الاربعاء Lec.10 أ. د. عبد الجبار الحبيطي

 Is the second part of C.N.S which occupies the vertebral canal of the vertebral column. It starts as the continuity of lower end of medulla oblongata. at the level of foramen magnum and terminates inferiorly as tapered part known as conus medullaris at the lower border of L1 vertebra (in adult) while in new born babies ends at the upper border of L3 vertebra. The spinal cord is nearly cylindrical in shape which shows 2 fusiform enlargement; a cervical enlargement (gives the brachial plexus) its maximum diameter at the 6 th cervical vertebra, & a lumbar enlargement (for lumbo-sacral plexus) whose maximum diameter at 12 th thoracic vertebra.

 The average length of spinal cord is 45 cm, from the apex of conus medullaris a prolongation of spinal cord pia matter extends to be attached to the back of the coccyx and called as filum terminale.  From the sides of the spinal cord 31 pairs of spinal nerves are attached: - 8 cervical, 12 thoracic, 5 lumbar, 5 sacral & 1 coccygeal. Each nerve is attached to the side of spinal cord by 2 roots, the segment of the cord to which the 2 roots attached is called a spinal segment.

 Due to the fact that the spinal cord being shorter than the vertebral canal, the roots of the nerves show progressive obliquity from above down wards, & the spinal segments do not lie opposite the corresponding vertebrae. Thus the levels of the spinal nerves are as follows: - In the cervical region add 1 to the number of vertebra e.g. the 5 th cervical vertebral spine, lies opposite the 6 th cervical segment of the spinal cord. In the upper half of thoracic region add 2 to the number of the thoracic vertebral spine. In the lower thoracic & upper lumbar region add 3 to the number of the vertebra. The lower lumbar & sacral region (conus medullaris) lie opposite the 12 th thoracic & first lumbar vertebrae.

 The spinal cord is surrounded by 3 layers of meninges as that for the brain, the outer dura, middle arachnoid & inner pia matter in direct contact and adheres to the spinal cord.  The pia of spinal cord gives: - I. Tooth lies processes horizontally runs transversely between the roots of spinal nerves & called ligamentum denticulatum. II. Filum terminale.

 The dura matter: - is the outer most & hardest coat, extends as the continuity of meningeal part of the brain dura matter (attaches to the circumference of foramen magnum, bodies of 2 nd -3 rd cervical vertebrae, back of coccyx & intervertebral foramina). The dural tube ends below at the level of the 2 nd sacral vertebra where it forms a sheath around the filum terminale from below the conus medullaris to the 2 nd sacral vertebrae Known as dural sac (terminal ventricle or 5 th ventricle). This dural sac contains: - I. Filum terminale. II. Nerve roots from below L1 till last spinal nerve roots (i.e. L2- coccygeal 1). Both I & II considered together as the cauda equine. III. C.S.F. which represent a mixture of C.S.F coming from the ventricles of the brain with that of the subarachnoid spaces.

 Cauda equine: - Is formed by the roots of the lumbar, sacral & coccygeal nerves which descend obliquely around the filum terminale to reach the various level of the corresponding intervertebral foramina. The cauda equine lies in the subarachnoid space below the end of the spinal cord.

I. Two posterior spinal arteries, one arises from each vertebral arteries. Each posterior spinal artery divided into 2 branches; which descends around the posterior roots of the spinal nerves on each side. II. A single anterior spinal artery forms by a contribution from both vertebral arteries, it descends on the anterior median fissure of the spinal cord. III. Radicular arteries arising from the local arteries in the region & enter the vertebral canal through the intervertebral foraminae. IV. Arteria magna radicularis arises from an intersegmental branch of the aorta.

Drains by 6 longitudinal venous channels which run along the whole length of spinal cord: - I. One runs in the median plane anteriorly. II. One runs in the median plane posteriorly. III. A pair runs vertically close to the ventral roots of spinal nerves. IV. A pair runs vertically close to the dorsal roots of spinal nerves.

All these venous channels communicate with: - I. The internal vertebral venous plexus. II. Veins of the medulla oblongata.

 Is the process for getting C.S.F. sample from the dural sac by a needle introduced between L3-L4 or L4-L5. The needle should pass through the following structures: - I. Skin. II. Subcutaneous C.T. III. Supraspinous ligament. IV. Interspinous ligament. V. Ligamentum flavum. VI. Loose areolar tissue containing the internal vertebral venous plexus in the epidural (extradural) space of the vertebral canal. VII. Dura matter.

I. Lumbar puncture to obtain a sample. II. Caudal anesthesia inserts into the sacral canal through the sacral hiatus to obtain block for the spinal nerve root during the second stage of labor. III. Injection of some drugs for the treatment of some diseases as in meningitis. IV. Injection of a dye to get myelogram of the spinal cord.