Male Reproductive System | Erection & Ejaculation

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Ninja Nerds!
In this reproductive physiology lecture, Professor Zach Murphy explains the complex neural and vascular mechanisms behind erection and ejaculation, key components of the male sexual response. This lecture integrates the roles of the autonomic nervous system, vascular dynamics, and smooth muscle signaling to give you a clear understanding of how these processes function and interact.

We begin by detailing how parasympathetic stimulation (S2–S4) initiates an erection by promoting nitric oxide (NO) release, which activates guanylate cyclase, increases cGMP, and leads to vasodilation of penile arterioles and engorgement of the corpora cavernosa. You’ll also learn how PDE-5 inhibitors like sildenafil enhance this process by preventing cGMP breakdown.

The lecture then transitions to ejaculation, which is mediated by sympathetic output (T11–L2). We discuss the two coordinated phases: emission, involving contraction of the vas deferens and seminal vesicles to deliver semen into the urethra; and expulsion, driven by rhythmic contraction of pelvic floor muscles under somatic control (pudendal nerve).

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