Sciatic Nerve
There are 31 pairs of spinal nerves which branch off from the spinal cord. In the cervical region of the spinal cord, the spinal nerves exit above the vertebrae. A change occurs with the C7 vertebra however, where the C8 spinal nerve exits the vertebra below the C7 vertebra. Both the nerves and the segments in the spinal cord are numbered in a similar way to the vertebrae. The point at which the spinal cord ends is called the conus medullaris, and is the terminal end of the spinal cord. It occurs near lumbar nerves L1 and L2. The peripheral nervous system refers to parts of the nervous system outside the brain and spinal cord. It includes the cranial nerves, spinal nerves and their roots and branches, peripheral nerves, and neuromuscular junctions. The anterior horn cells, although technically part of the central nervous system (CNS), are sometimes discussed with the peripheral nervous system because they are part of the motor unit. Branches of the cervical and lumbosacral spinal nerves anastomose peripherally into plexuses, then branch into nerve trunks that terminate up to 1 μm away in peripheral structures. The intercostal nerves are segmental. The term peripheral nerve refers to the part of a spinal nerve distal to the nerve roots. The sciatic nerve is the longest and largest nerve in the body; it measures three-quarters of an inch in diameter. It originates in the sacral plexus; a network of nerves in the low back (lumbosacral spine). The lumbosacral spine refers to the lumbar spine and the sacrum combined. The sciatic nerve starts in your low back, which is called your lumbar spine. The nerve roots are at the L4 and L5 vertebrae (the 'L' means lumbar, and the numbers indicate the level of the vertebra—where it is in your back). The sciatic nerve also travels through your pelvic region (sacrum). Any of the nerves that arise in pairs from the spinal cord. The spinal nerves are distinguished from the cranial nerves, which, apart from the vagus nerve, are limited in their distribution to the head and neck. Like the cranial nerves, the spinal nerves are part of the peripheral nervous system. There are 31 pairs of spinal nerves in the human body: 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 1 coccygeal. These emerge through spaces between the vertebrae. It consists solely of motor nerve fibers. The posterior root springs from the posterior part of the spinal cord, and consists of fibers which lead to the posterior column of the cord. These fibers are all sensory fibers. On the posterior there is a small bulg Nerves are pretty small. Consider that the human spinal cord, with its many, many nerve pathways, is under 10 mm in diameter at it widest point. Individual nerves have diameters ranging from perhaps 4 to 100 micrometers, depending on the location The roots of the spinal nerves are also shown. (B) Microscopic view of the spinal cord in cross-section (x5). There are 31 pairs of spinal nerves, each pair numbered according to the level of the spinal cord from which it arises (see Fig. 5-11) . Each nerve is attached to the spinal cord by two roots: the dorsal root and the ventral root (see Fig. 5-12) . On each dorsal root is a marked swelling of gray matter called the dorsal root ganglion, which contains the cell bodies of the sensory neurons. Each spinal nerve continues only a short distance away from the spinal cord and then branches into small posterior divisions and larger anterior divisions. The larger anterior branches interlace to form networks called plexuses, which then distribute branches to all parts of the body (see Fig. The sciatic nerve is a large nerve that originates from the distal spinal cord and extends along nearly the entire length of the hind limb. In most vertebrates, it's the major branch of the sacral plexus, a complex mass comprised of neurons that exit the spinal column via spinal nerves L4 through S4.  Behind your knee, smaller nerves branch out from the sciatic nerve and travel down to your feet. 1  Your sciatic nerve is part of a complex structure: your body's nervous system. 2  That system is responsible for transmitting pain and sensation to other parts of your body. The sciatic nerve starts in your low back, which is called your lumbar spine. The nerve roots are at the L4 and L5 vertebrae (the 'L' means lumbar, and the numbers indicate the level of the vertebra—where it is in your back). The sciatic nerve also travels through your pelvic region (sacrum).
http://cnsvp.stanford.edu/atlas/spinal_cord1/ http://emedicine.medscape.com/article/1948687-overview http://www.spineuniverse.com/conditions/sciatica http://www.daviddarling.info/encyclopedia/S/spinal_nerve.html http://www.answers.com/Q/What_is_the_diameter_of_a_nerve http://encyclopedia.lubopitko-bg.com/The_Spinal_Nerves.html http://www.unm.edu/~toolson/sciatic_nerve.html http://www.spineuniverse.com/conditions/sciatica
which branch of a spinal nerve is the widest in diameter