[skin and the Autonomic Nervous System].

In acute noxious injuries to the spine, usually the somatic sensory and motor dysfunctions originate an acute pain which is referred to as acute “nociceptive” or somatic pain (Figure 1). In occasional situations the pain may have a tendency to persist for months or several years after the original injury has healed. This type of persistent pain has been referred to as “neuropathic pain.” Descriptors. autonomic nervous system, complex regional pain syndrome(CRPS), neuropathic pain, parasympathetic nervous system, somatic nervous system, sympathetic nervous system INTRODUCTION The autonomic and somatic nervous systems are the integral anatomical and physiological components of the spine. The noxious (painful)stimuli are divided into somesthetic or somatic pain (no neurovascular component) and “neuropathic” pain (associated with neurovascular changes) due to the fact that the majority of the central and peripheral nervous system dysfunctions are somatic in nature, the role of autonomic nervous system in neuropathic type of pain has been over-shadowed and ignored (Table I). The chronic, neuropathic pain-e.g., nerve root contusion, neuralgia, stump neuroma pain, and sympathetically maintained pain (SMP)becomes persistent and has a tendency to affect the function of the sympathetic nervous system (SNS). The neuropathic pain has a tendency to cause referred pain, spasm, chronic tissue damage, and inflammation. It may be accompanied by vascular and trophic changes. These chronic autonomic dysfunctions and their relation to the spine will be discussed in this article. THE AUTONOMIC NERVOUS SYSTEM The autonomic nervous system (sympathetic and parasympathetic nervous system) is mainly responsible for: (i). Control of the vital signs (blood pressure, pulse, and respiration)(1,2). (ii). Control of body temperature by achieving a balanced and stable homeostasis of the internal environment (“Milieu interne”)(1,2). This is done through sophisticated modulation of the body temperature, cell membrane exchange, and rate of metabolism. (iii). Control of the immune system: Any internal or external distress may stimulate the sympathetic system to up-regulate the immune system and T-cell lymphocyte function. This process leads to “neuroinflammation”(2-8). There are two major autonomic spinal structures: (i). thoracolumbar autonomic system, and (ii). craniocervical autonomic system. These two divisions are under reciprocal and putative influence of the higher centers of the brain and brain stem on one extreme, and the peripheral neurovascular structure on the other. The neuronal structures in the autonomic nervous system are divided into supraspinal, preganglionic, and postganglionic neurons. The preand postganglionic fibers are mainly poorly myelinated small c fibres. The chain of ganglia transmits the impulses vertically and horizontally, contributing to spread of pain, spasm, neuroinflammation, and at times spread of the full-blown disease such as complex regional pain syndrome (CRPS) (1,2,7,9,10) (Figure. 2).