Bulbocavernosus Reflex

Bulbocavernosus Reflex diagram

What is Bulbocavernosus Reflex?

Bulbocaverosus reflex (BCR) is a polysynaptic reflex which is used to test for the presence of spinal shock and is basically used to identify and record the presence of a spinal cord injury or neurogenic impotence (erectile dysfunction due to a neurological disease). This reflex response is also referred as Osinski reflex which involves the bulbocavernosus muscle (also known as bulbospongiosus muscle). This also refers to the contraction of the anal sphincter in response to stimulation. The trigone is a part of the stimulation which is the anatomical triangular region formed by the ureteral and urethral orifices of the urinary bladder.

This is said to be performed in order to assess a person’s spinal cord integrity which basically reflects the functioning of our sacral sensory and motor fibers. Specifically, this will test the integrity of the sacral spinal roots; S2, S3 and S4.

The basic aim of this BCR is to verify the presence of spinal cord injury and shock. In medical research progress, there have been a number of grading systems for cord injury. The Frankel Classification can help us understand the extent of spinal cord injuries through their grading system:

  • Grade A: This would present the worst state of spinal cord injury with the complete absence of motor and sensory functions.
  • Grade B: There may be absence of motor function; sensory function is still intact.
  • Grade C: There is some motor function present (2/5 or 3/5) but not useful. Sensation is present.
  • Grade D: Motor function is present and fortunately about (4/5) useful with complete sensory function.
  • Grade E: Intact motor and sensory function

How to check for Bulbocavernosus?

There are certain techniques in stimulating the bulbocavernosus reflex. The bulbocavernosus reflex test involves stimulating and squeezing the penis of a man or by simply tugging or tapping his Foley catheter if present. A gloved finger shall be inserted in the rectum while the stimulation is performed to check for presence of the reflex.

Another method in testing is through an electrophysiological technique. This involves stimulation of the penis (some cases for vulva or clitoris) with recordings done from the anal sphincter. There shall be application of ring electrodes on the penis (if the case presents) and electrical stimuli are applied. Responses are acquired from needle electrodes fixed in the perineum between the penis and anus. The said average response from premade 50 – 100 stimuli is biphasic or composed of two phases. This method is essentially convenient for monitoring a patient’s sensory and motor functions.

Bulbocavernosus Reflex diagram

Picture : Bulbocavernosus Reflex diagram

Image source: health-7.com

Positive and Negative Reflex

When there is a cervical or thoracic cord injury, it is likely that absence of the bulbocavernosus reflex or negative reflex would be a result and would also signify presence of spinal shock and injury. The spinal shock may progress but then may resolve within 48 hours after injury. Return of the reflex would thankfully indicate end of spinal shock.

It is noted that patients with myelodysplasia (preleukemia disease involving the bone marrow) have distorted results. The results tend to be unstable and with manipulations. Complete deficiency of the distal motor and sensory functions or perirectal sensation, even though there is recovery of BCR, would lead to the conclusion of a complete spinal cord injury. A great value of neurological function may never return. When there is some motor and sensory function noted below the injury, this would indicate for an incomplete spinal cord injury.

In light to all of these, when there is return of the bulbocavernosus reflex or positive bulbocavernosus reflex, spinal shock is at end. It should be remembered that this test is not prognostic (basis for the outcome of an illness) for conus medullaris and cauda equina syndromes. These two syndromes arise from injuries of the distal end of spinal cord. The conus medullaris is anatomically located at the terminal end of the spinal cord while cauda equina is composed of the bundle of nerves of our spinal column. But when there is persistent loss of this reflex, conus medullaris syndrome is most likely the cause of the problem.

Treatment of this type of disease should be done by professionals only. If any of the symptoms are indicative, proceed to a doctor for advice.







    • It shouldn’t be, imho, don’t worry, I think in the situation where this might be required it would be least of our worries, as they’re basically checking if our nerves network is intact. It just might sound and feel weird to one who never read about it, as yeah, they’d basically have us relaxing to insert their finger or a thin electric probe in our anus, purposely lubricated of course and then shaking the penis glans to see our reflexive reaction of sphyncter contraction.
      I didn’t realize it happened everytime our penis head is touched and it’s basically linked to erection and ejaculation, because on top of the anus it contracts and shut down the bladder, which is also why we almost can’t pee during erection and what makes the penis do the jump when getting close to orgasm.

  1. It would be nice to have also the image of the vulva with an illustration of the kind of stimulation, the article is quite androcentric.


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