Clinical meaning
The nervous system is divided into the central nervous system (CNS), consisting of the brain and spinal cord, and the peripheral nervous system (PNS), consisting of 12 pairs of cranial nerves and 31 pairs of spinal nerves. The brain is organized into the cerebrum (responsible for higher cognitive functions, voluntary movement, and sensory interpretation), the cerebellum (responsible for coordination, balance, and fine motor control), and the brainstem (which controls vital functions including heart rate, blood pressure, respiratory drive, and consciousness through the reticular activating system). The Glasgow Coma Scale (GCS) is the most widely used standardized tool for assessing level of consciousness, measuring three components: eye opening (1-4 points), verbal response (1-5 points), and motor response (1-6 points), with scores ranging from 3 (deep coma) to 15 (fully alert and oriented). A GCS score of 8 or below generally indicates severe neurological impairment and the inability to protect the airway. Level of consciousness is the most sensitive indicator of neurological change and the earliest sign of deterioration. The twelve cranial nerves control specific functions that can be assessed at the bedside: olfactory (I, smell), optic (II, vision and pupillary afferent), oculomotor (III, pupil constriction and eye movement), trochlear (IV, downward eye movement), trigeminal (V, facial sensation and mastication), abducens (VI, lateral eye movement), facial (VII, facial expression and taste), vestibulocochlear (VIII, hearing and balance), glossopharyngeal (IX, swallowing and gag reflex), vagus (X, swallowing, phonation, and parasympathetic functions), accessory (XI, shoulder shrug and head turning), and hypoglossal (XII, tongue movement). Pupil assessment is critical in neurological monitoring: pupils should be equal, round, reactive to light and accommodation (PERRLA). A unilaterally fixed and dilated pupil (blown pupil) indicates compression of cranial nerve III, often from uncal herniation due to increased intracranial pressure (ICP) -- this is a neurosurgical emergency. Motor assessment evaluates strength, tone, and symmetry using a 0-5 scale (0 = no movement, 5 = full strength against resistance). Sensory assessment evaluates the ability to perceive light touch, pain (sharp/dull), temperature, vibration, and proprioception in all dermatomes. The practical nurse performs focused neurological assessments, monitors trends over time, and reports any changes promptly because neurological deterioration can progress rapidly and early intervention significantly improves outcomes. Key assessment parameters that must be trended include level of consciousness, pupil size and reactivity, motor strength, vital signs (Cushing triad of hypertension, bradycardia, and irregular respirations indicates critically elevated ICP), and cognitive orientation (person, place, time, situation).