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Somatomotor penile innervation originates in Onuf’s nucleus in the S2-4 spinal segments.

These nerves travel to the ischiocavernosus and bulbocavernosus muscles when activated lead to contraction necessary for the rigid-erection phase.

Several animal studies show that stimulation of the somatomotor pathways may also be under sympathetic control, and adrenergic stimulation may lead to contraction of these muscles during ejaculation (13,14).

Somatomotor spinal reflexes may also be initiated by genital stimulation. For instance, the well-known bulbocavernosus reflex is evidence this reflex exists; however the clinical significance of its absence in the neurological assessment of ED has not been substantiated (15). Erections are initiated and maintained via integration of afferent inputs in the supra sacral regions of the central nervous system.

Regions of the brain cited to have key roles in the integration of signals include the medial amygdala, MPOA,

periaqueductal

Studies in animal models, particularly in rats, have been paramount in identifying these key areas of signal integration and control. Electrostimulation of the MPOA, PVN and hippocampus lead to erection and lesions in these areas may prevent erection (17). injected labeled pseudorabies virus into rat corpora cavernosa and traced them to neurons in the spinal cord, brain stem and hypothalamus (18).

Stimulation

Axonal tracing in animals have shows direct projections from the hypothalamus to the lumbosacral autonomic erection centers.

Oxytocin and vasopressin have been identified as central neurotransmitters within the hypothalamic nuclei and may have a role in penile erection (17). These signaling studies identifying key areas of erectile response integration may explain how ED is associated with cerebrovascular accident (CVA), Parkinson’s, epilepsy and MS. The supraspinal pathways are likely activated via central neural activation during sexual arousal.

Positron emission tomorgraphy (PET), and functional magnetic resonance imaging (fMRI) have led to a greater understanding to which center are activated during arousal. These imaging studies measure increases in cerebral blood flow or changes in cerebral activity on a real-time basis.

Studies are performed when male subject are aroused by visual cues (usually sexual explicit photos or videos) and compared to images obtained during exposure to sexually neutral cues differences can be measured.

Several studies have identified that the inferior frontal lobes, inferior temporal lobes and insular gyrus, and occipital lobes are involved with processing arousal cues, although each are likely to process different stimuli (20-23).

Spinal cheapest price for sildenafil 20 mg cord injury (SCI) ED is a common occurrence after SCI, occurring in up to 80% of men, and results from disruption of the nerve pathways essential for erection (24,25). Different degrees of ED may occur depending on the spinal cord level of injury (LOI), extent of lesion and timing from injury. Reflexogenic erections can occur with lesions above L3 or L4 when the erectile spinal reflex arc remains intact.

Psychogenic erections can occur with low lesions in the sacral and lumbar spinal cord but may not occur in complete lesions above T9 that can damage sympathetic outflow.

Additionally, reflexogenic erections are not likely to occur in the spinal shock period that occurs after the initial cord trauma. Conversely, their occurrence may signal that the period of shock is over (26).

Typically SCI affects younger men in their “sexual prime” and ED is associated with decreased quality of life (27). Cerebrovascular accident (CVA/stroke) A CVA can occur anywhere through the brain, midbrain, brainstem and spinal cord leading to varying degrees of SD depending on location. A decline in libido, erection and ejaculation are frequent in men who have had a CVA, with a reported prevalence of ED that varies from 17% to 48% (28,29).

Right hemispheric infarcts seem to affect erections more so than left-sided ones. The exact effects of CVA on sexual function are complex and multifactorial, as disability, psychological and emotional status can affect sexual function aside from the location of the CVA.

ED varies in men with seizure disorders, occurring in 3% to 58% of men with epilepsy (30).

The cause of ED is likely multifactorial, with neurologic, endocrine, sildenafil cipla price iatrogenic, psychiatric and psychosocial factors leading to varying degrees of fake prescription for viagra ED (31). ED can occur in periods surrounding active seizures (ictal) or in the periods unrelated to seizure activity (post-ictal) as well (32).

Multiple sclerosis (MS) ED occurs in up to 70% of men with MS, and MS is one of the most prevalent neurological disorders that affect the younger adult population worldwide (33-35).

The mean time for SD and ED to develop is about 9 years and is rarely a presenting symptom of MS (36). Men with MS and ED may continue to have nocturnal erections, and psychogenic erections; however, this does not mean they have psychogenic ED but could be an indicator that MS involves the spinal cord (37). Primary SD is due directly due to MS-related neurological deficits, secondary SD is related to physical impairments and symptoms or drugs used for MS treatment, lowest price sildenafil and tertiary SD is due to the psychological, social and cultural problems attributed to MS (38).

These classifications are important, and underscore the importance of addressing all the issues leading to SD not just the neurologic impairment.

Parkinson’s disease (PD) PD is a chronic neurodegenerative disease characterized by “motor” and “non-motor” symptoms that lead to progressive disability. Erectile and SD are “non-motor” symptoms and can occur in 50–69% of males with PD (39-42).

Ejaculatory and orgasmic function are also impaired.

PD affects the dopaminergic pathways leading to erection and arousal. Dopaminergic therapy for PD can improve ED, and sometimes therapy may lead to hypersexuality (43,44).

A comparison of married men with PD to age matched controls with non-neurologic chronic disease such as arthritis did not show any discrepancy in ED rates (45).

This suggests that ED in certain groups with PD may occur from disease related factors common in chronic illness, in general.

Multiple system atrophy (MSA) MSA is a neurodegenerative disease of undetermined etiology, where ED is an early prominent sign occurring in 40% of men at the time of diagnosis (46,47). ED occurs in the majority of patients and the exact cause of it is unknown (48). Like PD, MSA likely affects the dopaminergic pathways within the brain essential for arousal (49). Orthostatic hypotension (OH) as a causal factor has been refuted by evidence that sildenafil can overcome reduced filling pressures, and the ED usually precedes the development of OH (46,49,50).

Similar to other neurologic disorders that lead to ED, other disease related factors such as psychosocial stress, the burden of chronic illness, changed appearance, fatigue, decreased fine motor movement of fingers, immobility and diminished self-esteem due to loss of independence may contribute as well (51).

Spina bifida (SB) SB is a group of developmental abnormalities resulting from neural tube closure defects, and affects less than 1/1,000 live births (52).