The human nervous system is the anatomical substrate that translates environmental physical energy into subjective psychological experience and coordinates complex behavioral adaptation. Composed of approximately 86 billion neurons and supported by intricate networks of glia, the system operates across macroscopic structural hierarchies spanning the central and peripheral divisions.
For CUET PG Psychology (HUQP20), Unit 4 questions on macro-neuroanatomy consistently assess:
- Taxonomy of the Nervous System: Central Nervous System (CNS: Brain and Spinal Cord) versus Peripheral Nervous System (PNS: Somatic and Autonomic).
- Peripheral Divisions: The 12 pairs of cranial nerves, 31 pairs of spinal nerves, and the autonomic antagonism between the Sympathetic (thoracolumbar) and Parasympathetic (craniosacral) divisions.
- Spinal Cord Architecture: White matter tracts, the Bell-Magendie Law (dorsal sensory, ventral motor), and the monosynaptic versus polysynaptic reflex arc.
- Brainstem, Subcortical & Limbic Systems: Medulla, Pons, Cerebellum, Midbrain colliculi, Substantia Nigra, Thalamus, Hypothalamus, Amygdala, and Hippocampus.
- Cerebral Lobes & Cortical Specialization: Frontal, Parietal, Occipital, and Temporal functions; the sensory and motor homunculi; and classic neuropsychological syndromes (Phineas Gage, Patient H.M.).
- Split-Brain Dynamics & Aphasias: Roger Sperry and Michael Gazzaniga's commissurotomy research, and differential diagnosis of Broca's, Wernicke's, and Conduction aphasias.
1. Structural Architecture of the Nervous System
Rendering diagram...
2. The Peripheral Nervous System (PNS): Somatic & Autonomic
The PNS connects the CNS to sensory receptors, muscles, and viscera. It is functionally segregated into the Somatic Nervous System (SNS) (voluntary interaction with external environment) and the Autonomic Nervous System (ANS) (involuntary regulation of internal physiological homeostasis).
A. Somatic Nervous System: Cranial & Spinal Nerves
- Afferent (Sensory) Pathways: Convey somatic sensory data inward to the CNS.
- Efferent (Motor) Pathways: Transmit voluntary motor commands outward to skeletal muscle fibers.
The 12 Cranial Nerves: Functional Taxonomy
| Nerve | Name | Modality | Primary Function & CUET High-Yield Trap |
|---|---|---|---|
| CN I | Olfactory | Sensory | Smell; bypasses thalamus directly! Projects to olfactory bulb & piriform cortex. |
| CN II | Optic | Sensory | Vision; conveys signals from retinal ganglion cells to LGN and primary visual cortex. |
| CN III | Oculomotor | Motor | Eye movements (extraocular muscles), pupillary constriction, and lens accommodation. |
| CN IV | Trochlear | Motor | Eye movement via superior oblique muscle (inward and downward gaze). |
| CN V | Trigeminal | Both (Mixed) | Primary facial tactile sensation; motor innervation of mastication (chewing). |
| CN VI | Abducens | Motor | Lateral outward eye movement via lateral rectus muscle. |
| CN VII | Facial | Both (Mixed) | Muscles of facial expression; taste sensation from anterior 2/3 of tongue; lacrimation. |
| CN VIII | Vestibulocochlear | Sensory | Cochlear division for auditory hearing; vestibular division for balance and equilibrium. |
| CN IX | Glossopharyngeal | Both (Mixed) | Taste from posterior 1/3 of tongue; swallowing and parotid gland salivation. |
| CN X | Vagus | Both (Mixed) | Carries ~75% of parasympathetic visceral tone; regulates heart, bronchi, and GI motility. |
| CN XI | Accessory | Motor | Neck and shoulder movements (sternocleidomastoid and trapezius muscles). |
| CN XII | Hypoglossal | Motor | Tongue articulation, movement, and swallowing. |
| Exam Mnemonic: Some Say Marry Money, But My Brother Says Big Brains Matter More (S = Sensory, M = Motor, B = Both/Mixed). |
The 31 Spinal Nerves: Segmental Distribution
Emerge from spinal cord segments: Cervical (8 pairs, C1–C8), Thoracic (12 pairs, T1–T12), Lumbar (5 pairs, L1–L5), Sacral (5 pairs, S1–S5), and Coccygeal (1 pair, Co1).
B. The Autonomic Nervous System: Sympathetic vs. Parasympathetic
| Feature | Sympathetic Division | Parasympathetic Division |
|---|---|---|
| Functional Role | "Fight-or-Flight" / Catabolic; mobilizes energy during acute emergency and physical exertion. | "Rest-and-Digest" / Anabolic; conserves metabolic energy and promotes digestion, nutrient absorption, and rest. |
| Anatomical Outflow | Thoracolumbar Outflow (Spinal cord segments T1–L2). | Craniosacral Outflow (Cranial nerves III, VII, IX, X; Sacral spinal segments S2–S4). |
| Ganglionic Layout | Short preganglionic fibers Paravertebral chain ganglia running parallel to the spinal column; long postganglionic fibers to target viscera. | Very long preganglionic fibers Terminal / intramural ganglia embedded directly within or adjacent to target organs; short postganglionic fibers. |
| Neurotransmitters | Preganglionic: ACh; Postganglionic: NE (Exception: ACh to sweat glands). | Preganglionic: ACh; Postganglionic: ACh (acting on muscarinic receptors). |
| Adrenal Medulla Link | Direct preganglionic discharge releases 80% Epinephrine / 20% NE into blood ("Mass Action"). | No innervation (zero parasympathetic link to the adrenal medulla). |
| Pupil of the Eye | Dilates (Mydriasis) to maximize visual field. | Constricts (Miosis) to protect retina and sharpen focal acuity. |
| Heart & Bronchioles | Tachycardia (accelerates heart rate and contractility); Bronchodilation (opens airways). | Bradycardia (decelerates heart rate); Bronchoconstriction (narrows bronchial tree). |
| Gastrointestinal Gut | Inhibits peristalsis and digestive secretions; constricts visceral blood vessels and sphincters. | Stimulates peristalsis, gastric secretions, and enzyme release; relaxes sphincters. |
| Bladder & Glycogen | Relaxes detrusor muscle; liver converts stored glycogen to free blood glucose. | Contracts detrusor muscle (promotes urination); liver synthesizes and stores glycogen. |
[!NOTE] Enteric Nervous System ("Second Brain"): Over 100–500 million neurons lining the gastrointestinal tract (myenteric and submucosal plexuses). Can operate autonomously without CNS input, synthesizing >90% of bodily serotonin.