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Vertebral Column Anatomy & Segmental Breakdown
Spinal Column Composition
| Region | Segment Count | Key Features |
|---|---|---|
| Cervical | 7 Vertebrae | C1 (Atlas), C2 (Axis); Transverse foramina |
| Thoracic | 12 Vertebrae | Costal facets for rib articulation |
| Lumbar | 5 Vertebrae | Large vertebral bodies, weight-bearing |
| Sacral | 5 Fused | Forms posterior pelvic girdle |
| Coccygeal | 4 Fused | Terminal vertebral segment |
| Total | 33 Vertebrae | Spinal cord terminates at L1–L2 |
Critical Anatomical Levels
| Level | Anatomical Landmark / Structure |
|---|---|
| C1 | Atlas (lacks vertebral body) |
| C2 | Axis (Odontoid process / Dens) |
| T8 | Inferior Vena Cava aperture |
| T10 | Esophageal hiatus |
| T12 | Aortic hiatus |
| L1–L2 | Conus Medullaris (Spinal cord termination) |
| S3 | Rectum commencement |
Cranial & Major Peripheral Nerve Reference
Cranial Nerves (CN I – CN XII)
| Nerve | Name | Primary Function / Clinical Fact |
|---|---|---|
| CN I | Olfactory | Sensory: Smell |
| CN II | Optic | Sensory: Vision |
| CN III | Oculomotor | Motor: Superior, inferior, medial recti, inferior oblique |
| CN IV | Trochlear | Motor: Superior oblique muscle (Smallest CN, emerges dorsally) |
| CN V | Trigeminal | Sensory: Facial sensation | Motor: Muscles of mastication (Largest CN) |
| CN VI | Abducens | Motor: Lateral rectus muscle |
| CN VII | Facial | Motor: Muscles of facial expression | Sensory: Anterior 2/3 taste |
| CN VIII | Vestibulocochlear | Sensory: Hearing and equilibrium |
| CN IX | Glossopharyngeal | Sensory: Posterior 1/3 taste and pharyngeal sensation |
| CN X | Vagus | Parasympathetic supply to viscera (Longest CN, extends to abdomen) |
| CN XI | Accessory | Motor: Sternocleidomastoid and Trapezius muscles |
| CN XII | Hypoglossal | Motor: Intrinsic and extrinsic tongue muscles |
Key Peripheral Nerves
| Nerve | Origin Plexus | Key Clinical Fact |
|---|---|---|
| Sciatic Nerve | Sacral Plexus (L4–S3) | Largest peripheral nerve in the body |
| Phrenic Nerve | Cervical Plexus (C3–C5) | Innervates diaphragm motor function |
| Femoral Nerve | Lumbar Plexus (L2–L4) | Innervates anterior thigh compartment (Quadriceps) |
| Obturator Nerve | Lumbar Plexus (L2–L4) | Innervates medial thigh adductor muscles |
