Fig. 4

Diagram showing the involvement of the sphenopalatine ganglion (SPG) in the physiopathology of trigeminoautonomic headaches. The afferent part of this loop is mediated by the trigeminal nerve, which sends nociceptive signals from the dural blood vessels to the trigeminocervical complex. This information projects to higher brain structures, resulting in cephalic pain. The efferent part of this loop conveys mostly through the superior salivatory nucleus, exiting the brain stem via the facial nerve and reaching the sphenopalatine ganglion through the greater petrosal nerve. Postganglionic fibres exit the sphenopalatine nerve towards the dural vessels, closing the loop. Blocking the SPG might reduce the afferent input of signals towards the trigeminal system and reduce the activation of the trigeminocervical complex. CNS: central nervous system