Spinal nerves dorsal root

The neuropathological analysis of HIV-associated neuropathies should include the different central and peripheral nervous system structures associated with sensory pathways, including spinal cord, dorsal root ganglia (DRG), peripheral nerve, and cutaneous nerve fibers (Pardo et al. 2001) (Fig. 4.1). The majority of studies have focused on the evaluation of the peripheral nerve, often from sural nerve biopsies and the DRG. Few studies have examined the pathology of sensory pathways in the... 

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.

Stretching of the muscle is sensed in the muscle spindle and leads to firing in muscle spindle afferent. These nerves travel via the dorsal root and synapse in the anterior horn of the spinal cord directly with the motor neurone to that muscle. They stimulate firing of the motor neurones, which causes contraction of the muscle that has just been stretched. The muscle spindle afferent also synapses with inhibitory interneurons, which inhibit the antagonistic muscles. This is called reciprocal innervation. 

It contracts in response to an impulse of its motor nerve. In executing motor programs, the brain sends impulses to the spinal cord. These converge on a-moto-neurons in the anterior horn of the spinal medulla. Efferent axons course, bundled in motor nerves, to skeletal muscles. Simple reflex contractions to sensory stimuli, conveyed via the dorsal roots to the motoneurons, occur without participation of the brain. Neural circuits that propagate afferent impulses into the spinal cord contain inhibitory interneurons. These serve to prevent a possible overexcitation of motoneurons (or excessive muscle contractions) due to the constant barrage of sensory stimuli. 

Forms of local anesthesia. Local anesthetics are applied via different routes, including infiltration of the tissue (infiltration anesthesia] or injection next to the nerve branch carrying fibers from the region to be anesthetized (conduction anesthesia of the nerve, spinal anesthesia of segmental dorsal roots), or by application to the surface of the skin or mucosa (surface anesthesia]. In each case, the local anesthetic drug is required to diffuse to the nerves concerned from a depot placed in the tissue or on the skin. 

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). 

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).

Hu, P., and McLachlan, E. M. (2003). Distinct functional types of macrophage in dorsal root ganglia and spinal nerves proximal to sciatic and spinal nerve transections in the rat. Exp. Neurol. 184,... 

Jin, S. X., Zhuang, Z. Y., Woolf, C. J., andji, R. R. (2003). p38 mitogen-activated protein kinase is activated after a spinal nerve ligation in spinal cord microglia and dorsal root ganglion neurons and contributes to the generation of neuropathic pain. J. Neurosci. 23, 4017—4022. 

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-... 

Michael GJ, AveriU S, Nitkunan A, Rattray M, Bennett DL, Yan Q, Priestley JV (1997) Nerve growth factor treatment increases brain-derived neurotrophic factor selectively in TrkA-expressing dorsal root gangUon ceUs and in their central terminations within the spinal cord. J... 

Zhou XF, Deng YS, Xian CJ, Zhong JH (2000) Neurotrophins from dorsal root ganglia trigger allodynia after spinal nerve injury in rats. Eur J Neurosci 12 100-105... 

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. 

Actually, unipolar neurons have two axons rather than an axon and dendrite (Figure 14.3). Mostintemeurons, which form all the neural wiring within the CNS, are of this type. Examples include spinal ganglia, most cranial nerve sensory ganglia, and the trigeminal mesencephalic nucleus. Dorsal root ganglia cells extend one axon centrally toward the spinal cord, and the other axon toward the skin or muscle. 

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