Because PFM function is intimately connected to pelvic organ function, it is proposed that all sensory information from the pelvic region is relevant for PFM neural control. The sensory neurons are bipolar. Their cell bodies are in spinal ganglia. They send a long process to the periphery and a central process into the spinal cord where it terminates segmentally or – after branching for reflex connections – ascends in some cases as far as the brainstem.
The afferent pathways from the anogenital region and pelvic region are divided into somatic and visceral. Somatic afferents derive from touch, pain and thermal receptors in skin and mucosa and from proprioceptors in muscles and tendons. (Proprioceptive afferents arise particularly from muscle spindles and Golgi tendon organs.) The visceral afferents accompany both parasympathetic and sympathetic efferent fibers. The somatic afferents accompany the pudendal nerves, the levator ani nerve and direct somatic branches of the sacral plexus. The different groups of afferent fi bres have different reflex connections, and transmit at least to some extent different afferent information.
The terminals of pudendal nerve afferents in the dorsal horn of the spinal cord are found ipsilaterally, but also bilaterally, with ipsilateral predominance. The proprioceptive afferents form synaptic contacts in the spinal cord and have collaterals (‘primary afferent collaterals’), which run ipsilaterally in the dorsal spinal columns to synapse in the gracilis (dorsal column) nuclei in the brainstem. This pathway transmits information about innocuous sensations from the PFM.
The lateral columns of the spinal cord transmit information concerning pain sensations from perineal skin, as well as sexual sensations. In humans this pathway is situated superfi cially just ventral to the equator of the cord and is probably the spinothalamic tract.
The spinal pathways that transmit sensory information from the visceral afferent terminations in the spinal cord to more rostral structures can be found in the dorsal, lateral, and ventral spinal cord columns.