Pathophysiology

• Why is the function of the bladder affected in spinal lesions?

  Spinal shock phase - autonomic activation signals to bladder & bowel can become blocked -> can lead to neurogenic bladder (depends on mechanism & site)

  Injury below pontine micturiation centre (brainstem) -> absent reflex -> bladder retention (not aware of bladder filling)

  After shock phase, some awareness of bladder filling can return

  Voluntary control over emptying the bladder will remain absent (incontience)
• Corticospinal tract

  Axons project down from motor cortex through the internal capsule -> through midbrain (cerebral peduncles) -> through ventral aspect of the medulla (pyramids) -> around 85% of fibres decussate -> run on contralateral side in the lateral funiculus (in spinal cord) -> synapses on primary motor neuron in the ventral horn Axons that don't decussate (around 15%) -> travel on ipsilateral side in ventral funiculus (spinal cord)
• What does a complete lesion present as?

  Both motor & sensory loss
• What is spinal cord shock?

  Temporary loss of all reflexes and paralysis below the level of spinal cord injury.
• Spinothalamic tract

  Pain, gross touch, temp

  Damaged tissue releases prostaglandins -> activation of nociceptors -> transduction (chemical -> electrical) -> AP generated on first order neuron -> travels through dorsal horn -> synapse with second order neuron in dorsal horn (spec. substantia gelatinosa), 1st order neuron releases substance P -> decuassation across spinal cord -> spinothalamic tract (anterolateral) -> up to thalamus -> synapse with third order neuron -> primary somatosensory cortex (S1)
• DCML tract

  Proprioception, vibration, light touch

  Conscious proprioception ->

  Proprioceptors detect tension -> project through dorsal column -> up to dorsal column nuclei -> projects to medial leminiscus -> medial leminiscus axons travel to the ventral posterior lateral nucleus of thalamus -> projects to primary somatosensory cortex (S1)

  In head, signals travel from trigeminal systems to ventral posterior medial nucleus of thalamus -> S1