Spinal Cord Anatomy

Topic updated on 04/09/15 1:39pm
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 q
      • 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


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Qbank (5 Questions)

(OBQ12.215) Figure A labels the neuroforamen of four vertebral motion segments. Groups A-E lists combinations of the nerve roots which exit the corresponding neuroforamen. Assuming normal vertebral anatomy with 7 cervical vertebrae, 12 thoracic vertebrae, and 5 lumbar vertebra, which group is anatomically correct? Topic Review Topic
FIGURES: A          

1. Group A
2. Group B
3. Group C
4. Group D
5. Group E

(OBQ05.196) Which artery labeled in Figure A provides the predominant blood supply to the spinal cord? Topic Review Topic
FIGURES: A          

1. A
2. B
3. C
4. D
5. None of the above



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