Spinal Cord Anatomy

Spinal Cord Structure

• The spinal cord is a long, slender cylinder of nerve tissue that extends from the brain stem, measuring about 45cm in length and 1-1.5cm in width.
• It is protected by the vertebral column and descends through the vertebral canal, exiting through a large hole in the base of the skull.

Spinal Nerves

• There are 31 pairs of spinal nerves, named according to the region of the vertebral column from which they emerge.
• The pairs include:
  • Cervical nerves (8 pairs, C1-C8)
  • Thoracic nerves (12 pairs, T1-T12)
  • Lumbar nerves (5 pairs, L1-L5)
  • Sacral nerves (5 pairs, S1-S5)
  • Coccygeal nerves (1 pair)

Differential Growth

• During development, the vertebral column grows 25cm longer than the spinal cord.
• As a result, the spinal cord segments giving rise to spinal nerves are not aligned with the corresponding intervertebral spaces.
• Most spinal nerves descend before emerging from the vertebral column at the corresponding space.
• The spinal cord extends only to the L1-L2 vertebra level (waist level).

Spinal Cord Grey Matter

• The grey matter is centrally located, functionally organized, and forms an inner butterfly-shaped region surrounded by outer white matter.
• The grey matter consists of neuronal cell bodies, dendrites, and glial cells.
• The central canal lies in the center of the grey matter and is filled with cerebrospinal fluid.
• Each half of the grey matter is divided into:
  • Dorsal (posterior) horn: contains cell bodies of interneurons that receive sensory information
  • Ventral (anterior) horn: contains cell bodies of efferent motor neurons supplying skeletal muscles
  • Lateral horn: contains cell bodies of autonomic nerve fibers supplying smooth muscles, cardiac muscles, and exocrine glands

Spinal Cord White Matter

• The white matter is organized into tracts, consisting of bundles of nerve fibers (axons of long interneurons) with similar functions.
• Tracts are grouped into columns that extend the length of the spinal cord.
• Tracts begin or end within a particular brain area and transmit specific types of information.
• There are two main types of tracts:
  • Ascending tracts (cord to brain): transmit signals derived from afferent input
  • Descending tracts (brain to cord): relay messages from the brain to efferent neurons
• Tracts are named based on their origin and termination.

Injury and Function

• Damage to particular areas of the spinal cord can interfere with some functions while leaving others intact.
• Various types of signals are carried in different tracts within the spinal cord.