White matter

WHITE MATTER

  • It forms the tract systems of the spinal cord containing myelinated nerves, and they transmit sensory impulses through ascending tracts and the motor impulses through the descending tracts between the spinal cord and the higher centres of the brain.
  • The white matter is divided into paired dorsal funiculi, ventral funiculi and two lateral funiculi
    • Ascending (Sensory) tracts of spinal cord
    • Dorsal funiculus
      • Is composed of two ascending fiber tracts
      • These terminate in the medulla oblongata
      • The fasciculus gracilis terminates on the nucleus gracilis of the medulla
      • The fasciculus cuneatus terminates on the nucleus cuneatus and nucleus cuneatus lateralis of the medulla
      • But many of the fibers of the Dorsal funiculus terminate in the gray matter of the spinal cord before the rest enter the medulla
      • These fibers support intersegmental reflex activity and a portion them terminate on the cells of the nucleus proprius , nucleus dorsalis and nucleus intermedialis, and these further give rise to another system that ascends like the spinocerebellar, spinobulbar and spinothalamic tracts
      • The fasciculus gracilis and fasciculus cuneatus are also arranged somatotropically
      • Ascending fibers from the coccygeal, sacral, lumbar and thoracic levels comprise the fasciculus gracilis
      • Fibers from the cervical and upper cervical (T1) comprise the fasciculus cuneatus
      • As these fibers represent sensory information , the ipsilateral surface of the body is represented topographically within the dorsal funiculus
      • The fibers of the Dorsal funiculus convey impulses from joint receptors, muscle spindle and golgi tendon organ, cutaneous receptors for tactile and pressure sensations and so relay sensations related to joint movement and position.
      • Fibers from joint afferents and skin afferents terminate in the spinal cord for reflex mechanisms or within the nucleus gracilis and nucleus cuneatus of medulla for relay to thalamus and then cortex.
Last modified: Monday, 26 December 2011, 8:53 AM