Makindo Medical Notes

Bony Anatomy

The bony spine, or vertebral column, is a central skeletal structure that supports the body, protects the spinal cord, and facilitates movement. It is composed of 33 vertebrae organized into five distinct regions.

Regions of the Spine

• Cervical Spine (C1-C7): The topmost section of the spine, consisting of seven vertebrae.
  • C1 (Atlas) and C2 (Axis) enable rotation and flexion of the head.
  • Supports the skull and allows a wide range of head movement.
• Thoracic Spine (T1-T12): The midsection of the spine, containing twelve vertebrae.
  • Attaches to the ribs, forming part of the thoracic cage.
  • Provides stability and protects thoracic organs, such as the heart and lungs.
• Lumbar Spine (L1-L5): The lower back section with five large vertebrae.
  • Supports the majority of body weight and allows for flexibility in bending and twisting.
• Sacral Spine (S1-S5): Five fused vertebrae forming the sacrum.
  • Connects the spine to the pelvis, providing stability for the upper body.
• Coccygeal Spine (Coccyx): The lowermost section, consisting of three to five fused vertebrae (coccyx or tailbone).
  • Provides attachment points for ligaments and muscles of the pelvic floor.

Structure of a Typical Vertebra

• Vertebral Body: The thick, cylindrical anterior portion that bears weight.
  • Each vertebra is separated by an intervertebral disc, which acts as a cushion and allows slight movement.
• Vertebral Arch: The posterior part of the vertebra, enclosing the spinal canal.
  • Includes pedicles and laminae that form the protective spinal canal housing the spinal cord.
• Processes:
  • Spinous Process: Projects posteriorly; serves as an attachment for muscles and ligaments.
  • Transverse Processes: Project laterally on each side; provide attachment points for muscles and ribs (in the thoracic spine).
  • Articular Processes: Superior and inferior facets allow for articulation with adjacent vertebrae, forming facet joints that enable movement and flexibility.

Function of the Bony Spine

• Support: Provides a central framework for the body, supporting the head, thorax, and upper body weight.
• Protection: Encloses and protects the spinal cord within the vertebral canal.
• Movement: Allows for flexibility and movement, with different regions enabling bending, twisting, and rotation.
• Shock Absorption: Intervertebral discs between each vertebra act as cushions, absorbing impacts and reducing stress on the spine.
• Attachment Points: Offers attachment sites for muscles and ligaments involved in posture, stability, and movement.

Nerves Anatomy

• Spinal nerves transmit information between peripheral body tissues and the spinal cord. A single pair of spinal nerves arises from each spinal cord segment.
• There are 31 pairs of spinal nerves: 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 1 coccygeal. Each pair is named for the spinal cord segment from which it arises. Spinal nerves are formed by the merging of (Fig. 3.24)
  • an anterior root carrying motor (efferent) fibres whose cell bodies are located in the anterior horn of the spinal cord, and
  • a posterior root carrying sensory (afferent) fibres whose cell bodies are located in a spinal ganglion located outside the spinal cord.
• Spinal nerves pass through the intervertebral foramina at the corresponding vertebral level.
  • Cervical nerves C1–C7 exit the vertebral canal superior to the vertebra of the same number (e.g., C4 spinal nerve exits between C3 and C4 vertebrae).
  • C8 spinal nerve exits below the C7 vertebra (between the C7 and T1 vertebrae).
  • Spinal nerves T1–Co1 exit the canal inferior to the corresponding vertebra.
• Because the spinal cord is shorter than the vertebral column, nerve roots from the lower spinal cord (L2–Co1) must descend below the conus medullaris within the lumbar cistern of the dural sac before exiting through the respective intervertebral foramina. This loose group of nerve roots within the dural sac is called the cauda equina

Summary

Cervical

Thoracic

Lumbar

Sacral

Skull

Cord

Segments

Disc

Cord C4

Cauda L4