The anal reflex represents a foreign reflex at the external anal sphincter originating from spinal cord segments S3 to S5. It is an identification reflex for examining the transmission of stimuli in the superficial perineal nerve. An absent reflex may indicate dysfunction of corresponding nerve pathways.
What is the anal reflex?
The anal reflex characterizes a foreign reflex, which is triggered by touching the skin of the anus in the form of contraction of the external sphincter. The anal reflex characterizes a foreign reflex, which is triggered when touching the skin of the anus in the form of contracting the external sphincter. This also involves touching the perineum as well as the areas of the supply area of the superficial perineal nerve. In the same reflex chain, the root of the penis or vulva is also involved. Their touch leads to contraction of the bulbospongiosus muscle. An older name for the anal reflex is therefore also the bulbospongiosus reflex. Altogether, the anal reflex circumscribes the reflex-like reaction of the entire supply area of the spinal cord segments S3 to S5. In the case of an extraneous reflex, the reflex response does not occur in the organ that received the stimulus. There is a reflex arc that transmits the stimulus through multiple synapses. Thus, when the anus skin or the entire supply area of the superficial perineal nerve is touched, the stimulus is transmitted to the brain. From there, information processing generates a reflex response by contraction of the external sphincter.
Function and task
The anal reflex is a response from the supply area of the superficial perineal nerve (pudendal nerve). The pudendal nerve, also called the pudendal nerve, belongs to the lumbosacral plexus. It arises from the area of the spinal cord segments S1 to S4. In this, it represents a subsection of the lumbar-cruciate plexus and is also called the pudendal plexus. The pudendal nerve runs caudoventrally to the pelvic floor and enters the Alcock’s canal through the great ischial hole (foramen ischiadicum majus). The Alcock’s canal (Canalis pudendalis) is a canal in the area of the pelvic floor, which is considered a passage for various conduction structures. The pudendal nerve again divides into several branches. These are the nervi rectales inferiores, the nervi perineales and the nervus dorsalis penis or the nervus dorsalis clitoridis. The nervi rectales inferiores (lower rectal nerves) supply the area of the anus and the external sphincter. The nervi perineales, in turn, supply the perineum, the bulbospongiosus muscle, and the urethralis muscle (striated muscle of the urethra). In addition, they also sensitively innervate the scrotum and labia. According to this account, the anal reflex is a partial reflex of a larger complex, since the pudendal nerve as a whole, with its three branches, supplies a larger area in the anal and genital regions. Reflexes are natural responses to stimuli. The anal reflex (contraction of the external sphincter) is triggered during sexual acts by touching the erogenous zones to avoid defecation in the process. The same applies to urinary retention during sexual intercourse. External reflexes, however, have the property of also being influenceable by will. Thus, the reflex can be strengthened or weakened. The purpose of triggering the reflex during examination is to check the function of the pudendal nerve.
Diseases and complaints
If the anal reflex is absent, this indicates neurologic disorders. Dysfunction or injury to the inferior rectal nerves can lead to incontinentia alvi, among other symptoms. Damage to the nervi perineales in turn leads to paralysis of the urethralis muscle. As a result, urinary incontinence occurs. Incontinentia alvi is fecal incontinence. In this case, the anal sphincter no longer functions properly. There are many causes for this. In order to trigger fecal incontinence, several factors usually have to come together. The failure of only one control mechanism is not sufficient for defecation, because in these cases compensatory mechanisms are triggered. Responsible for proper defecation is the continence organ (closure apparatus of the anus). This organ includes, among others, the internal and external sphincter muscles. However, the external sphincter can be consciously contracted, even when there is a strong need to defecate. This forces the intestinal contents back into the rectum.Although failure of the anal reflex does not necessarily lead to fecal incontinence, it is a serious indication of a possible underlying disease that suppresses the transmission of impulses from the spinal cord to the pelvic area. In addition to direct sphincter disorders, there are several anal reflex-related causes of fecal incontinence. These include impulse processing disorders, interruption of impulse transmission, sensory disorders, and psychological disorders. Impulse processing is disrupted by diseases such as Alzheimer’s disease, stroke, multiple sclerosis, or brain tumor, among others. In these diseases, incoming impulses in the brain may no longer be processed, causing the anal reflex to fail. Interruption of impulse transmission occurs in paraplegia, multiple sclerosis or neural tube malformation (spina bifida), among others. In sensory disorders, sensory perception is prevented, for example, by protrusion of the intestinal mucosa or hemorrhoids, so that no signal at all is sent for the anal reflex. The anal reflex can also fail in mental disorders and psychoses. Urinary incontinence can also be caused by a reflex disorder. For example, paraplegia, multiple sclerosis or other diseases also play a role here for the lack of reflex contraction of the urethral muscle. Thus, both fecal incontinence and urinary incontinence may be caused by reflex dysfunction of the pudendal nerve.
