View from above onto L4 during spinal anesthesia. Simplified representation, the proportions do not match reality.
Spinal anesthesia is a form of regional anesthesia where anesthetic is injected in selected segments of the caudal portion of the spinal cord. Methodically it is a central nerve block.
In spinal anesthesia the needle penetrates the dura mater, as opposed to the procedure in epidural anesthesia, and penetrates into the space containing the cerebrospinal fluid. The local anesthetic, usually bupivacaine, can spread freely in the cerebrospinal fluid and anesthetize the spinal cord and corresponding nerve fibers in the spinal canal.
Source: Anka Friedrich via wikipedia
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