Neurons for Ejaculation and Factors Affecting Ejaculation

Abstract

Ejaculation is a reflex and the last stage of intercourse in male mammals. It consists of two coordinated phases, emission and expulsion. The emission phase consists of secretions from the vas deferens, seminal vesicle, prostate, and Cowper's gland. Once these contents reach the posterior urethra, movement of the contents becomes inevitable, followed by the expulsion phase. The urogenital organs are synchronized during this complete event. The L3-L4 (lumbar) segment, the spinal cord region responsible for ejaculation, nerve cell bodies, also called lumbar spinothalamic (LSt) cells, which are denoted as spinal ejaculation generators or lumbar spinothalamic cells [Lst]. Lst cells activation causes ejaculation. These Lst cells coordinate with [autonomic] parasympathetic and sympathetic assistance in ejaculation. The presence of a spinal ejaculatory generator has recently been confirmed in humans. Different types of ejaculatory dysfunction in humans include premature ejaculation (PE), retrograde ejaculation (RE), delayed ejaculation (DE), and anejaculation (AE). The most common form of ejaculatory dysfunction studied is premature ejaculation. The least common forms of ejaculation studied are delayed ejaculation and anejaculation. Despite the confirmation of Lst in humans, there is insufficient research on animals mimicking human ejaculatory dysfunction.

Keywords: ejaculation; ejaculatory dysfunctions; lumbar spinothalamic cells; spinal ejaculatory generator.

Figure 1

Schematic diagram of level of spinal cord and neurons regulating ejaculation. Activated spinal ejaculation generator directs and synchronizes the activity of: (a) parasympathetic output that innervate prostate and seminal vesicles secreting seminal fluid. (b) Sympathetic output that innervate smooth muscle cells of the seminal tract and the bladder neck. Contraction of the seminal tract accumulate spermatozoa that is mixed with the seminal fluid to the prostatic urethra. The neck of bladder remains closed to prevent retrograde ejaculation. (c) Somatic output that innervate the pelvic striated muscles (not shown in this figure). The external urethral sphincter relaxes and rhythmic contractions of the bulbospongiosus and ischiocavernosus muscles are responsible for rhythmic forceful expulsion of sperm at the urethral meatus. (a) and (b) = emission; (c) = expulsion.

Figure 2

Schematic diagram of organs involved in ejaculation. Anterograde ejaculation (green arrow) and retrograde ejaculation (black arrow) shown in same figure, retrograde ejaculation is due to the inability of the neck of bladder to close completely during expulsion phase. Some amount of semen can be seen in the urinary bladder.

Figure 3

Table showing the normal and abnormal types of ejaculation. Their etiologies are described in brief.