What are the somatic and autonomic nerves that innervate the penis?

Penis Innervation

The penis receives dual innervation: autonomic (sympathetic and parasympathetic) nerves control erectile function via the cavernous nerves, while somatic sensory and motor innervation is provided by the pudendal nerve and its dorsal nerve branch.

Autonomic (Visceromotor) Innervation

The autonomic nervous system provides the primary control for erectile function through a complex interplay of sympathetic and parasympathetic pathways 1, 2:

Parasympathetic Pathways (Pro-Erectile)

• Sacral parasympathetic nerves (S2-S4) are the primary pro-erectile pathway, traveling via the pelvic plexus to form the cavernous nerves that innervate erectile tissue 3
• These pathways cause relaxation of smooth muscle cells in erectile tissue and penile arteries, leading to blood engorgement and tumescence 4
• The parasympathetic system provides both excitatory and inhibitory innervation affecting genital vasocongestion 2

Sympathetic Pathways (Anti-Erectile)

• Sympathetic innervation (T11-L2) is generally inhibitory to erection, except during ejaculation 3
• Sympathetic pathways are anti-erectile during the flaccid state but become activated during the emission phase of ejaculation 4

Regional Distribution

• Proximally, the intracavernosal sector is predominantly supplied by autonomic (nitrergic) fibers 5
• Distally, autonomic innervation diminishes except along intrapenile vascular anastomoses, where mixed autonomic and somatic fibers travel together 5
• This creates a functional division: a proximal segment guaranteeing erectile rigidity and a distal sensory segment 5

Somatic (Sensory and Motor) Innervation

Pudendal Nerve and Branches

• The pudendal nerve (S2-S4) provides somatic sensory innervation primarily through the dorsal nerve of the penis 6, 7
• Proximally, the extra-albugineal (outer) sector of the penis is mainly supplied by somatic nerve fibers 5
• Genital afferent stimulation via pudendal pathways excites spinal autonomic nuclei and supraspinal sexual centers, playing an essential role in erectile function, penile rigidity, ejaculation, and sexual arousal 6

Motor Function

• The pudendal nerve innervates the ischiocavernosus and bulbospongiosus muscles, which are perineal striated muscles 4
• Contraction of the ischiocavernosus muscles provides additional penile rigidity during erection 4, 3
• The bulbospongiosus muscle produces rhythmic contractions during the expulsion phase of ejaculation 4

Critical Anatomic Communication Points

Autonomic and somatic pathways communicate at three distinct levels 7:

1. Proximal supralevator level - in the pelvis near the pelvic plexus
2. Intermediate intralevator level - within the levator ani muscles
3. Distal infralevator level - where cavernous nerves interact with branches of the dorsal nerve

Distal Nitrergic Communication

• The distal dorsal nerve becomes nitrergic (nNOS-positive) through interaction with autonomic cavernous nerves 7
• This distal communication extends nitrergic (nitric oxide-mediated) activity to the distal cavernous bodies, which is critical for erectile function 7
• Pudendal nerve branches are nitric oxide synthase positive and communicate with cavernous nerves 6

Clinical Implications

Surgical Considerations

• Care must be taken during pelvic or reconstructive surgery to preserve the three levels of autonomic-somatic communication, particularly the distal interaction between cavernous and dorsal nerves 7
• Cancer treatments directed toward the pelvis can damage blood vessels and the autonomic nervous system, resulting in higher rates of erectile dysfunction 1

Functional Integration

• Spinal autonomic centers controlling erection depend on input from both supraspinal centers and genital afferents 6, 3
• Sensory information from the genitals is a potent activator of pro-erectile spinal neurons and can elicit reflexive erections 3
• Multiple spinal reflexes modulated by genital afferents coordinate erectile function and micturition 6