Chapter 13 (1)

• Spinal cord


  Cylinder of nervous tissue that arises from the brainstem at the foramen magnum of the skull, occupies the upper two-thirds of vertebral canal, inferior margin ends at L1 or slightly beyond, averages 1.8 cm thick and 45 cm long, gives rise to 31 pairs of spinal nerves

  
• Segment


  Part of the spinal cord supplied by each pair of spinal nerves

  
• Spinal cord


  • Conduction - nerve fibers conduct sensory and motor information up and down the spinal cord
  • Neural integration - spinal neurons receive input from multiple sources, integrate it, and execute appropriate output (e.g., bladder control)
  • Locomotion - spinal cord contains central pattern generators: groups of neurons that coordinate repetitive sequences of contractions for walking
  • Reflexes - involuntary responses to stimuli that are vital to posture, coordination and protection
• Anterior median fissure


  Longitudinal groove on anterior side of spinal cord

  
• Posterior median sulcus


  Longitudinal groove on posterior side of spinal cord
• Regions of the spinal cord

  • Cervical
  • Thoracic
  • Lumbar
  • Sacral

  
• Cervical enlargement


  Thicker part of the spinal cord where nerves to the upper limb originate
• Lumbar enlargement


  Thicker part of the spinal cord where nerves to the pelvic region and lower limbs originate

  
• Medullary cone (conus medullaris)


  Spinal cord tapers to a point inferior to lumbar enlargement

  
• Cauda equina


  Bundle of nerve roots that occupy the vertebral canal from L2 to S5

  
• Meninges


  Three fibrous membranes that enclose the brain and spinal cord: dura mater, arachnoid mater, and pia mater
• Epidural space


  Space between the dura mater and the vertebrae

  
• Subarachnoid space


  Space between the arachnoid mater and the pia mater, filled with cerebrospinal fluid (CSF)
• Lumbar puncture (spinal tap)


  Procedure to take a sample of cerebrospinal fluid
• Pia mater


  Delicate membrane that follows the contours of the spinal cord

  
• Spina bifida


  Congenital defect in which one or more vertebrae fail to form a complete vertebral arch for enclosure of the spinal cord

  
• Spina bifida cystica


  Most serious form of spina bifida
• Folic acid (a B vitamin now added to flour) is part of a healthy diet for all women of childbearing age – it reduces risk of spina bifida
• Gray matter


  Neuron cell bodies with little myelin, site of information processing and synaptic integration
• White matter


  Abundantly myelinated axons that carry signals from one part of the CNS to another
• Posterior (dorsal) horn


  Part of the gray matter of the spinal cord
• Posterior (dorsal) root


  Carries only sensory fibers
• Anterior (ventral) horn


  Part of the gray matter of the spinal cord
• Anterior (ventral) root


  Carries only motor fibers
• Gray commissure


  Connects the right and left sides of the gray matter
• Central canal


  Lined with ependymal cells and filled with cerebrospinal fluid
• Lateral horn


  Part of the gray matter visible from T2 through L1, contains neurons of the sympathetic nervous system
• Funiculi


  Three pairs of white matter bundles: posterior (dorsal), lateral, and anterior (ventral)
• Tracts or fasciculi


  Subdivisions of each funiculus
• Ascending tracts


  Carry sensory information up the spinal cord
• Descending tracts


  Carry motor information down the spinal cord
• Decussation


  Crossing of the midline that occurs in many tracts
• Contralateral


  When the origin and destination of a tract are on opposite sides of the body
• Ipsilateral


  When the origin and destination of a tract are on the same side of the body
• Ascending tracts


  • Gracile fasciculus
  • Cuneate fasciculus
  • Spinothalamic tract
  • Spinoreticular tract
  • Posterior (dorsal) and anterior (ventral) spinocerebellar tracts

  
• Gracile fasciculus


  Carries signals from midthoracic and lower parts of body, below T6 it composes the entire posterior funiculus
• Cuneate fasciculus


  Occupies lateral portion of posterior funiculus at T6 and above, carries signals from upper limb and chest

  
• Medial lemniscus


  Tract leading from gracile and cuneate nuclei to thalamus
• Spinothalamic tract


  Part of the anterolateral system, carries signals for pain, pressure, temperature, light touch, tickle, and itch
• Spinoreticular tract


  Travels up anterolateral system, carries pain signals resulting from tissue injury