Academic Half Day Dec 2008 Haythum O. Tayeb Chapter 9: The
Spinal Cord
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Outline Review of: Highlights on embryology of the spinal cord
Structure of the spinal cord (anatomy) Regional charecteristics
Blood supply Functional consideration of the pathways The spinal
nerves (input and output) Grey matter columns White matter columns
Spinal Reflexes
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Embryology of the Spinal Cord
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The neural plate and caudal eminence Day 18: Neural plate
formation of neuro-ectoderm Caudal portion cervical, thoracic and
lumbar cord. Day 20 (to 42): Appearance of caudal eminence Sacral
and coccygeal levels
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Neural tube formation Day 21: the edges of the neural plate
(neural folds) enlarge posteromedially to meet at midline.
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Neural tube formation Neural fusion, starting at the adult
cervical spinal cord. Anterior neuropore closure: day 24. Posterior
neuropore closure: day 26. Neural crests detach.
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Cells of the neural tube Ventricular zone ependyma of central
canal Subventricular zone macroglia Intermediate zone basal and
alar plates (grey horns) Marginal zone axonal tracts (white
matter)
Last points Somites: Vertebrae (sclerotomes) Dermatomes (skin
and dermis) Myotomes (muscles) Relation of the spinal cord to the
vertebral column By end of 1 st trimester: both formed and have
equal length Both grow caudally but vertebral column faster Spinal
cord seems drawn rostrally. Intervertebral foramina move caudally.
Hence the cauda equina, the lumbar cistern
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Structure of the Spinal Cord
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Regional Charecteristics
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Blood Supply of the Spinal Cord
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Functional consideration of pathways
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ModalityReceptorsFiber types Exteroceptive (GSA) Pain and
temperature Bare nerve endings A (thin myelinated) C (non
myelinated) Superficial touch Meissners Corpuscles Merkels
receptors A (Medium, myelinated) Proprioceptive (GSA) Proprio-
ception Muscle Spindle Golgi Tendon Organ A (large melinated) A
(medium myelinated) Deep touch, Pressure, Vibration Pacinian
corpuscles Ruffini ending AA Interoceptive (GVA) Viscero- sensory
Visceral receptors for nociceptive stimuli C
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Grey Matter Laminae
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The white matter Tracts Ascending Descending Propriospinal
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White matter - Ascending tracts Posterior column tracts The
anterolateral system Spino- cerebellar tracts Posterior: from
Clarks (dorsal) nucleus (lamina 6,7) Anterior: from spinal border
cells (lamina 5-8)
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Posterior column tracts (gracile and cuneate fasciculi) T6
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The anterolateral system Spinothalamic Spinomesencephalic
(spinotectal, spinoperiaqueductal) Central pain modulation
Spinoreticular fibers Arousal with pain Spinohypothalamic Autonomic
and limbic responses to pain
Rubrospinal tract Present in cervical levels Stimulates flexor
tone and inhibits extensor tone Possible role in decorticate flexor
posturing Uncertain role in humans
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Reticulospinal and tectospinal tracts Reticulospinal: uncrossed
Pontine (anterior faniculus) Medullary (lateral faniculus) Extensor
tracts Tectospinal: direction of head and eye movements
In conclusion The spinal cord develops from the caudal portion
of the neural plate and the caudal eminence. The structure of the
spinal cord differs according to the level due to the varying
degrees of grey and white matter The spinal cord constitutes the
major conduit and a relay station from and to the brain, conveying
afferent and efferent somatic and visceral information. The spinal
cord also functions in spinal reflexes Knowledge of the various
pathways of the spinal cord is both fun and important in
localization in clinical neurology.
