The bulbocavernosus muscle, also known as the bulbospongiosus, is one of the superficial muscles of the perineum, the diamond-shaped area situated between the legs. It is a part of the pelvic floor musculature that plays a role in both urinary and sexual functions, contributing to the integrity of the pelvic region.
Anatomical Structure and Location
The bulbocavernosus muscle is a paired structure, meaning it consists of two symmetrical halves, located in the superficial perineal space. It originates from the central tendinous point of the perineum, called the perineal body, a fibrous knot between the anus and the genitals. From this origin, the muscle fibers extend forward to wrap around erectile tissues, with distinct differences between sexes.
In males, the muscle fibers meet at the midline to form a raphe, completely encasing the bulb of the penis and the corpus spongiosum, which contains the urethra. The anterior fibers insert onto the dorsal fascia of the penis. In females, the two muscle halves are separated, running along the sides of the vaginal opening. These fibers insert into the root of the clitoris and the pubic arch, covering the vestibular bulbs.
Essential Functions in Males and Females
The primary role of the bulbocavernosus muscle is to contract and compress the erectile and urinary structures it surrounds. In males, its function is associated with expulsive actions during urination and ejaculation. Rhythmic contractions of this muscle expel the final drops of urine from the urethra after voiding.
During sexual function, the muscle is considered the “muscle of ejaculation” because its powerful, rhythmic contractions propel semen through the urethra. It also contributes to maintaining the rigidity of an erection by compressing the deep dorsal vein of the penis. This compression helps trap blood within the erectile tissues, increasing pressure within the corpus spongiosum and further supporting the firmness of the erection.
In females, the muscle’s compression aids in constricting the vaginal opening and contributes to sexual response. It assists in clitoral erection by compressing the vestibular bulb and the dorsal vein of the clitoris, enhancing blood flow. The bulbocavernosus muscle is also an involuntary contributor to the muscular contractions experienced during orgasm. Its position around the vaginal opening helps support pelvic stability and pelvic floor function.
The Diagnostic Bulbocavernosus Reflex
Beyond its physiological functions, the bulbocavernosus muscle is involved in the Bulbocavernosus Reflex (BCR). This polysynaptic spinal reflex is used by clinicians to test the integrity of the sacral spinal cord segments. The test monitors for a reflex contraction of the bulbocavernosus muscle and the external anal sphincter.
The contraction is elicited by a sensory stimulus, such as squeezing the glans penis or the clitoris, or by tugging on an indwelling urinary catheter. This involuntary response confirms the functionality of the reflex arc, which is mediated by the Pudendal nerve and involves the S2 to S4 segments of the spinal cord. The presence or absence of the BCR is informative in the context of spinal cord injuries.
The BCR is often one of the first reflexes to return after spinal cord trauma, indicating the end of spinal shock. Its status helps physicians distinguish between different types of neurological lesions, such as those affecting the upper versus the lower motor neurons. The integrity of this reflex arc provides information regarding sacral nerve damage that may be causing conditions like urinary retention or sexual dysfunction.
Strengthening for Pelvic Health
The bulbocavernosus muscle can be strengthened through targeted exercise, commonly known as Kegels. These exercises involve intentionally contracting and relaxing the muscles that control the flow of urine. One simple way to identify this muscle is by attempting to stop the stream of urine mid-flow.
Weakness in this muscle can lead to several health issues, including post-void dribbling in men and urinary or fecal incontinence in both sexes. For men, a weak muscle can negatively affect sexual health, potentially resulting in erectile dysfunction and reduced ejaculatory force. Strengthening the muscle improves continence and enhances sexual function by increasing blood flow support and improving ejaculatory control.
To perform a basic strengthening exercise, squeeze the identified pelvic floor muscles, hold the contraction for a few seconds, and then fully relax. Performing these short and long holds multiple times a day helps build endurance and tone. Consistent practice can improve the ability to sustain an erection, increase the sensation of orgasm, and provide better support for the pelvic organs.