Muscarinic receptors are coupled to the Gi subunit; therefore, vagal activation decreases cAMP. Gi-protein activation also leads to the activation of KACh channels that increase potassium efflux and hyperpolarizes the cells. Increases in vagal activities to the SA node decreases the firing rate of the pacemaker cells by decreasing the slope of the pacemaker potential (phase 4 of the action potential); this decreases heart rate (negative chronotropy). The change in phase 4 slope results from alterations in potassium and calcium currents, as well as the slow-inward sodium current that is thought to be responsible for the pacemaker current (If). By hyperpolarizing the cells, vagal activation increases the cells threshold for firing, which contributes to the reduction in the firing rate. Similar electrophysiological effects also occur at the AV node; however, in this tissue, these changes are manifested as a reduction in impulse conduction velocity through the AV node (negative dromotropy). In the resting state, there is a large degree of vagal tone on the heart, which is responsible for low resting heart rates. There is also some vagal innervation of the atrial muscle, and to a much lesser extent, the ventricular muscle. Vagus activation, therefore, results in modest reductions in atrial contractility (inotropy) and even smaller decreases in ventricular contractility. Muscarinic receptor antagonists bind to muscarinic receptors thereby preventing ACh from binding to and activating the receptor. By blocking the actions of ACh, muscarinic receptor antagonists very effectively block the effects of vagal nerve activity on the heart.
Treatment may be needed in adults who, while previously asymptomatic, begin to experience pain, lower back degeneration, scoliosis, neck and upper back problems and bladder control issues. Surgery on adults with minimal symptoms is somewhat controversial. For example, a website from the Columbia University Department of Neurosurgery says, "For the child that has reached adult height with minimal if any symptoms, some neurosurgeons would advocate careful observation only." However, surgery for those who have worsening symptoms is less controversial. If the only abnormality is a thickened, shortened filum, then a limited lumbosacral laminectomy with division of the filum may be sufficient to relieve the symptoms.This syndrome was first noticed in the late 19th century. While information has been available for years, little widespread blind research has been done. More research has been called for, and doctors have conducted many studies with good results. There is a low morbidity rate, and no complications have been documented other than those typical of any type of back surgery. The association of this condition with others has been noticed, and needs further research to understand such relationships. TCS is causally linked to Chiari malformation and any affirmative diagnosis of TCS must be followed by screening for Chiaris several degrees. TCS may also be related to Ehlers–Danlos syndrome, or Klippel–Feil syndrome, which should also be screened for upon a positive TCS diagnosis. Spinal compression and the resulting relief is a known issue with this disorder.