Spinal cord, white matter and gray matter

Spinal cord

Spinal cord is the part of the central nervous system.
Human nervous system is divided into three parts-
      1. Central nervous system                                      
      2. Peripheral nervous system
        3. Autonomic nervous system

      Central nervous system is further divided into brain and spinal cord.
      Spinal cord connects the periphery of the body to main central system.
      Spinal cord consists of large number of spinal tracts that carries sensory and motor impulses up and down through ascending and descending tracts.
      Spinal cord lies loosely in the vertebral canal.
      It extends from foramen magnum where it is continuous with medulla oblongata, above and up to the lower border of first lumbar vertebra
      Spinal cord is cylindrical in shape.
      Length of the spinal cord is about 45 cm in males and about 43 cm in females.

      spinal cord

        Meninges-

      Coverings Spinal cord is covered by sheaths called meninges, which are membranous in nature.

      Meninges are dura mater, arachnoid mater and pia mater.

      These coverings continue as coverings of brain.

      Meninges are responsible for protection and nourishment of the nervous tissues.
      Shape and Length Spinal cord is cylindrical in shape. 

      Enlargements Spinal cord has two spindle-shaped swellings, namely cervical and lumbar enlargements.

      These two portions of spinal cord innervate upper and lower extremities respectively.


          Conus medullaris-

          Below the lumbar enlargement, spinal cord rapidly narrows to a cone-shaped termination called conus medullaris.


          Filum terminale-

          A slender non-nervous filament called filum terminale extends from conus medullaris downward to the fundus of the dural sac at the level of second sacral vertebra.
          Segments Spinal cord is made up of 31 pairs.
          • cervical nerve roots-8
          • thoracic nerve roots-12
          • Lumbar nerve roots-5
          • Sacrum nerve roots--5
          • coccyx nerve root-1
          • Total-  31
            Appearance of the segment is by nerves arising from spinal cord, which are called spinal nerve. 

            Spinal Nerves Segments of spinal cord correspond to 31 pairs of spinal nerves in a symmetrical manner.
            Nerve Roots Each spinal nerve is formed by an anterior (ventral) root and a posterior (dorsal) root.
            Both the roots on either side leave the spinal cord and pass through the corresponding intervertebral foramina.
              The first cervical spinal nerves pass through a foramen between occipital bone and first vertebra, which is called atlas.
              Cervical and thoracic roots are shorter whereas, the lumbar and sacral roots are longer.

              Long nerves descend in dural sac to reach their respective intervertebral foramina. 
              This bundle of descending roots surrounding the filum terminale resembles the tail of horse. Hence, it is called cauda equina.


              Gray matter of spinal cord-

                Gray matter of spinal cord is the collection of nerve cell bodies, dendrites and parts of axons.

                It is placed centrally in the form of wings of the butterfly and it resembles the letter ‘H’.

                Exactly in the center of gray matter, there is a canal called the spinal canal.

                Ventral and the dorsal portions of each lateral half of gray matter are called ventral (anterior) and dorsal (posterior) gray horns respectively.

                The gray matter forms a small projection in between the anterior and posterior horns in all thoracic and first two lumbar segments. It is called the lateral gray horn.

                Part of the gray matter anterior to central canal is called the anterior gray commissure and part of gray matter posterior to the central canal is called posterior gray commissure.


                        White matter of spinal cord-

                          White matter of spinal cord surrounds the gray matter.

                          It is formed by the bundles of both myelinated and unmyelinated fibers, but predominantly the myelinated fibers.

                          Anterior median fissure and posterior median septum divide the entire mass of white matter into two lateral halves.

                          The band of white matter lying in front of anterior gray commissure is called anterior white commissure.

                              Read more-
                                              Spinal cord disease
                                            Spina bifida
                                            Chiari Malformation
                                            Cauda Equina Syndrome

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