To break the Autonomic Nervous system down…
Parasympathetic nervous system
The parasympathetic nervous system (PSNS) is one of the two main divisions of the autonomic nervous system (ANS). The ANS is responsible for regulation of internal organs and glands, which occurs unconsciously. To be specific, the parasympathetic system is responsible for stimulation of “rest-and-digest” activities that occur when the body is at rest, including sexual arousal, salivation, lacrimation (tears), urination, digestion, and defecation. Its action is described as being complementary to that of one of the other main branches of the ANS, the sympathetic nervous system, which is responsible for stimulating activities associated with the fight-or-flight response.
Sympathetic nervous system
Alongside the other two components of the autonomic nervous system, the sympathetic nervous system aids in the control of most of the body’s internal organs. Stress—as in the flight-or-fight response—is thought to counteract the parasympathetic system, which generally works to promote maintenance of the body at rest.
The sensory arm is made of “primary visceral sensory neurons” found in the peripheral nervous system (PNS), in “cranial sensory ganglia”: the geniculate, petrosal and nodose ganglia, appended respectively to cranial nerves VII, IX and X. These sensory neurons monitor the levels of carbon dioxide, oxygen and sugar in the blood, arterial pressure and the chemical composition of the stomach and gut content. (They also convey the sense of taste, a conscious perception). Blood oxygen and carbon dioxide are in fact directly sensed by the carotid body, a small collection of chemosensors at the bifurcation of the carotid artery, innervated by the petrosal (IXth) ganglion. Primary sensory neurons project (synapse) onto “second order” or relay visceral sensory neurons located in the medulla oblongata, forming the nucleus of the solitary tract (nTS), that integrates all visceral information. The nTS also receives input from a nearby chemosensory center, the area postrema, that detects toxins in the blood and the cerebrospinal fluid and is essential for chemically induced vomiting or conditional taste aversion (the memory that ensures that an animal which has been poisoned by a food never touches it again). All these visceral sensory informations constantly and unconsciously modulate the activity of the motor neurons of the ANS
Sympathetic nervous system
Main article: Sympathetic nervous system
-Promotes a “fight or flight” response, corresponds with arousal and energy generation, and inhibits digestion.
-Diverts blood flow away from the gastro-intestinal (GI) tract and skin via vasoconstriction.
-Blood flow to skeletal muscles and the lungs is enhanced (by as much as 1200% in the case of skeletal muscles).
-Dilates bronchioles of the lung, which allows for greater alveolar oxygen exchange.
-Increases heart rate and the contractility of cardiac cells (myocytes), thereby providing a mechanism for the enhanced blood flow to skeletal muscles.
-Dilates pupils and relaxes the ciliary muscle to the lens, allowing more light to enter the eye and far vision.
-Provides vasodilation for the coronary vessels of the heart.
-Constricts all the intestinal sphincters and the urinary sphincter.
Parasympathetic nervous system
Main article: Parasympathetic nervous system
-Promotes a “rest and digest” response, promotes calming of the nerves return to regular function, and enhances digestion.
-Dilates blood vessels leading to the GI tract, increasing blood flow. This is important following the consumption of food, due to the greater metabolic demands placed on the body by the gut.
-The parasympathetic nervous system can also constrict the bronchiolar diameter when the need for oxygen has diminished.
-Dedicated cardiac branches of the Vagus and thoracic Spinal Accessory nerves impart Parasympathetic control of the Heart or Myocardium.
-During accommodation, the parasympathetic nervous system causes constriction of the pupil and contraction of the ciliary muscle to the lens, allowing for closer vision.
-The parasympathetic nervous system stimulates salivary gland secretion, and accelerates peristalsis, so, in keeping with the rest and digest functions, appropriate PNS activity mediates digestion of food and indirectly, the absorption of nutrients.
-Is also involved in erection of genitals, via the pelvic splanchnic nerves 2–4.
-Stimulates sexual arousal.
Effects of Spinal Cord Injury on Semen Parameters
Neurogenic reproductive dysfunction in men with spinal cord injury (SCI) is common and the result of a combination of impotence, ejaculatory failure, and abnormal semen characteristics. It is well established that the semen quality of men with SCI is poor and that changes are seen as early as 2 weeks after injury. The distinguishing characters of poor quality are abnormal sperm motility and viability. In the majority of the men with SCI, the sperm count is not abnormal. We elaborate on the effects of the SCI on semen parameters that may contribute to poor motility and poor viability.
Section of the study called Testicular Function
Experimental work on acute SCI in rats shows profound effects on the hypothalamic-pituitary-testicular axis by the third day after SCI (19). These changes were temporary, and a normal hormonal milieu was restored by 14 days. The overall conclusion from animal studies rules out hormonal deficiency as the predominant cause of infertility in SCI. Hypothalamic-pituitary-testicular axis dysfunction has been confirmed in humans after SCI, and its severity has been correlated to the level of injury (20). Testosterone, follicle-stimulating hormone, and leuteinizing hormone levels remained altered for 6 weeks in men with paraplegia and for 4 months in men with tetraplegia. Similar dysfunction was also apparent in the HP-adrenal axis with abnormal cortisol secretion in response to adrenocorticotropic hormone in men with SCI (21). Overall, 51% of men with SCI have at least one hormonal abnormality and 86% have some hypothalamic-pituitary axis abnormality (22). Hyperprolactinemia is seen very commonly in SCI and might be contributory to testicular hypofunction (23,24). Although abnormal hormonal levels in urine and blood have been reported in many studies in men with SCI, this does not seem to be the primary cause of infertility because equal numbers of studies report normal findings (25–27).
Historically, nearly 65% of men with SCI have abnormal spermatogenesis on testicular biopsy, and the abnormality is generally independent of duration, level, and severity of the injury (27) Testicular interstitial fibrosis and arrest of spermatogenesis have been reported (27,28). Using quantitative micrometric assessment, researchers found that 65% of men with SCI, compared with noninjured fertile controls, had adequate mean spermatid numbers per tubule that met minimum standards for adequate spermatogenesis (29). However, as a group they had significantly decreased numbers per tubule (30). Hirsch et al noted improvements over the decades in testicular biopsies of men with SCI. He hypothesized that the improvements were related to better bladder management over the decades, including an emphasis on low-pressure voiding (31).
Conclusion to the above study
Overall, 51% of men with SCI have at least one hormonal abnormality and 86% have some hypothalamic-pituitary-testicular axis abnormality (21). Despite these abnormal hormonal levels, it does not seem to be the primary cause of infertility in men with SCI, because an equal number of studies report normal results. Males with obstructive azoospermia have similar quantitative parameters of spermatogenesis as that seen in men with SCI, pointing to a postspermatogenic cause for neurogenic infertility. Epididymal function appears sensitive to temperature change and also sensitive to sympathetic nerve integrity; however, there appears to be no correlation between scrotal temperature and quantitative semen parameters of men with SCI.
Maintenance of sperm function requires normal secretions from prostate and seminal vesicles. Dysfunction at this level might result in subfertility. The balance between ROS production and scavenging in men with SCI appears abnormal and may be responsible for infertility. Men with SCI have elevated levels of ROS in their semen. This increase in ROS seems to be at least in part due to an increased oxidative stress and leucocytospermia. There is a correlation between the percentage of patients with normal spermatogenesis and the improvement in bladder management and infection control (31). Semen infection appears to have no effect on sperm count or pregnancy rates. The responsibility for poor sperm motility and viability in SCI seems to have shifted towards the constituents of the seminal plasma.
Autonomic nervous dysfunction seems to affect movement of sperm from the caudal epididymis and proximal vas. Although this may not affect the intrinsic motility of the sperm, it may have an impact on final mature movements. In addition, there is considerable neurogenic impairment to the ejaculation process that requires assisted ejaculation techniques.
The definitive causal mechanism leading to abnormal semen quality in men with SCI remains to be elucidated.
Obviously the injuries in this study are different to ours, i am using it to show the effect the nervous system has on the reproductive system.
You can probably work out what i am getting at, Finasteride has caused damage to the Peripheral nervous system, by the looks more specifically the autonomic nervous system due to the partial inhibition of Palmitoylethanolamide (PEA), among other things a neuroprotective compound.