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Spinal cord diseases

The spinal cord diseases are one of the most common kinds of problems faced by the humans. The spinal cord which lies within the vertebral column begins from the foramen magnum where it is continuous with the medulla oblongata and extends down to the level of first or second lumbar vertebrae. At its lower end the cord terminates to form conus medullaris from whose end a delicate filament called filum terminale extend to the coccyx.

During embryonic development, the growth of the cord lags behind that of the vertebral column so the cord ends higher up and the spinal nerves take an oblique downward course to exit. The result is that the spinal segments do not correspond with the vertebrae. Cord consists of eight cervical, twelve dorsal, five lumbar, four sacral and one coccygeal segment.

The upper cervical cord segments lie behind the same numbered vertebral body whereas lower cervical segments are located one above each corresponding vertebrae (Add 1 ie the portion of spinal cord behind C 5 vertebra is C6 segment). For upper thoracic cord two segments higher (For thoracic vertebrae 1-6 add 2) for lower thoracic cord three segments higher (For thoracic vertebra 7-9 add 3). The lumbar and sacral cord segments lie behind the 10th thoracic to first lumbar vertebrae.

Spinal cord diseases

The spinal cord like brain is surrounded by three meninges. Pia is a fibrous membrane forming immediate cowering of the cord while arachnoid is a transparent membrane lying superficial to pia separated by sub arachnoid space in which cerebrospinal fluid lies. Duramater which lines the vertebral canal extends to the second or third sacral vertebrae.

Spinal cord is made up of central grey and peripheral white matter which is made up of ascending and descending fibers of spinal tracts. It is divided into three columns – anterior column, lateral column and posterior column while anterior homs of grey matter contain ganglion cells, the axons of which comprises the anterior roots and constitute lower motor neurons.

The portion of the muscles and skin supplied by each spinal segment is called myotomes and dermatomes respectively and it is important to determine the level of involvement of spinal cord by referring to these levels.

Thus the functions of the motor and sensory tracts to a large extent are interrupted by the lesion and by examination of these functions it is possible to determine the level below which muscular weakness occurs and sensory functions are impaired.

Lower motor neuron is formed by the anterior horn cell and its axons. This acts as final common pathway for the transmission of motor impulses to the muscles and when the segmental arc is involved, tendon reflexes are lost.

Upper motor neuron is formed by long descending fibres ending in anterior horn cells and the neurons supplying different groups of muscles are arranged in the anterior horn in a definite manner. Upper motor neuron lesion produces spastic paralysis with tendon reflexes exaggerated or brisk.

Spinal cord has a rich blood supply consisting of two posterior and one anterior spinal artery. These are reinforced at all levels by segmental arteries. Spinal cord is involved by a number of diseases ranging from congenital anomalies, compressive lesions, inflammatory and demyelinating disorders.

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