VAN 121: Veterinary Gross Anatomy-II (2+2)

TRACTS IN VENTRAL WHITE COLUMN

Ascending tract

• Ventral spino -thalamic tract:
  • This ascending tract consists of fibres derived from the sensory neurons of dorsal gray column, which ascend directly upto two or three segments and then cross to the opposite side to reach the ventral white column.
  • They pass up to the thalamus, from where they are relayed to the sensory area of cerebral cortex. This tract conveys coarse touch and pressure sensations.

Descending tract

• Vestibulo-spinal tract:
  • It arises from the vestibular nuclei in the medulla oblongata and ends around the motor neurons of ventral gray column.
  • This serves as an efferent pathway for impulses from the vestibular organ and for bringing about coordination of body musculature in the maintenance of equilibrium, etc.
• Reticulo-spinal tract:
  • The fibres arise from the cells in the reticular formation of brain stem, descend in the ventral white column and end in synaptic relations with the somatic motor neurons in the ventral gray column and also with the visceral motor neurons in the lateral gray column.
  • This tract serves as a pathway for
    • Autonomic or visceral efferents from hypothalamic centres and other areas of the brain
    • Regulation of reflex activity of skeletal muscles (facilitating and inhibiting reflexes, regulation of rhythmic activity of muscles as in respiration etc.) 
    • Adjustment of threshold for transmission of sensory impulses.

• Intersegmental tract:
  • The remaining part of the column constitutes this tract. It connects different segments and some fibres go to form the median longitudinal bundle.