14.3 Sectional Anatomy of the Spinal Cord

• Spinal cord contains central mass of gray matter contains cell bodies of neuroglia and cell bodies of neurons and peripheral region of white matter contains myelinated and unmyelinated axons 
• Anterior median fissure and posterior median sulcus divide spinal cord into left and right halves
• Central H-shaped mass of gray matter containing cell bodies of neuroglia and neurons
• Gray matter surrounds narrow central canal, located in horizontal bar of H
• Gray matter called horns project toward outer surface of spinal cord
• Peripheral white matter contains myelinated/unmyelinated axons organized into tracts/columns
• Organization of Gray Matter. Cell bodies of neurons within gray matter of spinal cord organized into groups called nuclei that have specific functions
• Organization of Gray Matter. Sensory nuclei receive and relay sensory info from peripheral receptors, such as touch receptors in skin
• Organization of Gray Matter. Motor nuclei send motor commands to peripheral effectors, such as skeletal muscle
• Organization of Gray Matter. A frontal section along the axis of central canal separates sensory nuclei from motor nuclei
• Organization of Gray Matter. Posterior (dorsal) horns contain somatic and visceral sensory nuclei, and anterior (ventral) horns contain somatic motor neurons
• Organization of Gray Matter. Lateral horns (intermediate horns) contain visceral motor neurons
• Organization of Gray Matter. Gray commissures contain axons decussating from one side of cord to the other
• Organization of White Matter. White matter is divided into regions or columns
• Organization of White Matter. Posterior white columns are located between posterior horns and posterior median sulcus
• Organization of White Matter. Anterior white columns located between anterior horns and anterior median fissure, interconnected by anterior white commissure
• Organization of White Matter. Lateral white columns, between anterior and posterior columns are composed of white matter
• Organization of White Matter. Each column contains tracts composed of axons sharing functional and structural characteristics
• Organization of White Matter. Tract carries sensory information or motor commands
• Organization of White Matter. Axons within tract same in diameter, myelination, conduction speed, direction
• Organization of White Matter. Small tracts carry sensory or motor signals between spinal cord. Large tract connect spinal cord with brain
• Organization of White Matter. Ascending tracts carry sensory information toward brain. Descending tracts carry motor commands into spinal cord
• A patient with polio, a viral infection of motor neurons, has lost the use of his leg muscles. In what area of his spinal cord would you expect to find the infected motor neurons?

  Since the poliovirus would be located in the somatic motor neurons, we would find it in the anterior horns of the spinal cord where the cell bodies of these neurons are located.
• What is the difference between ascending tracts and descending tracts in the white matter?  


  Ascending tracts carry sensory information toward the brain. Descending tracts carry motor commands into the spinal cord.