- Mnemonic: “Point, Squeeze, and Shoot”
- Point = Erection (Parasympathetic)
- Squeeze = Emission (Sympathetic)
- Shoot = Ejaculation (Somatic + Sympathetic)
- Somatic Innervation
- Pudendal Nerve (S2-S4)
- Mnemonic: “S2, 3, 4 keeps the penis/pelvis off the floor.”
- Sensory: Provides sensation to the perineum, glans penis, and clitoris. Afferent limb of sexual response.
- Motor: Innervates external urethral sphincter, external anal sphincter, and bulbospongiosus/ischiocavernosus muscles.
- Clinical Correlate:
- Pudendal nerve block: Anesthetic injected near the ischial spine to provide perineal anesthesia during childbirth.
- Involved in the “shoot” phase (ejaculation) via rhythmic contraction of pelvic floor muscles.
- Autonomic Innervation: Erection (Male & Female)
- Parasympathetic Nervous System (“Point”)
- Origin: Pelvic splanchnic nerves (S2-S4).
- Neurotransmitter: Nitric Oxide (NO).
- Mechanism:
- NO activates guanylate cyclase → ↑ cGMP.
- ↑ cGMP → smooth muscle relaxation in corpus cavernosum arterial walls.
- Arterial vasodilation → engorgement of erectile tissue with blood.
- Pharmacology: PDE-5 inhibitors (e.g., Sildenafil) prevent the breakdown of cGMP, prolonging vasodilation and erection.
- Autonomic Innervation: Emission & Ejaculation (Male)
- Sympathetic Nervous System (“Squeeze”)
- Origin: Hypogastric nerve (T11-L2).
- Function (Emission): Stimulates contraction of the epididymis, ductus deferens, seminal vesicles, and prostate gland, moving semen into the prostatic urethra.
- Sympathetic + Somatic (“Shoot”)
- Sympathetic: Causes closure of the internal urethral sphincter to prevent retrograde ejaculation.
- Somatic (Pudendal n.): Causes rhythmic contraction of the bulbospongiosus muscle to expel semen.
- Detumescence (return to flaccid state): Mediated by sympathetic fibers (T11-L2). Norepinephrine release from sympathetic nerve endings causes vasoconstriction of the helicine arteries and contraction of trabecular smooth muscle, forcing blood out of the corpora cavernosa.