Spinal chord

• Spinal chord is about 1 cm in diameter and generally decreases from anterior to posterior, with exceptions in the cervical and lumbar regions to accommodate for nerves to power the hands and feet
• Medullary pyramids


  Both major motor output paths go through this region on the surface of the medulla
• Corticobulbar tract


  M1 exit tract made up of axons that terminate in various brain stem motor nuclei, which communicate with cranial nerves, especially the ones with motor function CN V, VII, IX, XII
• Corticospinal tract


  M1 exit tract. Axons run through white matter of spinal chord.
• Lateral corticospinal tract = distal limbs contralateral voluntary movement. 90% . Anterior corticospinal tract = trunk muscles ipsilateral in brain stem but contralateral control. 10%
• Betz cells


  largest known neurons in the brain
• Monosynaptic reflex arc


  When a sensory motor synapses directly onto a motor neuron
• Central pattern generators (CPGs)


  Cell networks in charge of unconscious motor responses without brain or sensory inputs. Located in the brain stem (respiration) and the spinal chord (locomotion). Can be consciously overridden if we want to
• Pre-botzinger complex

  Breathing CPG in medulla
• Phrenic nerve

  Respiration
• Intercostal nerves

  Expand chest cavity
• Sleep apnea


  Possibly caused by issues in breathing CPGs
• Locomotion CPGs are very complex but can be carried out even when parts of the spine are severed