Spinal cord tracts


tracts

1. Ascending tracts

Fasciculus gracilis

  • Carries nerve fibers of the dorsal column-medial lemniscus pathway from the lower limbs and trunk.
  • Transmits conscious proprioception, vibration and fine touch sensations.

Fasciculus cuneatus

  • Carries nerve fibers of the dorsal column-medial lemniscus pathway from the upper limbs and trunk.
  • Transmits proprioception, vibration and fine touch sensations.

Anterior spinothalamic tract

  • Transmits pressure and crude touch sensations from tactile corpuscles and hair follicles.

Lateral spinothalamic tract

  • Transmits pain and temperature sensations.

Anterior and posterior spinocerebellar tracts

  • Transmit unconscious proprioceptive signals from muscle spindles and tendon receptors.
  • Projection fibers in the anterior tract transmit to both ipsilateral and contralateral cerebellum through the superior cerebellar peduncle.
  • Projection fibers in the posterior tract transmit strictly to ipsilateral cerebellum through the inferior cerebellar peduncle.

Spino-olivary tract

  • Carries fibers that transmit unconscious proprioceptive signals from contralateral muscle spindles and tendons as well as cutaneous signals to inferior olivary nucleus.
  • It is involved in balance and control of movements of the extremities and trunk.

2. Descending tracts

I. Pyramidal tracts

Anterior corticospinal tract

  • Transmits pyramidal fibers that control the axial muscles.
  • Composed of corticospinal fibers that do not decussate in the pyramids (\~20%).
  • Most fibers cross at the segmental level to synapse in the contralateral anterior horn.

Lateral corticospinal tract

  • Transmits pyramidal fibers that control the muscles of the extremities.
  • Composed of corticispinal fibers that decussate in the pyramids (\~80%).

II. Extrapyramidal tracts

Tectospinal tract

  • Transmits fibers originating from the superior colliculus in the midbrain tectum to the cervical spinal cord.
  • Mediates motor impulses to contralateral musculature.
  • Responsible for reflex postural movements of the head in response to visual and auditory stimuli.

Medial (pontine) and Lateral (medullary) reticulospinal tracts

  • The MRT mediates motor signals to extensor (antigravity) muscles.
  • The LRT is responsible for automatic breathing and mediates inhibitory signals to axial extensor muscles.
  • The reticulospinal tracts influence muscle tone, coordinate postural and locomotive activities, mediate autonomic functions and have pain modulating role.

Rubrospinal tract

  • Originates in the red nucleus and its fibers cross over in the midbrain.
  • Facilitates flexion and regulates flexor tone.
  • Mediates voluntary movement in large muscles as well as fine motor control, mainly in the upper extremity.

Olivospinal tract

  • Its existence is disputed.
  • Originally thought to carry fibers descending from inferior olivary complex to cervical spinal cord.