02. The spinal cord
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- Category: 2- Anatomy
- Published on 26 April 2011
- Written by Ben Brahim Mohammed
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The spinal cord [ 38 , 160 ] is well protected within the spinal canal [ 43 ] inside the spine. In adults, it measures approximately 42 cm for women and 45 cm for men [ 13 , 14 , 15 , 16 , 17 , 19 ]. And it is at the origin of all 31 pairs [ 14 ] of spinal nerves [ 38 , 125 ].
The spinal cord, like the brain, is surrounded by the meninges membranes [ 43 ]: the pia mater [ 38 , 85 ], the arachnoid mater [ 64 , 94 ] and the dura mater [ 43 , 69 , 94 ]. It's surrounded by the CSF (The Cerebral Spinal Fluid) [ 95 ], and has a rudimentary hole in the center (the central canal) [ 14 , 20 ].
1. External configuration:
Because of intrauterine faster growth of the spine, the nerve roots of the spinal nerves are offset relative to Intervertebral foramina they emerge from. That is why the spinal cord ends at the level of the second lumbar vertebra (L2) [ 21 , 22 , 23 , 24 , 25 ] although it gives nerves up to the fifth sacral vertebra and even the first coccyx vertebra. [ 26 , 27 , 28 , 29 , 30 ]. The Lumbar puncture, for collecting CSF, is usually done below the second lumbar vertebra, this prevents any injury to the spinal cord [ 2 , 31 , 32 , 33 ].
The Spinal cord follows the path of the spine, and draws two curvatures: A Cervical with a posterior concavity (lordosis) and a dorso-lumbar with anterior concavity (kyphosis) [ 34 .] It also has two enlargements : [ 32 , 35 , 36 , 37 , 38 ]: a cervical and a lumbar, this is due to the innervation of the upper and the lower limbs. The Spinal cord ends down with the medullary cone [ 50 ] that gives rise to the Cauda equina [ 91 ] (A cluster of lumbosacral nerve roots).
2. Internal configuration:
On a cross section [ 43 ], the spinal cord has a central region: the gray matter which contains the neurons cell bodies, and a peripheral part: The white matter, it consists of the axonal extensions ant their myelin sheath [ 104 , 113 , 124 , 125 ].
The gray matter has the the shape of a butterfly, with two anterior horns housing the motor neurons cell bodies and two posterior horns that receive sensory fibers. At the thoracolumbar level, there are also lateral horns, these hold the sympathetic fibers cell bodies [ 40 , 41 , 42 ].
The white matter is organized into three pairs of funiculi [ 36 , 43 , 44 , 45 ] (ventral, dorsal and lateral).
The spinal cord is marked by some grooves on its surface : the deepest is the anterior median fissure (the groove in the ventral side), The posterior median sulcus is the groove in the dorsal side,
The spinal cord has also two lateral grooves on each side, from which will emerge two pairs of nerve roots, a front root (for motor fibers) and the posterior root(for sensory fibers).
These two nerve roots unite to form a spinal nerve on each side.