system to maintain internal stability and coordinate responses to environmental demands.