Neurons from the
PVN run down through the mid-brain, and at this level the nucleus
paragigantocellularis can interrupt proerectile signals from higher brain
regions if it becomes inappropriate to have an erectile response, this is
mediated through a serotinergic mechanism although the receptor subtypes
involved are not fully elucidated. (Marson and McKenna, 1990 and 1992).Once
through the mid-brain, the erectile signals pass along the spinal cord to the
periphery. In addition to transmitting neural signals, the spinal cord has an
integrative role of processing signals from peripheral and higher central
regions. There are two main sites of integration for erectile function in the
spinal cord, the sacral erection spinal centre from S2 to S4 and a thoracic-based
centre from T11 to L2,
(Giuliano et al., 1995). Erectile signals leave
the CNS at these two centers, and the information is then transferred through
autonomic neurons to the periphery.