Anatomy

Spinal Cord Anatomy

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Spinal Cord Anatomy, Spinocerebellar Tract, Corticospinal tract, Spinothalamic Tract, Fasciculus Gracilis, Fasciculus Cuneatus, Nucleus Gracilis, Nucleus Cuneatus, Dorsal Propriospinal Tract, Posterior Column, Spinocervicothalamic Tract, Internal Arcuate Tract, Medial Lemniscus

  • Components
  • Spinal Cord Levels
  1. General
    1. Total spinal nerves: 31 pairs
    2. Spinal cord ends at L2
      1. Spinal nerves L2 to S5 descend as individual "horse hairs" (cauda equina)
      2. Nerves exit at their respective Vertebral levels
  2. Cervical Spine
    1. Cervical spinal nerves: 8 (C1-C8)
    2. Cervical nerves exit ABOVE their associated Vertebrae
      1. C1 cervical nerve exits above cervical Vertebra 1 (atlas)
      2. C7 cervical nerve exits above cervical Vertebra 7
      3. C8 cervical nerve exits above thoracic Vertebra 1
        1. Exception, as it is not associated with a cervical Vertebra (only 7 Cervical Vertebrae)
        2. Marks the transition point, after which all spinal nerves exit below their associated Vertebra
  3. Thoracic Spine
    1. Thoracic spinal nerves: 12 (T1-T12)
    2. Thoracic nerves exit BELOW the associated Vertebrae
  4. Lumbar Spine
    1. Lumbar spinal nerves: 5 (L1-L5)
    2. Lumbar nerves exit BELOW the associated Vertebrae
  5. Sacrum
    1. Sacral spinal nerves: 6 (S1-S5 and coccygeal nerve)
  • Components
  • Grey matter (central, cell bodies)
  1. Posterior horn cells (somatic sensory)
    1. Sensory fibers from the upper tracts Synapse with Lower Motor Neurons (peripheral nerves)
  2. Autonomic or visceral motor nuclei (sympathetic and parasympathetic)
    1. Visceral Motor Neurons are contained in the middle grey matter (between anterior and posterior horn cells)
    2. Fibers then course to their visceral targets (e.g. heart, abdominal viscera)
  3. Anterior horn cells (somatic motor)
    1. Motor fibers from the Corticospinal tract Synapse with Lower Motor Neurons (peripheral nerves)
  • Components
  • White matter (peripheral ascending and descending paths)
  1. Posterior Columns or dorsal columns (sensory, posterior cord)
    1. Transmits CONSCIOUS proprioception, vibratory sensation and stereognosis
      1. Also partially transmits light Touch Sensation
    2. Pathway
      1. Sensory signals rise within the spinal cord from Fasciculus Gracilis and Fasciculus Cuneatus
      2. Synapse at the Nucleus Gracilis and Nucleus Cuneatus in Medulla to form Internal Arcuate Tract
      3. Internal Arcuate Tract crosses over the midline at the Medulla to form Medial Lemniscus
      4. Medial Lemniscus courses to contralateral Thalamus and cerebral cortex
    3. Fasciculus Gracilis
      1. Transmits proprioception sensory signals from the lower part of the body
      2. Synapse at Nucleus Gracilis in Medulla, forming Internal Arcuate Tract, and then Medial Lemniscus
    4. Fasciculus Cuneatus
      1. Transmits proprioception sensory signals from the upper part of the body
      2. Synapse at Nucleus Cuneatus in Medulla, forming Internal Arcuate Tract, and then Medial Lemniscus
    5. Spinocervicothalamic Tract
      1. Located lateral to the Posterior Columns (and to the posterior root entry)
      2. Transmits sensory signals similar to the typically described Posterior Columns (gracilis and cuneatus)
        1. Transmits proprioception, stereognosis, vibration (and light touch)
  2. Spinocerebellar Tract (sensory, lateral cord)
    1. Transmits UNCONSCIOUS proprioception sensation (e.g. walking)
    2. Does not cross the midline (unlike all other sensory tracts)
      1. Courses to the ipsilateral (same side) Cerebellum via the superior and inferior peduncles
  3. Corticospinal tract (motor, lateral cord)
    1. Transmits motor signals from the cerebral cortex
      1. Pure Corticospinal tract lesions manifest as difficulty with skill movements of the distal extremities
      2. Most motor deficits (e.g. CVA, posturing) involve mixed pathways
    2. Fibers cross the midline at the Brain Stem and course to the contralateral muscles
    3. Motor fibers Synapse in the anterior horn (grey matter of the spinal cord)
      1. Upper Motor Neurons (UMN) are from the cerebral cortex to the Synapse
      2. Lower Motor Neurons (LMN) are from the Synapse to the muscle
  4. Spinothalamic Tract (sensory, anterior cord)
    1. Transmits pain and Temperature sensation
      1. Also partially transmits light Touch Sensation
    2. Fibers cross the midline within 1-2 spinal levels of their peripheral Sensory Nerve origin
      1. Courses to contralateral Thalamus and cerebral cortex (or terminates in Brain Stem)
    3. Lower extremity fibers are lateral to upper extremity fibers
      1. With external compression or injury, leg sensation may be affected earlier than arms
  • Components
  • Peripheral Nerves
  1. Sensory
    1. Enters the spinal cord via the posterior root (at the posterior horn of the grey matter)
    2. Includes a sensory Ganglion along the posterior root
  2. Motor
    1. Exits the spinal cord via the anterior root (at the anterior horn of the grey matter)
  • Components
  • Blood supply
  1. Anterior Spinal Artery (1)
    1. Supplies the anterior two thirds of the spinal column
    2. Arises inferior to the Vertebrobasilar Junction from the 2 Vertebral arteries
  2. Posterior spinal arteries (2)
    1. Supplies the posterior one third of the spinal column (in combination with intercostal arteries)
    2. Arises variably from the Vertebral arteries or posterior inferior cerebellar arteries
  • Associated Conditions
  1. Amyotrophic Lateral Sclerosis (Lou Gehrig's Disease)
    1. Anterior horns of grey matter (Lower Motor Neuron Deficit)
    2. Corticospinal tracts (upprer motor Neuron deficit)
  2. Tertiary Syphilis (Tabes Dorsalis)
    1. Posterior Columns and posterior roots and ganglia (proprioception loss and pain)
  3. Pernicious Anemia
    1. Posterior Columns (proprioception loss)
    2. Corticospinal tracts (Upper Motor Neuron Deficit)
  4. Polio
    1. Anterior horn cells of grey matter (Lower Motor Neuron Deficit)
  5. Guillain-Barre Syndrome
    1. Peripheral nerve deficit (motor and sensory)
  6. Syringomyelia
    1. Idiopathic central spinal cord (or Brain Stem) degeneration
    2. Affects crossing pain-Temperature sensation fibers (Spinothalamic Tract)
      1. Variably affects other structures (e.g. grey matter anterior horn or posterior horn cells)
  7. Spinal Cord Syndrome (Trauma)
    1. Complete transection of the spinal cord (Complete Cord Syndrome)
    2. Partial spinal cord injuries
      1. Central Cord Syndrome
      2. Anterior Cord Syndrome
      3. Spinal Cord Hemisection (Brown-Sequard Syndrome, see below)
      4. Neuropraxia (Stinger, Burner)
  8. Brown-Sequard Syndrome
    1. Spinal Cord Hemisection
    2. Results in deficits below the level of the lesion
      1. Ipsilateral paralysis (Corticospinal tract)
      2. Ipsilateral proprioception and stereognosis loss (Posterior Columns)
      3. Contralateral pain and Temperature sense loss (crossed fibers of Spinothalamic Tract)
  • Differential Diagnosis
  1. Peripheral nerve involvement
    1. Single Dermatome
    2. Peripheral Neuropathy unique pattern (e.g. Diabetic Neuropathy's stocking-glove distribution)
  2. Cortical or Brain Stem involvement
    1. Regional involvement (e.g. an entire extremity sensory or motor)
  • Anatomy
  • Images
  1. C4 Level (cross-section)
    1. cordC4.png
  2. Other images
    1. neuroSpinalCordGrayBB663.gifLewis (1918) Gray's Anatomy 20th ed (in public domain at Yahoo or BartleBy)
    2. neuroSpinalCordXsThoracicGrayBB664.gifLewis (1918) Gray's Anatomy 20th ed (in public domain at Yahoo or BartleBy)
    3. NeuroSpinalCordXsMultipleGrayBB666.gifLewis (1918) Gray's Anatomy 20th ed (in public domain at Yahoo or BartleBy)
    4. neuroSpinalCordXsMultipleGrayBB671.gifLewis (1918) Gray's Anatomy 20th ed (in public domain at Yahoo or BartleBy)
    5. neuroSpinalCordXsGrayBB672.gifLewis (1918) Gray's Anatomy 20th ed (in public domain at Yahoo or BartleBy)
    6. neuroSpinalCordGrayBB673.gifLewis (1918) Gray's Anatomy 20th ed (in public domain at Yahoo or BartleBy)
    7. neuroSpinalCordXsGrayBB675.gifLewis (1918) Gray's Anatomy 20th ed (in public domain at Yahoo or BartleBy)
    8. neuroSpinalCordGrayBB767.gifLewis (1918) Gray's Anatomy 20th ed (in public domain at Yahoo or BartleBy)
    9. neuroSpinalCordXsGrayBB770.gifLewis (1918) Gray's Anatomy 20th ed (in public domain at Yahoo or BartleBy)
    10. neuroSpinalCordGrayBB796.gifLewis (1918) Gray's Anatomy 20th ed (in public domain at Yahoo or BartleBy)
    11. neuroSpinalCordGrayBB839.gifLewis (1918) Gray's Anatomy 20th ed (in public domain at Yahoo or BartleBy)
    12. entOccipitalNerveGrayBB800.gifLewis (1918) Gray's Anatomy 20th ed (in public domain at Yahoo or BartleBy)
    13. orthoSpineLsSpinalCordCaudaEquinaGrayBB661.gifLewis (1918) Gray's Anatomy 20th ed (in public domain at Yahoo or BartleBy)
    14. orthoSpineLsSpinalCordCaudaEquinaGrayBB662.gifLewis (1918) Gray's Anatomy 20th ed (in public domain at Yahoo or BartleBy)
    15. orthoSpineLsSpinalCordCaudaEquinaGrayBB1213.gifLewis (1918) Gray's Anatomy 20th ed (in public domain at Yahoo or BartleBy)
  • References
  1. Gilman (1989) Manter and Gatz Essentials of Neuroanatomy and Neurophysiology, Davis, p. 1-16, 29-37
  2. Goldberg (2014) Clinical Neuroanatomy, p. 20-3
  3. Netter (1997) Atlas Human Anatomy, ICON Learning, p. 148-51