D3 - Medulla spinalis, the spinal segment, formation of the spinal nerve

Question 1

Medulla spinalis

Answer 1

• Medulla spinalis = spinal cord
• Medulla spinalis: A thick cord of nerve tissue which is a major part of the vertebrate central nervous system. It extends from the brainstem down through the spine, with nerves branching off to various parts of the body. It is enclosed in and protected by the vertebral column
• At the cervical intumescence the cord is widened for the formation of the brachial plexus
• At the lumbar intumescene the cord is widened for the formation of the lumbosacral plexus
• The spinal cord tapers into a conus medullaris caudal to the lumbar enlargement which is finally reduced to form the terminal filament
• The spinal cord can be divided into:
  
  • Cervical spinal cord
  • Thoracic spinal cord
  • Lumbar spinal cord
  • Sacral spinal cord
  • Coccygeal spinal cord
• The spinal cord is divided itno two symmerical halves by
  
  • Sulcus medianus dorsalis
  • Fissure mediana ventralis
• As the growth of the spinal canal is greater than that of the spinal cord, some of the spinal segments do not correspond with the vertebrae. This is the reason why the spinal roots of the last lumbar spinal segments, and the sacral and caudal spinal roots, extend caudally to reach the corresponding vertebral foramin
• Inside the vertebral canal, they arrange around the terminal filament, and form the cauda equina

Question 2

The spinal segment

Answer 2

• Dorsal spinal root: Afferent fibers, sensory.
  
  • Enters the spinal cord
  • Dorsolateral sulcus
  • Spinal ganglia: located within each dorsal root, and contains sensory neuros (ø first cervical nerve)
• Ventral spinal root: Efferent, motor
  
  • Leaving the spinal cord
  • Ventrolateral sulcus
• The nerve fibers of each root are bound together at the for. intervertebralis where they join to form the spinal nerve
• The spinal cord is not segmented, but can be divided into segements based on the spinal nerves
  
  • ​Each pair of spinal nerves is responsible for the innervations of a body segment
• Spinal nerves have to pass caudally to leave at their appropirate intervertebral foramina
  
  • ​Reason: During foetal development the vertebral column increases more in length than the spinal cord and the caudal end of the spinal cord is cranial to the caudal end of the vertebral column
• Cauda equine: Sacral and caudal spinal roots stream caudally beyond the conus medullaris

Transverse section of spinal cord:

• Grey matter
  
  • ​Compesed of cell bodies
  • Divided into:
    
    • Dorsal horn/column​
      
      • ​Somatic and afferent visceral neurons
    • Lateral horn/column
      
      • ​Symp. and parasymp. inntervation of viscera
    • Ventral horn/column
      
      • ​Mainly motor neurons
• White matter
  
  • ​Surrounds the grey matter
  • Divided into:
    
    • Dorsal column/funiculi
      
      • ​All white matter between the dorsal median sulcus and the line of origin of the dorsal root of the spinal nervex
      • Ascending spinal tract
    • Ventral column/funiculi
      
      • ​Between dorsal and ventral spinal roots, and continues to the ventral median fissure
      • Descending motor nerve tract

Question 3

Formation of the spinal nerve

Answer 3