Hist. structure of Spinal cord I

🖇 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.