Peripheral nervous system, origin

Marchevsky AM. Mediastinal tumors of peripheral nervous system origin. Semin Diagn Pathol. 1999 16 65-78. 

DAT is predominantly expressed by dopaminergic brain neurons, NET by noradrenergic neurons in the central and peripheral nervous system, and SERT is restricted to the axons of serotonergic neurons, which originate in the raphe nuclei and innervate numerous higher brain regions therefore SERT is widely distributed in the brain. Outside the brain, 5HT transport can be measured on non-neuronal cells (e.g. platelets, lympho-blastoid cells and smooth muscle cells) most of the 5HT appearing in the circulation is taken up by platelets. 

Neuropathic pain is defined as spontaneous pain and hypersensitivity to pain associated with damage to or pathologic changes in the peripheral nervous system as in painful diabetic peripheral neuropathy (DPN), acquired immunodeficiency syndrome (AIDS), polyneuropathy, post-herpetic neuralgia (PHN) or pain originating in the central nervous system (CNS), that which occurs with spinal cord injury, multiple sclerosis, and stroke. Functional pain, a relatively newer concept, is pain sensitivity due to an abnormal processing or function of the central nervous system in response to normal stimuli. Several conditions considered to have this abnormal sensitivity or hyperresponsiveness include fibromyalgia and irritable bowel syndrome. 

The central nervous system arises from a thickened area of the ectoderm called the neural plate on day 19 in the human embryo. This process is referred to as induction. The neural plate then differentiates into the neural tube (providing the origins for the brain and spinal cord) and the neural crest (forming the basis of the peripheral nervous system). The process by which the neural tube arises from the neural plate is referred to as neurulation. To form the neural tube, the neural plate changes shape and forms a pronounced groove, closing from the cranial end to the caudal end. The neural tube has openings on both ends that close on about day 25 and day 27, respectively. 

Local application of concentrated sodium channel blockers can provide complete pain relief through nerve conduction block (local anesthetics). This approach to pain relief is limited to a few applications involving short-term treatment of acute pain, since sodium channels are also vital to conduction in the heart, CNS, skeletal muscle, and non-nociceptive sensory neurons. However, some types of chronic pain signaling appear to be sensitive to sodium channel blockers at concentrations that do not cause conduction block. In particular, neuropathic pain, defined as chronic pain resulting from a primary lesion or dysfunction of the peripheral nervous system by the International Association for the Study of Pain (IASP) [58], is thought to originate from aberrant signaling in the nervous system and can be ameliorated by sodium channel blockers. 

The central effects are dependent on a first type of cannabinoid receptor (CBl), which is present in the brain. Furthermore, Munro et al. [Nature (1993) 365, 61-65] have cloned a second cannabinoid receptor coupled to protein G, called CB2, which is present only in the peripheral nervous system and more particularly on the cells of immune origin. The presence of CB2 cannabinoid receptors on the lymphoid cells may... 

A central nervous system (CNS) can be easily distinguished from a peripheral nervous system (PNS), since it contains most of the motor and the nucleated parts of neurons that innervate muscles and other effectors. The PNS contains all the sensory nerve cell bodies with some exceptions, plus local plexuses, local ganglia, and peripheral axons that make up the nerves. Most sensory axons go all the way into the central nervous system while the remaining relay in peripheral plexuses. Motor axons originating in the CNS innervate effector cells. 

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