VPB 121: Veterinary Physiology - II (2+1)

GRAY MATTER

Two types of cells

• Motor neurons
• Internuncial neurons

Motor neurons

• It project their axons into the PNS 
• They are of 3 types
  • Somatic or Alpha motor neurons – supplying skeletal muscles
  • Autonomic neurons – supplying visceral organs
  • Intrafusal or Gamma motor neurons – supplying special receptors called muscle spindles
    • Somatic or Alpha motor neurons show Nissel substance in their cytoplasm
    • Internuncial neuron processes remain within the confines of the CNS
    • They vary considerably in their shape, size , organization
    • Two classes according to the course of their projection of their fibers within the nervous system
    • Commissural Internuncial neurons whose fibers cross the midline
    • Non Commissural Internuncial neurons or association neurons whose fibers do not cross the mid line
    • Association neurons are called so because by their connections they correlate activities within various portions of the nervous system
    • Gray matter of the spinal cord is divided into many nuclei on anatomical basis
    • Many portions of the CNS are said to composed of cell laminae which are groups of similar cells arranged together in a particular order