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Updated: May 1 2024

Spinal Cord Anatomy

Images mater.jpg tracts.jpg tracts.jpg of adamkiewicz.jpg
  • Nervous System Overview
    • Nervous system
      • central nervous system
        • includes the
          • brain
          • spinal cord
            • spinal cord ends at L3 at birth, and L1 at maturity
      • peripheral nervous system
        • contains the
          • cranial nerves
          • peripheral nerves
      • autonomic nervous system
        • sympathetic system
          • a total of 22 ganglia (3 cervical, 11 thoracic, 4 lumbar, 4 sacral)
            • cervical ganglia
              • the three cervical include the stellate, middle, and superior
                • the middle ganglion is most at risk at the level of C6 where it lies close to the medial border of the longus colli muscles
                • injury to the middle ganglion/sympathetic chain will lead to Horner's syndrome
        • parasympathetic nervous system
          • hypogastric plexus
            • formed by S2, S3, S4 parasympathetic fibers and lumbar sympathetic fibers (splanchnic nerves)
  • Spinal Cord Overview
    • Spinal cord extends from brainstem to inferior border of L1
      • conus medullaris
        • is termination of spinal cord
      • filum terminale
        • is residual fragment of spinal cord that extends from conus medullaris to sacrum.
      • thecal sac
        • the dural surrounded sac that extends from the spinal cord and contains CSF, nerve roots and the cauda equina
      • cauda equina
        • nerve roots and filum terminale surrounded by dura that extend from the spinal cord
  • Embryology of the spinal cord
    • Neural Tube
      • becomes spinal cord
      • formed from the primitive Streak, which turns into the primitive (midsagittal) groove > which turns into the Neural Tube
      • failure of the neural tube to close leads to
        • anencephaly when it fails to close cranially
        • spinal bifida occulta, meningocele, myelomeningocele when it fails to close distally
    • Neural crest
      • forms dorsal to neural tube
      • becomes the
        • peripheral nervous system
        • pia mater
        • spinal ganglia
        • sympathetic trunk
    • Notocord
      • forms ventral to neural tube
      • becomes
        • vertebral bodies
        • intervertebral discs
          • nucleus pulposus from cells of notocord
          • annulus from sclerotomal cells associated with resegmentation
  • Layers of the spinal cord
    • Layers of the spinal cord include the
      • dura mater (outside)
      • arachnoid
      • pia mater (inside)
  • Spinal Cord Functional Tracts
    • Ascending Tracts (Sensory)
      • dorsal columns (posterior funiculi)
        • deep touch, proprioception, vibratory
      • lateral spinothalamic tract
        • pain and temperature
        • site of chordotomy to alleviate intractable pain
      • ventral spinothalamic tract
        • light touch
    • Descending Tracts (Motor)
      • lateral corticospinal tract
        • main voluntary motor
        • upper extremity motor pathways are more medial(central) which explains why a central cord injury affects the upper extremities more than the lower extremities
      • ventral corticospinal tract
        • voluntary motor
  • Blood Supply
    • Spinal cord blood supply provided by
      • anterior spinal artery
        • primary blood supply of anterior 2/3 of spinal cord, including both the lateral corticospinal tract and ventral corticospinal tract
      • posterior spinal artery (right and left)
        • primary blood supply to the dorsal sensory columns
      • Artery of Adamkiewicz
        • the largest anterior segmental artery
        • typically arises from left posterior intercostal artery, which branches from the aorta, and supplies the lower two thirds of the spinal cord via the anterior spinal artery
        • significant variation exists
          • in 75% it originates on the left side between the T8 and L1 vertebral segments
  • Cerebral Spinal Fluid
    • Function
      • a colorless fluid that occupies the subarachnoid space surrounding the brain, spinal cord, and ventricular system
        • the subarachnoid space is between the arachnoid mater and pia mater
      • provides mechanical and immunological protection for the brain, spinal cord, and thecal sac
    • Production
      • location
        • most human cerebrospinal fluid (CSF) is produced by the choroid plexus in the third, fourth, and lateral ventricles of the brain.
        • CSF is an ultrafiltrate of blood plasma through the permeable capillaries of the choroid plexus
      • volume
        • total CSF volume between brain, spinal cord, and thecal sac is ~150 mL
        • CSF formation occurs at rate of ~500mL per day
          • thus the total amount of CSF is turned over 3-4 times per day
  • Nerve Root Anatomy
    • Cervical spine
      • nerve roots exit above corresponding pedicle
        • C5 nerve root exits above the C5 pedicle
      • nerve root travel horizontally to exit
      • there is an extra C8 nerve root
        • that does not have a corresponding vertebral body
    • Thoracic spine
      • nerve root travel below corresponding pedicle
        • T1 exits below T1 pedicle
        • T12 exits below T12 pedicle
    • Lumbar spine
      • nerve roots descend vertically before exiting
      • nerve root travel below corresponding pedicle
        • L1 exits below L1 pedicle
        • L5 exits below L5 pedicle
      • intrathecal anatomy
        • exiting (cranial) nerve roots are located more ventrally
        • motor fibers are located more ventrally than sensory fibers
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