Tectospinsl Tract

  • Origin: Dorsal part of midbrain, which is behind aqueduct (central canal) of midbrain, is called Tectum. When viewed from behind, tectum is seen to be made up of one upper and one lower pair of bulges called superior and inferior colliculi (Singular-colliculus). These colliculi are made up of clusters of nerve cells which are arranged in the form of superficial, intermediate and deep layers.
    Tectospinal tract originates from intermediate and deep layers of cells of superior colliculus of both sides at the upper half of midbrain.
  • Nature: Tectospinal tract is crossed tract like rubrospinal tract. Fibers of this tract also crosshorizontally in front of aqueduct of midbrain, in a more posterior plane, just after their origin from tectum. It is called dorsal tegmental decussation.

    After decussation, fibers of this tract descend through central core (tegmentum) of brainstem to reach the level of spinal cord.

  • Localization: Tectospinal tract is localized in anterior white column of spinal cord, in front of anterior corticospinal tract, just by the side of ventral part of anterior median fissure.
  • Termination: Tectospinal tract extends only upto upper cervical segments of spinal cord.
    Before terminating into alpha and gamma motor neurons of spinal cord, fibers form polysynaptic connection via interneurons of laminae VI to VIII.
  • Functions: Before the function of tectospinaltract is understood, it is to be noted that, this tractforms efferent component of a reflex pathway known as spinovisual reflex. Activity of this pathway is manifested by turning neck with head away when a powerful light falls on retina of eyeball.

5 components of this reflex pathway are following:
  1. Receptor: Rod and cone cells of retina (photoreceptors)— which are stimulated by light falling on retina.
  2. Afferent path: Visual pathway from retina – optic nerve – optic chiasma – optic tract – lateral geniculate body – superior brachium.
  3. Center: Superior colliculus of midbrain which receives collaterals from lateral geniculate body through superior brachium.
  4. li>Efferent path: Tectospinal tract.
  5. Effector: Voluntary muscles of neck.

Source: Easy and Interesting Approach to Human Neuroanatomy (Clinically Oriented) (2014)