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Ligaments

The vertebral bodies are held firmly together by a combination of the intervertebral discs and the anterior and posterior longitudinal ligaments.

The anterior and posterior ligaments extend the whole length of the spine and are attached to each vertebral body and disc.

Other ligaments include:

  • Ligamentum Flavum - unites adjacent laminae, is elastic & joins adjacent lamina.
  • Supraspinatous - joins the tips of the adjacent spinous processes, is lax in the extended spine but taut in the flexed spine.
  • Interspinous - thin ligament connecting spinous processes along their adjacent borders.
  • Intertransverse - thin ligament of fibrous tissue connecting the transverse processes.

 

Muscles

The muscles of the back are divided into extrinsic and intrinsic muscles.  The function of the extrinscic muscles is mostly to connect and control of upper limb motion (i.e.  latissimus dorsi, levator scapulae, trapezius and rhomboids).

The function of the intrinsic muscles are to control movement of the spine and maintain posture.  They are further divided into three groups:

Group

Muscle Groups

Function

Superficial Layer

Splenius

Lie on the posterior aspects of the neck and control lateral and rotational movements of the head

Intermediate Layer

Erector spinae group

Large powerful muscle group that lies in the trough between the transverse processes.  The muscle group consists of:

  • Iliocostalis   (lateral column)
  • Longissimus (intermediate column)
  • Spinalis  (medial column)

Bilateral action

  • Extends spine
  • Controls flexion so to permit smooth movements

Unilateral action

  • Lateral bend of spinal column

Deep Layer

Transversospinal group

Lies deep to erector spinae group and conprise of three main muscles:

  • Semispinalis
  • Multifundus
  • Rotatores

Multipennate muscles that control movements of individual vertaebrae.

 

 

From a practical point of view the principle muscles producing movements of the thoraciclumbar spine are:

 

Movement

Muscles

Flexion

Rectus abdominus

Psoas major

Extension

Erector spinae

Multifundus

Semispinalis thoracis

Lateral

Liocoastalis thoracis

Lumbordum

Longissimus thoracis

Multifundis

External and internal oblique

Quadraus lumborum

Rotation

Rotatores

Multifidus

External oblique

Semispinalis thorasis

 

 

Spinal cord and nerve roots

The spinal cord from the foramen magnum to the level of the first lumbar vertebrae where it forms the cone shaped conus medullaris.

There are 31 bilateral nerve roots:

            8          Cervical

            12        Thoracic

            5          Lumbar

            5          Sacral

            1          Coccygeal

 

As the skeletal elements have grown faster that the respective neural elements the spinal cord in adult life ends at the level of L1.  As a consequence the lower spinal nerve roots (L2-S5) have a much longer distance to travel to exit the spinal canal.

Spinal nerve root exit the spinal canal through intervertebral foramen below the level of their respective skeletal elements (i.e.  L5 nerve root will exit at the L5 / S1 foramen).

The spinal cord and nerve roots are further protected by the surrounding meninges and cerebrospinal fluid.

The meninges is made up of three layers:

Dura

  • Strong fibroelastic tissue.
  • Outer most layer.
  • Extends from base of skull to the coccyx.
  • Separated from the periosteum of the vertebral column by the epidural space.

 

Arachnoid

  • Much weaker fibroelastic material compared to dura matter.
  • Covers and blends with the spinal nerves.
  • Separated from the pia mater on its inner surface bt the subarchnoid space.

 

Pia

  • Most intimate and innermost connection to the spinal cord and nerve roots.
  • Relatively loose and fine connective tissue that also covers the spinal cord vasculature.