Spinal nerves ventral root

Figure 7.1 Cross-sectional view of the spinal cord. In contrast to the brain, the gray matter of the spinal cord is located internally, surrounded by the white matter. The gray matter consists of nerve cell bodies and unmyelinated intemeuron fibers. This component of the spinal cord is divided into three regions the dorsal, lateral, and ventral horns. The white matter consists of bundles of myelinated axons of neurons, or tracts. Each segment of the spinal cord gives rise to a pair of spinal nerves containing afferent and efferent neurons. Afferent neurons enter the spinal cord through the dorsal root and efferent neurons exit it through the ventral root.

The cell bodies of somatic motor neurons are found in the ventral horn. The axons of these neurons exit the CNS through the ventral root of the spinal nerve and innervate skeletal muscles. The two types of motor neurons located in the ventral horn are ... 

The spinal cord is the major route of input and output for the centrai nervous system. It is covered by the meninges and sits within the vertebral column. There are 31 pairs of spinai nerves, exiting at the dorsal and ventral roots of the spinal cord. The spinal cord is divided into four levels (superior to inferior) cervical, thoracic, lumbar, and sacral. A cross section of the spinal cord shows a butterflyshaped core of gray matter (neuronal soma), and an outer surrounding area of white matter (axon tracts). 

Dissect the vertebral column. Note the cell bodies of lumbar motor neurons are more rostral than their exit points, i.e., L4 cells bodies are in upper lumbar or even lower thoracic vertebrae, even though the spinal nerve exits at the fourth lumbar vertebrae. The more caudal vertebral column contains only the cauda equina, the dorsal, and ventral roots of lower lumbar and sacral motor neurons (Fig. 20.2). 

Grasping each spinal nerve, follow it to its bifurcation into the ventral (motor) and dorsal (sensory) roots (see Note 2). 

Cut the ventral root free at the bifurcation point and as close to the spinal cord as possible (NB ventral roots enter cord proximal to spinal nerve entry point). 

Fig. 20.3. Dorsal and ventral root dissection. The anatomy of the ventral and dorsal roots during dissection is shown. Mouse is prone (rostral is up) and the left sciatic nerve (Sci) has been exposed along the femur and to its origin at the lumbar spinal nerves. The spinal nerves are labeled (lumbar 3 through 6). The ischium (Isch) has been removed to follow the sciatic nerve. The inset shows the L4 root separated into its ventral and dorsal roots, note the DRG associated with the dorsal root. The scale bar is 6 mm. (Color figure is available online).

The PNS is defined as that part of the nervous system external to the brain and spinal cord (Figure 30.1). As such, the PNS includes the cranial nerves, dorsal and ventral spinal roots, spinal nerves and their branches, and ganglia. The primary function of the PNS is to convey sensory and motor information, including informa-... 

At cross section, the gray matter is the cord from the anterior and posterior columns, which contains the motoneurons and sensory neurons, respectively. An important feature of each spinal cord segment is the presence of a pair of roots (or associated branches or rootlets) called the dorsal and ventral roots. The dorsal roots contain sensory axons whereas the ventral roots contain motor axons. These sensory and motor axons, which are part of the peripheral nervous system, become mixed in the spinal nerves en route to their peripheral targets. The spinal nerves, which are also components of the peripheral nervous system, transmit sensory information to the spinal cord and motor commands to the muscles and viscera. 

At peripheral nerves the reduction in sodium influx leads to a decrement in action potential formation and propagation. In animal studies a reduction in action potential by 50% is necessary for observable loss of neuronal function and exposure length of the nerve fiber is important in conduction blockade [41]. At central neuraxial administration of LA similar mechanisms to those previously discussed occur at the level of the spinal nerve roots. Additionally, at the dorsal horn, LA possibly exert action at sodium and potassium chaimels in ventral and dorsal horn neurons [41]. Furthermore local anesthetics may exert action at neurotransmitters or neuropeptides such as substance P or y-aminobutyric acid (GABA) by either directly binding to receptors or by altering local pharmacokinetics of endogenous agonists [41 ]. 

Epidural fentanyl has been used in practice since 1975. When fentanyl is placed in the epidural space, it must first cross the dura mater before it can reach the spinal cord. Epidural fentanyl binds to opioid receptors located throughout the spinal cord and nerve roots, and provides analgesia. The epidiu-al space is highly vascularized, and some redistribution of drug to the systemic circulation occiu. The epidiu-al space also contains fat, connective tissues, a lymphatic network, and the dorsal and ventral roots of the spinal nerves, all of which can serve as repositories for hpophilic agents. 

By the spinal accessory nerve which is formed by the spinal roots (upper 5 cervical ventral roots) they ascend through the foremen magnus, to exit through the jugular foremen, after joining the cranial roots. 

FIGURE 1-2 TransversesectionofarabbitlumbarspinalcordatL-1. Gray matter is seen as a paler-staining area in an H configuration formed by the dorsal and ventral horns with the central canal in the center ( ). The dorsal horns would meet the incoming dorsal spine nerve roots at the upper arrows. The anterior roots can be seen below (lower arrows), opposite the ventral horns, from which they received their fibers. The white matter occupies a major part of the spinal cord and stains darker. Epon section, 1 pm, stained with toluidine blue. 

The cells that give rise to the preganglionic fibers of this division lie mainly in the intermediolat-eral columns of the spinal cord and extend from the first thoracic to the second or third lumbar segment. The axons from these cells are carried in the anterior (ventral) nerve roots and synapse with neurons lying in sympathetic ganglia outside the cerebrospinal axis. Sympathetic ganglia are found in three locations paravertebral, prevertebral, and terminal. 

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