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

STRUCTURE OF SPINAL CORD

• Cylindrical
• Extends from medulla oblongata at level of atlas for varying distances down the spinal cord

• Divided into many parts : Sensory fibers enter the spinal cord by dorsal roots of spinal nerves along the dorsolateral sulcus and motor fibers leave the spinal cord by way of the ventral roots of spinal nerves along the ventrolateral sulcus
• This arrangement divides the spinal cord into 4 compartments
• Cellular components are distributed primarily within the center of the cord where they form an H shaped column of  cells called Gray matter.
  • The grey matter has two types of multipolar neurons called the root cells‚ and the tract cells.
  • The motor neurons are the principle component of the root cells, whereas the interneurons or the fusiform neurons  form the tract cells.
• Nerve fibers are found predominantly outside of the gray matter where they form the white matter of the cord.
• The white matter is divided into components : paired dorsal funiculi ( funiculus = a bundle of nerve fibers ) , two lateral funiculi and paired ventral funiculi
• The paired dorsal fasciculi are separated by a dorsal median septum and the ventral fasciculi are separated by a ventral median fissure
• Size and shape of the spinal cord vary at different lengths
• Two distinct spinal cord enlargements are seen in domestic animals : a cervical enlargement which serve the pectoral limbs and a lumbar enlargement which serve the pelvic limbs
• Spinal cord and the vertebral column grow at the same rate during fetal life but the vertebral column grows faster in the post natal life
• This causes the spinal cord to be pulled forwards in the vertebral column.
• Spinal cord extends for different lengths along the vertebral column in different species
• Stretching out of spinal nerves arising from the caudal portion of the spinal cord forms the cauda equina
• Spinal cord is organized into segments each of which is associated with a single spinal nerve
• There are as many spinal cord segments as there are spinal nerves, But the spinal nerves and spinal cord segments do not actually correspond in adults due to differential growth. The relationship however is necessary in determining the locations of pathological processes in the spinal cord.