Spinal cord and spinal nerves

• The central nervous system is made up of the brain and the spinal cord
• In this chapter, the focus is on the spinal cord
• Functions of the spinal cord

  • Processes reflexes
  • Processes excitatory and inhibitory postsynaptic potentials
  • Integrates information
  • Transmits sensory information to the brain and motor information from the brain
• Reflex processing in the spinal cord

  1. Sensory information received

  2. Reflex processed in the spinal cord

  3. Automatic response occurs
• Reflexes processed in the spinal cord are faster than those processed in the brain
• Excitatory postsynaptic potential (EPSP)

  Cell is depolarized and closer to threshold
• Inhibitory postsynaptic potential (IPSP)


  Cell is hyperpolarized and moved away from threshold
• The spinal cord integrates EPSPs and IPSPs
• The spinal cord acts as a highway, transmitting sensory information to the brain and motor information from the brain
• Transmission of information through the spinal cord

  1. Sensory receptors in skin send information to spinal cord

  2. Spinal cord transmits sensory information to brain

  3. Brain sends motor information to spinal cord

  4. Spinal cord transmits motor information to nerves and muscles
• The spinal cord is surrounded by layers of protection: vertebral bones, meninges, and cerebrospinal fluid
• Meninges


  Connective tissue coverings of the spinal cord, consisting of the dura mater, arachnoid mater, and pia mater
• The spinal cord begins as an extension of the medulla oblongata and ends around the L2 vertebra
• Below the L2 vertebra, there is a collection of nerves called the cauda equina
• The spinal cord has a cross-sectional appearance with a central grey matter region and surrounding white matter
• Grey matter


  Contains unmyelinated neurons that transmit information more slowly
• White matter


  Contains myelinated neurons that transmit information more quickly
• The anterior median fissure is a deep groove on the anterior side of the spinal cord
• Posterior horns


  Pointy projections of grey matter on the posterior side of the spinal cord
• Anterior portion of the spinal cord

  Has a deep groove in the middle called the anterior median fissure
• Posterior portion of the spinal cord

  Does not have a deep groove
• Posterior horns


  • Two pointy projections towards the back of the spinal cord
• Anterior horns


  • Two pointy projections towards the front of the spinal cord, on the same side as the anterior median fissure
• Lateral horns


  • Two small, subtle bumps on the sides of the spinal cord
• Posterior/dorsal horns


  Carry sensory information
• Anterior/ventral horns


  Carry motor information
• Posterior root


  Branch coming off the posterior/dorsal horn, has a ganglion (collection of neuron cell bodies)
• Anterior root


  Branch coming off the anterior/ventral horn, does not have a ganglion
• Spinal nerve


  Formed by the merger of the anterior and posterior roots, carries both motor and sensory information
• There are 31 pairs of spinal nerves
• Descending tract/motor tract


  Pathway for sending motor information from the brain down the spinal cord
• Ascending tract/sensory tract


  Pathway for sending sensory information from the spinal cord up to the brain
• Endoneurium


  Connective tissue covering a single axon
• Perineurium


  Connective tissue covering a fascicle (collection of axons)
• Epineurium


  Connective tissue covering the entire nerve
• Rami


  Branches of nerves off the spinal cord
• Plexus


  Collection of spinal nerves
• Plexuses


  • Cervical plexus
  • Brachial plexus
  • Lumbar plexus
  • Sacral plexus
• Spinal nerves are named with a letter (indicating the plexus) and a number (indicating their position in the plexus)
• Cervical plexus


  Collection of nerves coming off the spinal cord in the neck region