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Organisation Of The Spinal Cord Notes

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Spinal Cord level of cord termination in adult and newborn
-The spinal cord is continuous with the medulla, and runs down to the level of L1/L2 in the adult and L3/L4 in the newborn due to the faster growth of the vertebral column compared to the cord itself.
-Lumbar puncture: Intrathecal injectin into CSF: Spinal anaesthesia, can be used to decrease intracranial pressure. Patient in foetal position- aim between L4/5. The cadua equine nerve rootlets float away from the needle NB: approximately 30% of the population have a spinal cord that ends lower and a small proportion have one that ends very low and could be damaged by a lumbar puncture.
-Subarachnoid space ends at S2, cauda equina, consequences of compression of cauda equina Extension: Cauda Equina syndrome
-The sub-arachnoid space ends at the level S2.
-The spinal cord narrows caudally as the conus medullaris.
-In the region between the end of the spinal cord and the end of this space there are spinal nerves, forming the cauda equina.
-Cauda Equina syndrome can be caused by anything that interferes with the functioning of the cauda equina.The most common cause is herniation of the nucleus pulposus in lower lumbar regions directly backwards; another is metastasis.
-In the most severe cases, much of the cauda equina is compressed, leading to a wide range of symptoms including paraplegia, sciatica, weakness of urinary and faecal sphincters, saddle anaesthesia. These are due to compression of nerve roots from L1 to S5, which make up the cauda equina. This condition is a medical emergency and usually requires surgery. Core: filum terminale
-There is also a strand of connective tissue called the filum terminale, which joins the end of the cord (the conus medullaris) to the dorsal surface of the first vertebra of the coccyx. Spinal cord organisation Core: lumbar and cervical enlargements
-The spinal cord has a cylindrical shape but there is a cervical enlargement at C3-T1, (max circumference at C6) where the spinal nerves form the brachial plexus and a lumbar enlargement at L1-S3 (max circumference at L3) in the region of the lumbo-sacral plexus.

-The amount of white matter is greatest rostrally: ascending tracts increase in size as one moves up the cord-sensory fibres are added to the cord from caudal to rostral; descending tracts decrease in size as one moves down the cord-descending tracts diminish from rostral to caudal as axons terminate
-In the cervical segments, the ventral horn is larger to accommodate the increased number of motor neurons; the dorsal horns are also larger at upper certical segments - increased sensory innervations to hand. The white matter is also increased (large gracilis and cuneatus dorsal columns and large lateral and anterior columns)
-In the thoracic segments, there is less grey matter but prominent lateral horns as there are pre-ganglionic nerve cells to the sympathetic chain but also Clarke's columns which sends proprioceptive fibres from muscle spindles and Golgi tendon organs to the cerebellum); the cuneate fascilulus (lateral of the dorsal colums) is reduced as fibres from the upper limb have not yet entered the tract)
-In the lumbar segments, there are large amounts of grey matter (innervations of lower limb) - the dorsal horns are at their largest because most sensory information is concerned with reflexes to keep us upright; the ventral horn has the largest motor neurons with long axons to leg/foot. Of the white matter, only the gracile fasciculus exists.
-The lower sacral section has a high proportion of grey matter relative to its white matter but the overall dimensions of the cord at this level are small, making the total grey matter content low.

Meninges of the spinal

cord

Core: arachnoid space, pia

dura, arachnoid, subExtension:

denticulate ligaments, subarachnoid

septum

-

Like the brain,

the spinal cord is covered by meninges.
-The pia mater is a thin, vascular membrane apposed to the cord itself.

-

dorsal and ventral processes pierce the dura providing support for the

closely
-The denticulate ligament is a continuation of the pia a narrow sheet of fibrous tissue on either side of the spinal cord with 21 tooth-like processes lying between the roots - these denticulate arachnoid and attach to the spinal cord.

-The arachnoid mater covers the pia and encloses the sub-arachnoid space, which is filled with CSF.
-On the posterior surface, the arachnoid mater is linked to the pia in the midline by a non-continuous sheet of fibrous tissue called the subarachnoid septum.
-The dura mater is the outermost covering of the cord, separated from the arachnoid by the sub-dural space, a potential space containing a thin film of serous fluid.
-Unlike in the brain, the dura is not fused with the periosteum of the surrounding bone, but is separated from it by the epidural space, which is filled with semi-liquid fat and an extensive venous plexus and the small arteries supplying the vertebral canal contents.
-Anaesthetics can be inserted into this space and will act on whole spinal segments.
-The dura is, however, attached to the periosteum at the circumference of the foramen magnum, to the posterior surfaces of the bodies of C2 and C3 vertebrae and through fibrous attachments to the posterior longitudinal ligaments of the vertebrae especially at the lower end of the vertebral canal.

Blood supply Core: vessels: anterior and postero-lateral spinal arteries; reinforcements (artery of Adamkeweitz) Extension: radicular arteries and veins
-The vertebral artery gives off branches supplying the spinal cord as well as branches supplying the brain: the anterior spinal artery and the paired posterior spinal arteries.
-The anterior spinal artery runs in the pia mater of the anterior median fissure.
-The posterior spinal arteries run next to the emerging dorsal nerve rootlets, close to the posterolateral sulcus. Although these vessels carry blood cranio-caudally along the entire length of the spinal cord, it is only the cervical region that receives a sufficient supply.
-Anastomoses with radicular arteries that branch from segmental arteries such as the ascending cervical, intercostal and lumbar arteries, fulfil the requirements of more caudal regions of the cord.
-There are particularly large radicular arteries at the cervico-thoracic junction and at the thoraco-lumbar junction.
-At the thoraco-lumbar junction is the artery of Adamkiewicz (or great radicular artery)-Large reinforcing vessel at the thoraco-lumbar junction important for the supply of the lumbo-sacral part of the cord. It is at risk when abdominal aortic aneruysms have to be repaired

-This is a branch of the descending aorta and can spare the legs from paralysis with its supply to caudal segments if there is thrombosis in the anterior spinal artery.
-When this is damaged or obstructed, it can result in anterior spinal artery syndrome, with loss of urinary and fecal continence and impaired motor function of the legs.
-The venous drainage runs closely with the arterial supply: there is a single posterior spinal vein (behind the posterior median sulcus and septum), a pair of posterolateral spinal veins (behind the dorsal nerve roots), a single anterior spinal vein (in front of the anterior median fissure) and a pair of anterolateral spinal veins (behind the ventral nerve rootlets).
-These drain via radicular veins to the internal vertebral venous plexus in the epidural space. This plexus is continuous with the dural venous sinuses in the skull via the foramen magnum.

Spinal nerve exit foramina and intervertebral discs Core: dorsal and ventral roots, dorsal root ganglia, anatomy and MRI appearance of intervertebral exit space; consequences of compression of the spinal nerves

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