May 15, 2012

Spina bifida

Spina bifida, which literally means "cleft spine," is a term used to describe the incomplete development of the brain, spinal cord, and/or meninges (the protective covering around the brain and spinal cord).

The human nervous system develops during the first month of pregnancy. It begins as a small plate of specialized cells along the embryo's back. As the edges of this sheet begin to curl toward each other, they form the neural tube -- a slender sheath that closes to form the embryo's brain (the top of the tube) and spinal cord (the rest of the tube). This development is generally finished by the fourth week of pregnancy. If any problems arise during this process, the consequence may be a set of disorders known as neural tube defects. One of these defects is spina bifida, the most common kind of neural tube defect. With spina bifida, the tissues that fold to form the neural tube do not close or do not stay entirely closed. This leaves an opening in the vertebrae -- the small bones that form the backbone and encircle and protect the nerves of the spinal cord. This defect happens just a few weeks (21 to 28 days) after conception, typically before a woman even knows that she is pregnant.

How much spinal column stays open influences the extent of nerve damage. The defect may result in loss of sensation and major muscle weakness in the lower portion of the body. The degree of paralysis depends on which section of the spinal cord is involved. The higher the defect is found on the body, the more extensive the paralysis. The condition also may be linked with a large buildup of pressure in the brain. Caused by an accumulation of spinal fluid, this situation may result in mental retardation unless it is surgically remedied.

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