Anatomy of spinal cord (external features, spinal segments, spinal nerves & covering meninges)

📌 Gross Features

• Length: 45 cm approximately
• Occupies upper two-thirds of vertebral canal [MCQ]
• Begins: continuation of Medulla Oblongata below Foramen Magnum
• Ends: lower border of L1 in adults [MCQ]

🖇 Developmental Changes

• 3rd month fetal: fills entire vertebral canal
• At birth: ends at L3 [MCQ]
• Adult: ends at L1
• Growth slower than vertebral column

🚨 Key Anatomical Terms [MCQ/Written]

• Conus Medullaris: conical lowest part of spinal cord
• Filum Terminale: fibrous extension of Pia Mater from conus → coccyx
• Cauda Equina: bundle of lumbar, sacral, coccygeal nerves below L1

🟠 Spinal Segments & Enlargements

• 31 segments total (8C, 12T, 5L, 5S, 1Co)

Cervical Enlargement:

• Location: C4-T1 [MCQ]
• Forms: Brachial Plexus

Lumbar Enlargement:

• Location: L1-S4
• Forms: Lumbar & Sacral Plexuses

🟣 Internal Structure

Gray Matter Horns:

• Dorsal Horn: Sensory fibers
• Ventral Horn: Motor fibers
• Lateral Horn: Autonomic fibers (Lower thoracic, lumbar, upper sacral only) [MCQ]

Spinal Nerve Formation:

• Dorsal Root (sensory) + Ventral Root (motor) = Mixed Spinal Nerve
• After exit → divides into:
• • Dorsal Ramus: supplies back muscles/skin [MCQ] (no plexuses)
  • Ventral Ramus: forms plexuses, supplies anterolateral trunk/limbs
• Both rami are mixed

📌 Vertebral-Segmental Correlation [MCQ]

• Cervical vertebrae: Add 1
• T1-T6: Add 2
• T7-T9: Add 3
• T10: L1, L2 segments
• T11: L3, L4 segments
• T12: L5 segment

🖇 Meninges

1. Dura Mater (outermost):

• Ends at S2 [MCQ]
• Extradural space: fat + connective tissue [MCQ contents]

2. Arachnoid Mater (middle):

• Ends at S2 [MCQ]
• Subarachnoid space: CSF [MCQ contents]

3. Pia Mater (innermost):

• Contains blood vessels
• Ends at L1, continues as Filum Terminale

Lumbar Cistern: L2-S2, large CSF volume

Denticulate Ligaments: Pia extensions → fix spinal cord, prevent displacement [Written]

🚨 Protection & Fixation Factors [Written]

1. Vertebral Column
2. Meninges (Dura, Arachnoid, Pia)
3. Extradural Space (fat + connective tissue)
4. CSF (shock absorber)
5. Filum Terminale (inferior fixation)
6. Denticulate Ligaments (prevent displacement)
7. Spinal Nerve Roots
8. Dura fixation at Foramen Magnum

🟠 Clinical Application: Lumbar Puncture [MCQ/Written]

• Site: between L3-L4 vertebrae [MCQ]
• Safety Zone: Lumbar Cistern (L2-S2)
• Safety: cord ends at L1, only mobile Cauda Equina present
• Diagnostic: CSF pressure measurement, sample analysis
• Therapeutic: reduce pressure, drug injection (spinal anesthesia)