Conversely in visceral pain there is often fall of BP and vomiting These manifestations occur reflexly (autonomic reflex). [N.B. Many visceral pains,

muscular spasm may also (unfortunately) cause ischemia of the muscles and further aggravation of muscular pain (and thus a vicious cycle). This lype of condition (e.g. lumbago) are benefitted by massage and physiotherapy (iii) Changes in the autonomic nervous system Somatic pain is accompanied usually, by signs of sympathetic overactivity, eg, rise of BP, tachycardia and pupillary dilatation. Conversely in visceral pain there is often fall of BP and vomiting These manifestations occur reflexly (autonomic reflex). [N.B. Many visceral pains, e.g. intestinal colic, renal colic, myocardial infarction, torsion of ovarian cyst, etc may be associated with vomiting. Thus, (i) Vomiting does not necessarily mean that the pain is of Gl origin, and (n) vomiting often indicates that the underlying pathology is in an advanced stage; eg. vomiting in an acute attack of myocardial infarction often means a grave prognosis). (iv) Reflex response A painful stimulus is usually associated with somatic reflexes also; example: pinprick in the sole of foot withdrawal of the foot. Table 10B1. 21 Types (Classification) of pain PAIN Somatic Visceral (somasthetic) (from viscera) Eg : angina pect oris/peptic ul cer/intestinal colic/renal colic etc. Superficial Deep. (from skin and (from muscles/ subcutaneous tis- bones/joints/fas sue) cia/periosteum) Eg : superficial Eg : Fracture/ cuts/bums etc slipped inter vertebral disc/ arfhritis/fibro sitis, rupture of muscle belly/etc Interrelationship between threshold of pain and its reaction. It is a common experience, that some people, eg, prize fighting sportsmen (particularly boxers), poor manual workers (and others generally considered as occupying the lower rungs of society but physically tough persons), can absorb great pain showing little reactions of pain. On the otherhand, highly sophisticated people, old unmarried women and cantenkorous old persons show excessive reaction to pain. Reaction to the pain also depends upon the environment. Serious injuries may be sustained in a battle field or during boxing match and yet severe pain many not be felt. Question is, what happens ? Is the threshold of pain altered ? Or, some other factors are responsible for this phenomenon ? With our present state of knowledge, a definite answer cannot be given. Previous idea was that the threshold of pain is same in all persons but due to some reasons (not exactly known), the reaction of pain differs from person to person. It will be seen later in this chapter, that ideas have changed; it is now known that within our nervous system, there exists a mechanism, which can inhibit the pain. It is possible (but not proved) that persons who can absorb heavy physical punishment without showing much reactions, have rather a better functioning pain inhibiting mechanism. As an example, the story of a prize fighting boxer, the exworld champion, Muhammed Ah, may be cited. During a title fight, in the 3rd round, he sustained an injury which caused fracture of his jaw. Inspite of this, he continued till the 12th round (and thus received the jabbing, sometimes on the injured region, of a world class boxer). Neurotransmitter and path of pain 1. The transmitter The A (carrying ' first' pain) and the C (carrying the 'second pain') terminate on the dorsal horn of the spinal cord (fig.10B1.3.1). The first neuron ends here Almost certainly the synaptic transmitter is substance P (originally reported by the great pharmacologist Gaddum, together with von Euler in the 1930s), secreted by the terminals of the C as well as A fibers. 2. The path The tip of the dorsal horn ib called 'substantia gelatinosa Rolandf' (SCR, also written as SG). A fibers and C fibers terminate at SGR. From the SGR, the next order neurons arise and cross to the opposite side and form the 'spmothalamic tract' (STT, also called anterolateral system). (Details of the STT have been given in chap 3, sec XB1). In short, the STT reaches, ultimately, the thalamus. From the thalamus, the next order neuron arises to end in the sensory cortex in the parietal lobe. It is important to remember, that some descending fibers from the brain (vide below) terminate on the SCR. They constitute the tract that causes inhibition of pain. In the above description of the path of pain, it was assumed, that the pain arose from a somatic structure Under some conditions, pain can also arise from the viscera. Abdominal visceral pain are carried by afferent sympathetic fibers. These fibers enter the spinal cord travel up vianterolateral system (spmothalamic tract, STT) reach-the thalamus parietal lobe of the cortex. However, cortical representation of visceral (pain) sensation is rather poor. Pelvic splanchnic and vagus (both parasympathetic) are also known to carry visceral pain sensations. Thus, pelvic visceral pain is also carried by pelvic splanchnics. Visceral Pain A viscus is insensitive to most of the sensory stimuli (like touch, thermal sensations etc.). Thus, if a part of the intestine is exteriorized through an abdominal wound and touched, no sensation of touch is elicited. However, pain sensation can, under some conditions, arise from the viscera. Conditions, where the pain sensation can arise from the viscera are : (i) Ischemia. The classical example is coronary artery occlusion resulting in myocardial ischemia cardiac pain. (ii) Obstruction of a hollow viscus. The typical example is obstruction of a segment of large intestine. The part proximal to the obstruction contract violently (as if, it is trying to overcome the obstruction) and intestinal colic results. Actually the pain may be due to the spasm (sustained powerful contraction) of the smooth muscles; the spasm in turn produces ischemia of the muscles pain. Alternatively the violent contraction may cause traction of the mesentery, leading to pain. In the mesentry, there is severe overcrowding of nerves; this is because