🖇 Central Nervous System – Spinal Cord
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📌 I. Anatomy of the Spinal Cord
Cylindrical structure inside vertebral canal.
Coverings: Dura (outer) – Arachnoid (middle) – Pia (inner, adherent).
Segments: 31 (8C + 12T + 5L + 5S + 1Coccygeal).
Enlargements: Cervical → brachial plexus / Lumbar → lumbosacral plexus.
Start & End: From foramen magnum → ends at L1–L2 → conus medullaris → filum terminale.
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📌 II. Histological Structure (TS)
Gray Matter (H-shaped, central):
Contains cell bodies, dendrites, unmyelinated fibers, neuroglia, capillaries.
Nucleus = collection of nerve cell bodies inside CNS.
Horns: Dorsal (sensory), Ventral (motor), Lateral (thoracic → sympathetic).
White Matter (peripheral):
Contains myelinated fibers, neuroglia, vessels.
Tract = bundle of fibers with same origin, course, termination, function.
Columns: Dorsal – Ventral – Lateral.
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📌 III. Gray Matter Nuclei
Dorsal Horn:
Substantia Gelatinosa → pain & temperature.
Main Sensory nucleus → crude touch.
Clarke’s nucleus → conscious proprioception.
Ventral Horn: 5 motor nuclei (central, ventromedial, ventrolateral, dorsomedial, dorsolateral).
Intermediolateral nucleus: sympathetic (thoracic segments).
Rexed Laminae: 10 layers (e.g., Lamina II = substantia gelatinosa, Lamina IX = anterior horn cells).
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📌 IV. White Matter Tracts
🟠 Ascending (Sensory)
Long tracts:
Lateral spinothalamic → pain, temp.
Ventral spinothalamic → crude touch.
Gracile (lower limb) & Cuneate (upper limb) → fine touch, conscious proprioception.
Dorsal & Ventral spinocerebellar → unconscious proprioception.
Spino-tectal, Spino-olivary.
Short tracts (4): Lissauer’s, Fasciculi proprii, Sulcomarginal, Comma-shaped.
🟣 Descending (Motor)
Pyramidal (voluntary): Corticospinal + Medial & Lateral corticobulbar.
Originate from Betz cells (Area 4).
85% fibers decussate in medulla.
Extrapyramidal (6):
Rubrospinal, Olivospinal (single).
Reticulospinal, Vestibulospinal, Tectospinal (paired).
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📌 V. Lemnisci
Definition: Fiber bundles that have crossed (decussated) → ascend to brain.
Types:
Medial lemniscus = continuation of gracile & cuneate tracts.
Spinal lemniscus = continuation of lateral & ventral spinothalamic tracts.
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🚨 Important Qs & Focus (MCQ Hotspots)
Definitions: nucleus, tract, fine vs crude touch.
Identification of spinal cord levels (cervical vs thoracic vs lumbar vs sacral).
Extrapyramidal tracts: paired vs single
Rexed classification → 10 laminae.