Motor pathways in spinal cord and motor deficiencies in spinal cord lesions

Motor pathways

  1. Pyramidal tracts: originate in the cerebral cortex and is responsible for the voluntary control of all body muscles. Those tracts go through the pyramids of the medulla.
    • Corticospinal tract.
    • Corticonuclear tract.
  2. Extrapyramidal tracts: originate in the brainstem/midbrain and is responsible for involuntary control of muscles for muscle coordination and posture purposes. Those tracts go through the tegmentum instead.
    • Reticulospinal tract.
    • Rubrospinal tract.
    • Vestibulospinal tract.
    • Tectospinal tract.
Tectum and Tegmentum - Kenhub

Pyramidal Tracts

Refer to the article concerning this here.

Extrapyramidal Tracts

  • The extrapyramidal system involves the action of the basal ganglia and their modulation of motor movement via direct and indirect pathways. The output is conveyed by the 4 tracts mentioned above.
  • Reticulospinal tract:
    • Divided into medial and lateral reticulospinal tracts.
    • Medial reticulospinal tract:
      • Originate in the pontine reticular formation and descend ipsilaterally.
      • Goes to the medial part of the ventral funiculus of spinal cord.
      • Innervates alpha and gamma motor neurons of extensors and antigravity muscles.
    • Lateral reticulospinal tract:
      • Originate in the medullary reticular formation and some descend contralaterally.
      • Goes to the lateral part of the ventral funiculus of spinal cord.
      • Innervates interneurons in the intermediate zone of gray matter. Those neurons inhibit the function of alpha and gamma motor neurons.
    • Function might be to reduce stiffness of antigravity muscles and maybe aid in breathing by innervating intercostal and phrenic nerve nuclei.
  • Vestibulospinal tract:
    • Divided into medial and lateral vestibulospinal tracts.
    • Medial vestibulospinal tract:
      • Originates in the medial vestibular nucleus (Schwalbe’s nucleus) in the medulla.
      • Descends down and send impulses to nuclei that innervate upper limb and neck muscles.
    • Lateral vestibulospinal tract:
      • Originates in the lateral vestibular nucleus (Deiter’s nucleus) in the pons.
      • Sends fibers ipsilaterally to nuclei that innervate extensor muscles for posture and balance.
    • Function is maintaining right posture and preparing and controlling the posture of the body before making a specific movement. Also, while moving, these tracts synchronize the movement with maintaining posture.
  • Rubrospinal tract:
    • Originates from the red nuclei in the midbrain.
    • Descends contralaterally to the spinal cord and go ventrolaterally where they terminate in laminae V to VII and innervate the nuclei of flexor muscles.
    • Maintain muscle tone of flexors.
  • Tectospinal tract:
    • Originate in the superior colliculus of the tectum of midbrain and then descend to terminate on the contralateral laminae VI to VIII in cervical and upper thoracic spinal cord.
    • It synapses on neurons that innervate head and neck muscles.
    • The superior colliculus also receives visual and auditory stimuli so this tract is involved in the movement of the body in response to visual and auditory stimuli.
Spinal Cord Cross-Section Ascending and Descending Tracts - Wikipedia
Spinal Cord Cross-Section Ascending and Descending Tracts - Wikipedia

Motor deficiencies in spinal cord lesions

  • Anterior horn lesions:
    • Lesion to alpha and gamma motor neurons (lower motor neurons):
      • Flaccid paralysis: weakness and decreased muscle tone.
      • Hypotonia: decreased muscle tone.
      • Hyporeflexia: decreased reflex response.
      • Fasciculations: muscle twitches.
    • Important Note: lesions to lower motor neurons ONLY affect the muscles that are innervated by those neurons. So, let’s say the lesion is in the cervical region; the muscles affected will be upper limb muscles; lower limb muscles WILL NOT be affected.
  • Lesions to motor tracts (corticospinal tract):
    • Symptoms will appear in ALL SEGMENTS below the lesion since the tract itself is damaged at a particular segment.
  • Brown-Sequard syndrome is caused by the damage of half of the spinal cord (hemisection). This causes loss of coordination, proprioception, and discriminative touch on the ipsilateral side of the body, and temperature, pain, and pressure sensations on the contralateral part of the body 1-2 segments below the lesion (Lissauer’s tract) AND you’ll have a lesion in the corticospinal tract, so motor deficiencies will appear in all segments below the lesion.