Onuf's nucleus, one on the right and one on the left side, is located at the front/most ventral in the anterior horn segment of the spinal cord S2 (sometimes also S1s). The core consists of approx. 600pcs small to medium somatic motor neurons. The axons of the neuff nucleus leave the spinal cord and vertebral canal and are then part of the nervus pudendus (which innervates the muscles of the pelvic floor, the perineum skin, and the musculature and skin of the external genitalia).
The man's Onuf core is clearly larger than the woman's.
It is the task of the Onuf core to check:
1/ Musculus sphincter ani externus; a volitional striated muscle to keep the opening closed.
2/ Musculus sphincter urethrae; a volitional striated muscle designed to keep the bladder's transition to the urethra closed.
3/ Musculus bulbospongiosus and musculus ischiocavernosus; striated muscles which, especially in men, are important for erection and ejaculation.
Disturbances in the function of the Onuf nucleus lead with respect to 1/ and 2/ above to urinary and faecal incontinence respectively and with respect to 3/ to disorders of sexual function.
Incontinence = inability to "hold tight" (here with respect to urine and/or feces).
The nucleus has a comparatively very strong influx of dopaminergic nerve signals from cell group A11 into the mesencephalon.
Remarkable and startling is the fact that the motor neurons of the Onuf nucleus are uniquely resistant in the motor neuron degeneration that underlies the disease ALS (Amyotrophic Lateral Sclerosis).