14.1 Gross Anatomy of the Spinal Cord

• Spinal cord is continuous with brain and ends at conus medullaris. Diameter of spinal cord is largest in cervical region and smallest in sacral and coccygeal regions
• Spinal cord from foramen magnum to inferior border of first lumbar vertebra
• Posterior surface of spinal cord has shallow longitudinal groove called posterior median sulcus
• Anterior median fissure is deep crease on anterior surface of cord
• Regions of spinal cord (cervical, thoracic, lumbar) contain tracts (bundles of axons) for functions
• Gray matter increases where cord concerned with sensory and motor innervation of limb
• Gray matter areas contain interneurons responsible for… 

  • Relaying arriving sensory info 
  • Coordinating activities of somatic motor neurons that control complex muscles 
• Expanded areas of spinal cord form cervical enlargement, supplies nerves to pectoral girdle and upper limbs
• And lumbosacral enlargement supplies nerves to pelvis and lower limbs
• Caudal to lumbosacral enlargement, spinal cord forms cone-shaped tip called conus medullaris
• Extending within vertebral canal form inferior tip of conus medullaris is filum terminale 

  • Also known as terminal thread
• Entire spinal cord divided into 31 segments
• Every spinal segment associated with pair of dorsal root ganglia that contain cell bodies of sensory neurons
• Sensory ganglia lie between pedicles
• On sides of cord, dorsal roots contain afferent axons of sensory neurons in dorsal root ganglion
• Anterior to dorsal root, a ventral root leaves spinal cord
• Sensory and motor fibers form single spinal nerve that exits from intervertebral foramina
• Spinal nerves classified as mixed nerves because contains both afferent (sensory) and efferent (motor) fibers
• Spinal cord grows until age four
• After age four, vertebral column grows but not spinal cord
• Vertebral growth carries dorsal root ganglia and spinal nerves away, so dorsal and ventral roots elongate
• When seen in gross dissection, filum terminale and long ventral and dorsal roots called cauda equina
• What structure contains the cell bodies of sensory neurons?

  The cell bodies of sensory neurons are found within the dorsal root ganglion.
• The filum terminale and the long dorsal and ventral roots that extend caudal to the conus medullaris form what anatomical structure?

  Cauda equina is formed from the filum terminale and the long dorsal and ventral roots.