Health

To understand the changes in sexual function after spinal cord injury (SCI), we must appreciate the complex neural networks that coordinate our vascular and endocrine systems allowing sexual pleasure. Over 3 decades ago, the “human sexual response cycle” was described to occur in four phases:

1. Excitement phase
2. Plateau phase
3. Orgasm phase
4. Resolution phase

For men without SCI, the excitement phase begins with stimulating thoughts from the brain (psychogenic) or by manual tactile stimulation of the genitalia (reflexogenic). This information is translated to the blood vessels within the penis by different parts of our nervous system, causing vasocongestion (pooling of blood), leading to an erection.

The sympathetic nervous system, via the T11 to L2 spinal nerves, is responsible for a psychogenic erection by translating pleasurable thoughts from the brain to the male genitalia.

 So, essentially, the spinal cord is the information highway between the brain and the rest of the body. Alternatively, a reflexogenic erection can occur without involving input from the brain through a reflex pathway. In other words, direct stimulation of the penis sends sensory information to the parasympathetic nervous system, via the S2-S4 spinal nerves, which triggers a response back to the penis leading to an erection. Ideally, to create a firm and lasting erection for intercourse, these two types of erections usually work together. As the plateau phase approaches, seminal fluid secretions start flowing into the urethra in preparation for ejaculation during the orgasm phase. This phase is dependent on coordination between the sympathetic nervous system (T11-L2), which closes the bladder neck to prevent the ejaculate from going retrograde (backward) into the bladder, and the parasympathetic nervous system (S2-4), which causes tiny muscle contractions to project the semen anterograde (forward) out of the penis. The cycle concludes with the resolution phase when the sympathetic nervous system creates an outflow of the pooled blood to return the penis to the flaccid state.

Analogous physiologic changes occur in women without SCI. Vasocongestion and lubrication of the vagina and external genitalia start the excitement phase by psychogenic and/or reflexogenic stimulation (initiated by similar spinal nerves described above). Vaginal lubrication ensues as a result of blood pooling and is considered the “erection” counterpart in women. Continuing on to the plateau phase, the breasts and nipples enlarge as the vasocongestion builds. At this point, the women’s cycle is unlike the men’s progression of sequential phases. From the plateau phase, women can move back and forth to and from the orgasm phase, allowing for multiple orgasms, or conclude with the resolution phase.

Predictors of Sexual Function after SCI