Sensory pathways

• Sensory nerves carry a variety of senses triggered by peripheral stimuli (afferent)
• Somatic nerves are responsible for voluntary control of movement via skeletal muscle (efferent)
• Autonomic nerves are responsible for involuntary control of organs and tissues (efferent)
• Somatosensory information (spinal nerves)

  • pain
  • touch
  • pressure
  • temperature
  • proprioception
  • vibration
• Special sensory information (cranial nerves)

  • vision
  • hearing
  • taste
  • smell
  • balance
• Lateral spinothalamic tract carries sensory information about

  • pain
  • temperature
  • coarse touch
• Dorsal column carries sensory information about

  • proprioception
  • vibration
  • pressure
  • fine touch
• 3 neurones for somatosensory information

  • 1st order - soma in the dorsal root ganglion
  • 2nd order - soma in the spinal cord
  • 3rd order - soma in the thalamus
• Lateral spinothalamic tract carries contralateral sensory information.
• Dorsal column tract carries ipsilateral sensory information
• Lateral spinothalamic tract (pain, temperature, coarse touch)

  • 1st order neuron enters spinal cord via dorsal root
  • synapses in dorsal horn and crosses at spinal level
  • 2nd order neuron ascends on opposite side (CONTRALATERAL)
  • 3rd order neuron to cortex
• Dorsal column (proprioception, vibration, pressure, fine touch)

  • 1st order neuron enters via dorsal root and ascends on same side (ipsilateral)
  • 2nd order neuron synapses and crosses in medulla
  • 3rd order neuron to cortex
• What will result from unilateral damage to the cord (hemisection)?

  Fine touch is lost in the ipsilateral side below cord lesion
• Brown-Sequard syndrome - lesion is spinal cord which results in weakness or paralysis (hemiparaplegia) on one side of the body and a loss of sensation (hemianaesthesia) on the opposite side. May be caused by a spinal cord tumour, trauma, ischaemia or infectious or inflammatory disease (tuberculosis or multiple sclerosis)
• What will result from anterior spinal cord damage?

  Bilateral loss of pain
• Anterior spinal artery syndrome

  • most common cause of spinal cord infarction
  • caused by ischaemia of anterior spinal artery
  • results in loss of function on the most anterior 2/3 of the spinal cord
  • characterised by loss of pain and temperature sensation
• What will be affected first in an expanding central spinal cord lesion?

  Temperature
• Syringomelia

  • development of fluid-filled cyst within the spinal cord
  • cyst expands damaging the spinal cord
  • several causes: tumours, injuries and inflammation
  • symptoms: loss of sensitivity to pain and temperature
• What will be the consequence of irritating the trigeminothalamic tract?

  Contralateral face pain
• Trigeminal neuralgia

  • excruciating paroxysms of pain
  • one of the most severe pain types in clinical medicine
  • pain can occur spontaneously or when eating, talking, brushing teeth, touching face etc.
  • due to irritation of sensory fibres of trigeminal nerve
  • may be caused by tumours