Anatomy of the Spinal Cord

Vertebral Column:

  • Made up of vertebrae (boney parts) & discs (spongy material).
  • The vertebrae protect the spinal cord.
  • There are:
      7 Cervical vertebrae located in the neck
      12 Thoracic in the upper/mid back
      5 Lumbar in the lower back
      5 Sacral in the pelvis
      4 coccygeal (tailbone)
  • The sacral and coccygeal vertebrae are fused together.
  • Each vertebrae consists of a body & arch which form the vertebral foramen in which the spinal cord runs.
  • The discs sit between the vertebrae to provide cushioning and shock absorption.
  • Ligaments hold the vertebrae together and allow for movement.

Spinal Cord:

  • Looks like a rope. It is 18 inches long and approximately the width of the little finger.
  • Runs from the base of the brain to the lower part of the back around the L1 vertebrae level.
  • At the lower end of the spinal cord the nerves travel a long distance before exiting the spine. This is known as the cauda equina because is looks like a "horse's tail".
  • Provides communication between the brain and the body through the spinal nerves.

Spinal Nerves:

  • 31 pairs of anterior and posterior nerve roots emerge from the spinal cord.
  • The anterior nerve roots carry motor nerves.
  • The posterior nerve roots carry sensory nerves.
  • The anterior and posterior nerve roots join to form two spinal nerves, one on each side of the spine.
  • These become the peripheral nerves once they exit the intervertebral foramina.
  • There are 8 pairs of peripheral nerves (C1-C7) in the cervical column which exit from the spine on each side above the vertebrae with the same number.
  • The C8 nerve pair exits between the C7 and T1 bones.
  • There are 12 pairs of thoracic and 5 pairs of lumbar peripheral nerves which exit the spine on each side below the vertebrae with the same number.
  • There are 5 sacral and 1 coccygeal pair

Upper Motor Neurons:

  • The long nerve fibers inside the spinal cord are known as upper motor neurons (UMNs).
  • They run between the brain & the spinal nerves. 

Lower Motor Neurons:

  • The spinal nerves branch out from the spinal cord into the tissues of the body.
  • Spinal nerves are called lower motor neurons (LMNs).
  • The LMNs carry the messages to the muscles to coordinate movement. 

Motor Nerves:

  • The motor nerves carry messages related to movement from the spinal cord (UMNs) to the muscles.
  • Each motor nerve connects to a specific muscle, myotome.
  • Each level of the spinal cord causes movement in a certain group of muscles. 

Sensory Nerves:

  • The sensory nerves carry messages in different nerve fibers or spinal tracts.
  • Nerves in the body collect information and send it up the spinal cord to the brain.
  • They carry messages related to pain, touch, heat, cold, vibration, pressure, and knowledge of where a body part is in space.
  • Each sensory nerve collects information about feelings from a given body part or area of the skin known as a dermatome.  These match a specific spinal cord level. 

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