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Vertebral Column: Regions & Curvatures M1 – Gross and Developmental Anatomy Vertebral Column, Spinal Cord, and Deep Back Dr. Krieg Vertebral Column = Stack of Articulated Vertebrae •Synovial Joints between articular facets •Intervertebral disks between vertebrae •Spinal nerves exit vertebral canal via Intervertebral foramina Prenatal C-Shaped Curvature Infant is born with curvatures which are concave anteriorly in all regions of the spine. Secondary Curvatures Develop in Cervical and Lumbar Regions •As infant raises head to look around, cervical curvature develops concave posteriorly. •Standing upright requires lumbar curvature concave posteriorly. •Abnormal Curvatures: •Kyphosis: exaggerated thoracic curvature resulting in humping over •Lordosis: accentuation of lumbar curvature concave posterior •Scoliosis: Curvature to the side Anterior Longitudinal Ligament •Located Anterior to the vertebral bodies •Resists Extension of the spine (bending backward) Parts of a Typical Vertebra •Body •Arch: •Pedicle •Lamina •Processes •Transverse •Spinous •Articular facets •Superior •Inferior •Vertebral Foramen Posterior Longitudinal Ligament •Located Posterior to the vertebral bodies •Located Anterior to the spinal cord •Resists Flexion of the spine (bending forward) Ligamenta Flava •Atlas 12th ed, fig 4.24, p. 302 •Attached to laminae of contiguous vertebrae •Prevent excessive flexion •Pierced by spinal tap needle Supraspinous & Interspinous Ligaments •Supraspinous ligaments lie Posterior to spines, as if a strip of “scotch tape” were applied •Interspinous ligaments lie between the spinous processes •Both resist flexion Disks are Shock Absorbers •Shape of disks changes as force is applied •Fluid nucleus pulposus is incompressible •Force is distributed equally in all directions, preventing undue concentration of stress anywhere on the vertebral body Capsular Ligaments •Surround the joints between superior and inferior articular processes •Are generally lax to permit free gliding movements •Note the intervertebral disks between the bodies of the vertebrae Intervertebral Disks •Anulus fibrosis: fibrocartilaginous outer ring •Nucleus pulposus: semi-gelatinous fluid mass surrounded by anulus fibrosus •Reinforced by anterior and posterior longitudinal ligaments •Least reinforcement posteriolaterally Atlantooccipital and Atlantoaxial Joints •Base of skull is formed by the Occipital Bone •1st vertebra = Atlas •2nd vertebra = Axis •Atlantooccipital joint allows flexion and extension: i.e., the “yes” joint •Atlas pivots around dens of axis hence is the “no” joint Atlantoaxial Joint Movements of the Spine are the Sum of Movements between Vertebrae Flexion Dens represents the body of the Atlas Extension Lateral Bending Anterior arch and Transverse Ligament of Atlas form pivot around the dens Deep (True) Back Muscles Splenius Muscles •Extend the back •Located deep to Thoracolumbar Fascia, within a tight fascial space •Developed in Back, not immigrants •Innervated Segmentally by Dorsal Primary Rami •Organized in Longitudinal (Erector Spinae) and Transversospinal Groups •Each group comprised of 3 major subgroups, also with regional specializations •Relationship of trapezius to splenius: Atlas, 12th ed. Fig 4.29, p. 308 •Distinctive fiber direction: diagonally upward and laterally •Splenius Capitis is superior, and inserts into skull •Splenius Cervicis inserts on cervical transverse processes •Acting unilaterally, both muscles rotate face to same side; left and right act together to extend neck Erector Spinae •Origin: sacrum, iliac crest, vertebral spines •3 columns •Iliocostalis (lateral) inserts on ribs •Longissimus (middle column) inserts on transverse processes •Spinalis: (medial column) inserts on spines of vertebrae Transversospinalis Group Rotate body to opposite side Semispinalis muscle Fig. 4.32 Grant’s Atlas Multifidus •Semispinalis is absent in the lumbar region. •Multifidus is prominent in lumbar region •Anterior and posterior layers of lumbar fascia form compartment around erector spinae (removed) and transversospinal muscles. Rotatores brevis Rotatores longus Fig. 4.34 Grant’s Atlas Suboccipital Region •2 rectus, 2 oblique muscles •C1 motor to the 4 muscles •C2 cutaneous (the Greater Occipital nerve) •Splenius & semispinalis capitis = roof •Semispinalis cervicis ends at C2 spine •Vertebral artery supplies brain Meninges: 3 layers covering CNS From Outside in: •Epidural Space •Dura (tough) 1 •Subdural Space •Arachnoid (spidery) •Subarachnoid Space (CSF) •Pia (tender) Dura Mater Arachnoid Mater (spidery mother) Tube of tough collagenous tissue that covers cord and cauda equina Middle layer of meninges Continuous with dura of brain and extends to S2 vertebra Smooth where it contacts dura Below S2 the dura is reduced to a slender strand which connects to the coccyx. Thin, filmy, spider-web like extensions attach to pia THE SUBARACHNOID SPACE ENDS HERE. Dural sleeves extend out around the spinal nerves to blend with the perineurium on the peripheral nerves Bounds the subarachnoid space which contains cerebrospinal fluid Pia Mater (tender mother) Ventral Rootlets •Innermost covering of cord •Closely bound to cord and nerve rootlets as they cross the subarachnoid space •Denticulate ligaments are specializations of pia which anchor the spinal cord laterally to the dura, and is most important to preventing lateral and AP displacement of the spinal cord •Dorsal and ventral rootlets pass on dorsal and ventral sides, respectively. Fig. 4.43A Grant’s Atlas Conus medullaris Filum terminale internum Dura mater Cauda equina Filum terminale externum Fig. 4.42 Grant’s Atlas Fig. 4.43A Grant’s Atlas 12th ed. Epidural Space Contains the Internal Vertebral Plexus Fig. 4.43C Grant’s Atlas Filum terminale internum (Pia) •Internal venous plexus is within vertebral canal, in the epidural space Filum terminale •External plexus is outside vertebral canal •Longitudinal vessels can spread disease from pelvis to cranium •Segmental veins exit at each level Spinal Cord •Spinal cord is initially the same length as the vertebral column •One pair of spinal nerves exits at each vertebral level •Growth of vertebrae outpaces that of cord •Adult cord ends at L2 • Cord segments located higher than vertebra where nerves exit: S1S5 segments are at L1-l2 vertebrae; Lumbar segements are at T 11, T12 & L1 Embryo Adult C1 vertebra C1 C8 T1 vertebra T1 nerve L1 Fig. 4.48 Grants Atlas, 12th ed. L1 S1 S1 Posterior Longitudinal Ligament •Located Posterior to the vertebral bodies •Located Anterior to the spinal cord •Resists Flexion of the spine (bending forward) Herneated disks in the cervical region follow the same rule, but for a different reason. ---One exception--- Herniated Nucleus Pulposus Clinical Rule: A protruded nucleus pulposus, when small, will usually affect the spinal nerve whose number corresponds to the number of the vertebra below the disk. Other forms of encroachment on nerve roots 1. Arthritic enlargement of facet joints 2. Bony projections from traumatic or arthritic reactions with the interbody joints (of Luschka) which then encroach upon anterior parts of the cervical foramina. 3. Fractures or dislocations at any vertebral level Today’s Dissection • Even numbered tables: Deep Back, and once-over on Suboccipital Region • Odd numbered tables: Laminectomy and spinal cord T6- L5 – Clear out deep back muscles bilaterally – Saw through laminae; angle saw to enter spinal canal, with as wide an opening as possible – Observe structures inside the vertebral canal: meninges, nerve rootlets, etc.