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

PYRAMIDAL AND EXTRA PYRAMIDAL SYSTEM

Descending (Motor) tracts of spinal cord

It consist of pyramidal and extra pyramidal system

• Pyramidal system
  • This system controls the voluntary and fine motor movements in association with pyramidal motor cortex.
  • This tract is well developed in primates and carnivores, but absent in birds and reptiles.
  • It consist of cortico spinal tract

• Extra pyramidal system
  • It is a complex network consisting of three important motor nuclei, red nucleus, vestibular nucleus and reticular formation and the inter-connecting tracts passing the motor signals from the motor cortex to the motor neurons of the spinal cord. This system generates gross involuntary movements by providing muscle tone of the extensor muscle and thereby regulates posture and locomotion.
  • Cortical activity descending in the extra-pyramidal pathways to the lateral vestibular nuclei of the brain stem (strong excitatory for spinal alpha -motor neurons) is primarily inhibitory.

  • This system is constituted by four major descending tracts - the reticulospinal, vestibulospinal, and rubrospinal and tectospinal tracts that leave the brain stem to influence the spinal motor neurons.