Spinal cord

• The spinal cord is a two-way conduction highway that conducts sensory input to the brain and motor output away from the brain
• Why Study the Spinal Cord

  • As an allied health professional it is important that you understand the anatomy and functions of the spinal cord to successfully assess, treat and rehabilitate patients with spinal cord injuries

  
• Spinal cord


  Long, thin, delicate tubular structure protected by the vertebral column

  
• Regions of the spinal cord

  • Cervical (C1-C8)
  • Thoracic (T1-T12)
  • Lumbar (L1-L5)
  • Sacral (S1-S5)
  • Coccygeal

  
• Spinal nerves


  • 8 Cervical nerves
  • 12 Thoracic nerves
  • 5 Lumbar nerves
  • 5 Sacral nerves
  • 1 Coccygeal nerve

  
• Dorsal root


  Contains the axons of sensory neurons
• Ventral root


  Contains the axons of motor neurons (somatic & autonomic)
• Cauda equina


  Collection of lumbar, sacral and coccygeal nerve roots that travel beyond the conus medullaris
• Structures that protect the spinal cord

  • Vertebral column
  • Cerebrospinal fluid
  • Spinal meninges
• Spinal meninges


  Continuous with the cranial meninges and extend beyond the spinal cord to the second sacral vertebra (S2)

  
• Epidural space


  Space between the outer dura mater and the vertebral column, site of anaesthetic administration
• Anterior median fissure


  Groove that divides the neural tissue of the spinal cord into a left and right side

  
• Posterior median sulcus


  Groove that divides the neural tissue of the spinal cord into a left and right side

  
• Gray matter


  Composed of neuron cell bodies (mainly), unmyelinated axons & neuroglia
• Gray commissure


  Site where axons cross from one side of the CNS to the other
• Subdivisions of gray matter

  • Posterior gray horns
  • Lateral gray horns
  • Anterior gray horns
• Posterior gray horns


  Contain sensory nuclei that receive and process incoming sensory input
• Anterior & lateral gray horns

  Contain motor nuclei that receive somatic or autonomic motor output
• White matter


  Composed of myelinated (mainly) & unmyelinated axons
• Subdivisions of white matter

  • Anterior white columns
  • Lateral white columns
  • Posterior white columns
• Ascending spinal cord tracts


  Conduct sensory input to the brain
• Ascending spinal cord tracts

  • Fasciculus gracilis
  • Fasciculus cuneatus
  • Lateral spinothalamic
  • Anterior spinocerebellar
  • Posterior spinocerebellar
  • Anterior spinothalamic

  
• Fasciculus gracilis & fasciculus cuneatus

  Conduct fine touch, vibration, light pressure and proprioception
• Lateral spinothalamic tract


  Conducts pain and temperature sensations
• Spinocerebellar tracts


  Conduct proprioception
• Anterior spinothalamic tract


  Conducts crude touch and deep pressure sensations
• Descending spinal cord tracts

  Conduct motor output from the brain
• Descending spinal cord tracts

  • Lateral corticospinal tracts
  • Anterior corticospinal tracts

  
• Lateral corticospinal tracts


  Conduct somatic motor output that controls the skeletal muscles of the limbs
• Anterior corticospinal tracts


  Conduct somatic motor output that controls the skeletal muscles of the trunk (axial skeleton)

  
• Somatosensory pathways


  Conduct general sensory input from receptors to the brain, involving a relay of first-order, second-order and third-order neurons
• Main somatosensory pathways


  • Spinothalamic pathway
  • Posterior column pathway (dorsal column-medial lemniscal pathway)
  • Spinocerebellar pathway
• from receptors to the brain

  1. Conduct motor output from the brain to skeletal muscles

  2. Consist of a chain of 2-3 neurons

  3. Usually cross over (decussate) within the CNS
• Somatosensory Pathways


  • Conduct general sensory input from receptors to the brain
  • Involve a relay of neurons called: first-order neuron, second-order neuron, third-order neuron
• Three main somatosensory pathways

  • Spinothalamic pathway
  • Posterior column pathway (a.k.a. dorsal column-medial lemniscal pathway)
  • Spinocerebellar pathway
• Spinothalamic Pathway


  1. Conducts sensations of crude touch, deep pressure, pain & temperature

  2. First-order neurons conduct sensory input from receptors into a posterior gray horn and synapse with second-order neurons within a sensory nucleus

  3. Second-order neurons conduct sensory input to the thalamus and ascend spinal cord in anterior spinothalamic tract (crude touch & deep pressure) or lateral spinothalamic tract (pain & temperature)

  4. Third-order neurons conduct sensory input to the primary somatosensory cortex (PSC)
• Posterior Column Pathway


  1. Conducts sensations of fine touch, light pressure, vibration & proprioception

  2. First-order neurons conduct sensory input into a posterior gray horn and up to the medulla oblongata, ascending spinal cord in a fasciculus gracilis or fasciculus cuneatus tract and synapsing with second-order neurons in the medulla oblongata

  3. Second-order neurons conduct sensory input to the thalamus and synapse with third-order neurons in the thalamus

  4. Third-order neurons conduct the sensory input to the PSC
• Spinocerebellar Pathway


  1. Conducts sensations of proprioception

  2. First-order neurons conduct sensory input from proprioceptors into a posterior gray horn and synapse with second-order neurons within a sensory nucleus

  3. Second-order neurons conduct sensory input to the cerebellum, ascending spinal cord in an anterior or posterior spinocerebellar tract
• Cerebellum


  • Uses proprioceptive information to maintain posture, balance, and ensure smooth, coordinated movements
• Somatic Motor Pathways


  1. Conduct somatic motor output from the primary motor cortex (PMC) to skeletal muscles

  2. Involve a relay of two neurons: upper motor neuron and lower motor neuron