Irritable bowel syndrome (IBS) is a large array of disorders described as abdominal discomfort and pain with changes in bowel. IBS is known for cramping, abdominal pain, bloating gas, diarrhea and constipation. The colon’s many nerves connect it to the brain and are partly controlled by the ANS, which reacts to stress similar to the heart.
The ascending pathways dealing with pain consist of three different tracts: the neospinothalamic, the paleospinothalamic, and the archispinothalamic tracts. The dorsal root ganglion is where the first-order neurons are located in all three tracts. Each tract starts in different spinal regions and terminates in a different area in the brain.
The neospinothalamic tract is a lateral spinothalamic tract and synapses very little. Each nociceptive neuron has a single axon that divides into two, sending one end to innervate with tissue and the other into the dorsal horn. The A-delta fibres (carrying fast pain and provides information of the exact location of the stimulus) and C-fibres (carrying slow pain) terminate on the dorsal horn. The A-delta fibers terminate and excite the 2nd order neurons. The long fibres discuss immediately through the anterior commissure and off to the brain. Most of the pain fibers below the neck terminate in the ventroposterolateral (VPL) nucleus and ventroposteroinferior (VPI) nucleus of the thalamus, which is a relay station that sends the signals to the primary somatosensory cortex. The A delta fibers terminate in the ventroposteromedial (VPM) thalamus and are somatotopical.
Visceral organ’s nociceptors respond to stimulations such as pressure, tissue damage, and chemical (gastrointestinal lesions and/or tumors). Free nerve endings are scattered and any stimulus that excites these endings cause pain. Such stimuli include spasm of the smooth muscle, distention, or stretching of the ligament. This pain is not localized; rather it is a distant site. Dangerous warning signs or circumstances are important, nociceptor pathways are involved in transmitting these signals and some are made redundant.
Pain activates many brain areas, such as sensation, perception, emotion, memory and motor reaction. Part of the dorsal horn contains enkephalinergic interneurons and other inhibiting neurons involved in pain. Descending pathways containing serotonin and norepinephrine, which activate some inhibitory local circuits.
Multiple websites say researchers believe the key to better IBS treatment lies in “tweaking neurotransmitters and hormones related to gastrointestinal motility and sensation”.
Doctors may prescribe antidepressants. Low doses of antidepressants block signals of pain to the brain called tricyclic antidepressants, such as Pamelor, Elavil, and Tofranil. Common side effects include dry mouth, blurred vision, and constipation. Others cause diarrhea, such as Celexa, Paxil, and Prozac. Antispasmodic, such as Levbid or Bentyl, "relax the smooth muscle of the gut," Side...