Spinal nerve nerve roots result in typical patterns of neurologic defects (muscle weakness, abnormal sensation, changes in reflexes) that allow localization of the responsible lesion. There are several procedures used in sacral nerve stimulation for the treatment of various related disorders. Sciatica is generally caused by the compression of lumbar nerves L4, or L5 or sacral nerves S1, S2, or S3, or by compression of the sciatic nerve itself. Spinal nerve A spinal nerve is a mixed nerve, which carries motor, sensory, and autonomic signals between the spinal cord and the body. In the human body there are 31 pairs of spinal
Nerve net The anatomy and positioning of nerve nets can vary from organism to organism. Hydra, which are cnidarians, have a nerve net throughout their body. On the other hand, sea stars, which are echinoderms, have a nerve net in each arm, connected by a central radial nerve ring at the center. This is better suited to controlling more complex movements than a diffuse nerve net. The emergence of true nervous tissue occurred following divergence in the last common ancestor of Porifera (sponges) and Cnidaria and Ctenophora. The existence of nerve nets is best understood by studying the outgroup of Porifera and