Lecture Notes: Spinal Cord Tracts

Overview

• The spinal cord contains several distinct tracts divided into:
  • Ascending tracts (sensory)
  • Descending tracts (motor)
• White matter: Composed of tracts, named for the myelin around axons.
• Gray matter: Centrally located, includes the ventral and dorsal horns.

Ascending Tracts (Sensory Pathways)

• Function: Transport information from the body to the brain.
• Color Coding: Sensory tracts are represented in blue.

Dorsal Column (Posterior Column)(transmiting consious sensation)

• Fasciculus Cuneatus & Fasciculus Gracilis
  • Responsible for fine touch, tactile sensation, vibration, and proprioception.
  • Fasciculus Gracilis (medial): Carries signals from lower limbs (below T6).
  • Fasciculus Cuneatus: Carries signals from upper limbs (T6 and above).
  • Pathways run ipsilaterally in the spinal cord and decussate in the medulla.
  • Injury Impact: Leads to ipsilateral loss of fine touch, vibration, proprioception.
• Terminate in nucelus cunetus and nucleus gracillus of medulla

Anterolateral Pathways(same)

• Anterior Spinothalamic Tract
  • Responsible for crude touch and pressure.
• Lateral Spinothalamic Tract
  • Responsible for pain and temperature.
  • Both Decussate within the spinal cord, causing contralateral loss of pain ,pressure,temperature due to lesions of spinal cord.
  • Note: Nerves may ascend 1-2 levels before crossing.

Other Sensory Pathways

• Anterior & Posterior Spinocerebellar Tracts(uncrossed)
• Spino-olivary Tract
  • Carry unconscious proprioceptive information to cerebellum.(lower limb,trunk )
• Origin lateral(ventral, dorsal part of funniculus)
• Cuneocerebellar & Rostral Spinocerebellar Tracts
  • Carry proprioceptive signals from upper limbs and neck.

Descending Tracts (Motor Pathways)

All terminate in ventral horn

• Function: Responsible for muscle movement.

Pyramidal Tracts

• Anterior & Lateral Corticospinal Tracts
  • Involved with voluntary limb movement.
  • Lateral Corticospinal Tract: Decussated fibers, cross at the medulla.
  • Anterior Corticospinal Tract: Decussate at the spinal cord level they innervate.(axial muscles)

Extrapyramidal Tracts

• Rubrospinal Tract(lateral)
  origin is red nucleus if mid brain.
  • Provides contralateral innervation, (crosses in mid brain)involved in fine motor control.(flexor muscles)
• Reticulospinal Tracts
  • Medial Reticulospinal Tract: Facilitates voluntary muscle contraction, increases tone.
  • Lateral Reticulospinal Tract: Inhibits voluntary movement, reduces muscle tone, aids automatic breathing.
• Vestibulospinal Tract(uncrossed if lateral)
  origin: vestibonuclei in medulla
  • Controls balance and posture.
• Tectospinal Tract
• Superior collicus origin in mid brain
  • Coordinates head movements with vision.