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Spinal Cord and Meninges

- See: Neuro Exam:

- Discussion:
    - vertebral canal houses the spinal cord and its meningeal coverings;
    - medulla oblongata is continuous w/ spinal cord at foramen magnum, &spinal cord usually ends inferiorly at level of 1st or 2nd 
          lumbar vertebra;
    - filum terminale:
          - at tapered inferior end of spinal cord, cord of filum terminale, continues inferiorly to merge w/ periosteum on dorsum of coccyx;
    - spinal dura:
          - separated from inner surface of bones forming vertebral canal by epidural space containing fat and a rich plexus of veins;
          - dural sac continues inferiorly to middle of second sacral vertebra;
          - pia mater is closely attached to spinal cord, & subarachnoid space, containing cerebrospinal fluid, is space between it & arachnoid
                  which lies on inner surface of dura;
    - spinal nerves:
           - leave vertebral canal through intervertebral foramina;
           - each nerve is formed by union of a dorsal root and a ventral root, usually at intervertebral foramen;
           - subarachnoid space is prolonged in a duralarachnoid sheath around each dorsal and ventral root, roughly to the level of union of roots;
           - since cord is shorter than vertebral column, nerves slope inferiorly from their origin to appropriate intervertebral foramina;
           - below inferior end of cord, duralarachnoid sac contains a leash of nerve roots and the filum terminale;
           - this complex constitutes the cauda equina;
    - cervical spinal nerves:
           - there are eight pairs of cervical nerves & seven cervical vertebrae, hence cervical nerves are numbered according to vertebra
                  above which they emerge;
           - 5th cervical nerve emerging above 5th vertebra;
           - 8th cervical nerve emerges between C7 & T1;
    - thoracic cord & spinal nerves:
           - since thoracic nerves are numbered according to the vertebra below which they emerge, protrusion of the disc between the 5th and 
                  6th thoracic vertebrae would compress the roots of the 5th thoracic nerve;
    - lumbar spinal nerves:
           - intervertebral foramina in lumbar region are larger than lumbar nerves;
           - each nerve emerges thru upper part of foramen and lies against body of vertebra above;
           - protrusion of lumbar disc will not affect nerve corresponding in number to that intervertebral discs (that nerve emerges above 
                  the disc);
           - protruded disc usually compresses next lower nerve as that nerve crosses level of disc in its path to its foramen;
                  - hence, protrusion of fifth lumbar disc usually affects S1 instead of L5;
    - myelomere:
           - because spinal cord is shorter than vertebral column, level of emergence of spinal nerve is below level of segment of spinal cord 
                  from which it arises;
           - myelomere, or segment of cord from which nerve root arises, lies one level above the same numbered vertebral body;
           - between C2 and T10 , number of cord segment is the number of spinous process, plus two;
                  - T5 myelomere lies at the level of the T4 vertebral body;
                  - T6 overlies T8 thoracic segment of  spinal cord;
                  - lumbar and sacral myelomeres are concentrated between T11 and L1 vertebral bodies;
                          - spinous processes of T11 & T12 overlie 5 lumbar segments;
                  - conus medullaris is usually found at level of L1-L2 intervertebral disc & contains myelomeres of the 5 sacral nerve roots;
                  - L1 spinous process overlies five sacral segments of the spinal cord;
    - cord injuries:
           - neurologic injury above the T-10 are related purely to cord damage;
           - injuries occuring between T-10 and L1 have mixed injury patterns;
           - injuries occuring below L1, cause purely peripheral nerve root damage


   Organization of intrathecal nerve roots at the level of the conus medullaris.

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