The Glasgow Coma Scale (GCS) is a standardized 15-point assessment tool that quantifies the level of consciousness by evaluating three neurological domains — eye opening (E1-4), verbal response (V1-5), and motor response (M1-6) — each reflecting the functional integrity of specific neuroanatomical structures. Consciousness requires two intact components: arousal (maintained by the ascending reticular activating system [ARAS] in the brainstem tegmentum, projecting through the thalamus to diffusely activate the cerebral cortex) and awareness (mediated by the cerebral cortex itself). Eye opening assesses arousal: spontaneous opening (E4) indicates intact ARAS-thalamo-cortical arousal circuits; progressive loss reflects increasing brainstem dysfunction. Verbal response evaluates cortical integration: oriented speech (V5) requires intact dominant hemisphere language areas (Broca and Wernicke), temporal lobe memory circuits, and prefrontal executive function; confusion (V4) suggests diffuse cortical dysfunction; incomprehensible sounds (V2) indicate severe cortical damage with only brainstem vocalization preserved. Motor response is the MOST prognostically important component: localizing to pain (M5) confirms intact corticospinal tract and sensory cortex; flexion withdrawal (M4) requires intact spinal reflex arcs with cortical modulation; abnormal flexion/decorticate posturing (M3) indicates damage ABOVE the red nucleus...