What Is the Penis Muscle Called? Names and Functions

There is no single “penis muscle.” The penis contains smooth muscle tissue inside its shaft and is acted on by two named skeletal muscles at its base: the ischiocavernosus muscle and the bulbospongiosus muscle. These three muscle systems work together to make erection and ejaculation possible, though they differ in what they are made of, where they sit, and what they do. Understanding which muscles are involved, and how, clears up a lot of confusion about how erections actually work and why they sometimes don’t.

The Two Skeletal Muscles at the Base

The muscles most people mean when they ask about “the penis muscle” are the ischiocavernosus and the bulbospongiosus. Both are striated (voluntary) skeletal muscles anchored in the pelvic floor, and both wrap around the root of the penis where it attaches to the pelvis. You can’t see them from the outside, and most men never think about them unless a doctor or physical therapist brings them up.

The ischiocavernosus muscle runs along each side of the penis root, covering the crus (the internal leg) of each corpus cavernosum. Its main job during an erection is to compress the base of the erectile tissue hard enough to push internal blood pressure above the level of systemic blood pressure. A review across multiple mammalian species confirmed that the ischiocavernosus muscles create rigidity by producing these suprasystolic intracavernous pressures, which is what takes an erection from partial to fully rigid.¹ Without the ischiocavernosus contracting, the penis fills with blood but doesn’t reach full stiffness.

The bulbospongiosus muscle wraps around the bulb of the penis, which is the expanded base of the corpus spongiosum (the spongy tissue that surrounds the urethra and forms the glans). This muscle has a different primary role: it propels fluid through the urethra. During ejaculation, rhythmic contractions of the bulbospongiosus expel semen in pulsatile bursts. It also helps push out the last drops of urine after you finish urinating.² Surgeons who operate on the urethra in this area try to spare the bulbospongiosus when possible, because splitting it can lead to weaker ejaculation and post-void dribbling.³

Both of these muscles contract partly under voluntary control and partly as reflexes. You can consciously squeeze them (this is what happens during a Kegel exercise), but they also fire automatically during orgasm and during certain reflex arcs triggered by stimulation.

The Smooth Muscle Inside the Shaft

The other “muscle” people sometimes wonder about isn’t a named muscle at all. It’s the smooth muscle tissue woven throughout the interior of the penis, especially inside the two corpora cavernosa, which are the paired cylinders of erectile tissue running the length of the shaft. Unlike the ischiocavernosus and bulbospongiosus, this smooth muscle is involuntary. You can’t flex it on command any more than you can voluntarily control the smooth muscle in your blood vessels or intestines.

This corporal smooth muscle is the tissue that actually makes erection happen at the mechanical level. When you’re not aroused, the smooth muscle stays contracted, keeping the blood vessels inside the penis narrow and limiting blood flow. During arousal, nerve signals trigger the release of nitric oxide, a chemical messenger that relaxes the smooth muscle.⁴ Researchers demonstrated this connection directly by showing that compounds blocking nitric oxide production prevented the corpus cavernosum from relaxing, while compounds that released nitric oxide caused rapid and complete relaxation of the tissue.⁵

As the smooth muscle relaxes, the spongy sinusoidal spaces inside the corpora cavernosa expand and fill with blood. This is the hydraulic event that produces tumescence. The relationship between the skeletal muscles at the base and the smooth muscle inside the shaft is cooperative: the smooth muscle relaxes to let blood in, and the skeletal muscles contract to lock it there at high pressure. Cadaveric and histological studies have confirmed that the skeletal muscle at the base physically contains and supports the smooth muscle tissue, creating a structural framework that links the two systems.⁶

How the Tunica Albuginea Traps Blood

The smooth muscle doesn’t work alone. The corpora cavernosa are wrapped in a tough, fibrous sheath called the tunica albuginea. This layer is mostly collagen and is relatively rigid, which is the whole point. When the smooth muscle relaxes and the sinusoidal spaces engorge with blood, the expanding tissue presses the small veins that normally drain blood out of the penis flat against the inside of the tunica albuginea. This compression pinches off the outflow routes, trapping blood inside.⁷ Animal studies have confirmed this directly, showing that in the erect state the postcavernous venules are compressed between the cavernous sinuses and the tunica albuginea.⁸

When this veno-occlusive mechanism fails, blood flows into the penis normally but leaks back out before full rigidity is achieved. This condition, sometimes called venous leak, is one cause of erectile dysfunction and is related to changes in the tunica albuginea or loss of smooth muscle tissue rather than a problem with the skeletal muscles at the base.

What Happens to These Muscles with Age

One of the less-discussed reasons erectile function declines with age has nothing to do with arteries clogging or testosterone dropping. The smooth muscle cells inside the corpora cavernosa gradually degrade and disappear over time. Research suggests that when roughly 15% of these cells have been lost or become dysfunctional, the corporal tissue can no longer expand enough to compress the drainage veins against the tunica albuginea, and blood begins leaking out of the sinusoidal spaces into the systemic veins.⁹ This is a structural problem at the tissue level, distinct from arterial disease, though the two often occur together in older men.

The skeletal muscles at the base weaken with age too, as all skeletal muscles do, but their decline is potentially reversible through exercise in a way that smooth muscle loss currently isn’t. This distinction matters for understanding why pelvic floor exercises help some men and not others, a topic worth exploring on its own.

Pelvic Floor Training and Sexual Function

The ischiocavernosus and bulbospongiosus are part of the broader pelvic floor muscle group, and training them is what happens during male Kegel exercises or formal pelvic floor rehabilitation. A randomized controlled trial found that men with erectile dysfunction who performed pelvic floor exercises and biofeedback saw meaningful improvements: about 40% regained normal erectile function and another 35% improved, with only a quarter showing no benefit.¹⁰ A systematic review covering multiple trials confirmed that pelvic floor muscle training appears effective for both erectile dysfunction and premature ejaculation, though researchers have not settled on the best training protocol.¹¹

For premature ejaculation specifically, pelvic floor training targets the bulbospongiosus muscle’s role in the ejaculatory reflex. One study found that after training, over 80% of men with lifelong premature ejaculation gained control of their ejaculatory reflex, with the average time to ejaculation roughly tripling from baseline and remaining improved at follow-up months later.¹² A more recent comparative study showed improvements in both acquired and lifelong premature ejaculation after eight weeks of training, with gains in both contraction pressure and symptom scores.¹³

These exercises also have a role after prostate surgery. Men who undergo radical prostatectomy commonly experience urinary incontinence because the surgery disrupts the structures that help control urine flow. A systematic review and meta-analysis found that pelvic floor muscle training significantly improved stress urinary incontinence after prostatectomy.¹⁴ Research also suggests that starting pelvic floor exercises before surgery (prehabilitation) leads to faster recovery and less leakage compared to waiting until after the operation.¹⁵

When Kegel Exercises Can Make Things Worse

Not every pelvic floor problem calls for strengthening. Men with chronic pelvic pain syndrome often have pelvic floor muscles that are already overactive or chronically tense. For them, doing Kegels can actually increase pain and worsen symptoms. As one group of researchers put it, many patients have hypertonic musculature that requires relaxation rather than strengthening, and Kegel exercises can make things worse for some men with this condition.¹⁶ For these men, the right approach is learning to relax the pelvic floor muscles through stretching, manual therapy, and down-training rather than contracting them harder. This is a common and frustrating misconception: the generic advice to “do your Kegels” doesn’t apply to everyone, and for a subset of men it actively backfires.

Nearby Muscles People Confuse with Penile Muscles

A few other muscles in the region are sometimes lumped in with “penis muscles” but serve different purposes entirely.

The dartos muscle is a thin sheet of smooth muscle just beneath the skin of the scrotum. It’s responsible for the wrinkling and tightening of scrotal skin you notice when it’s cold.¹⁷ Its job is thermoregulation: by contracting, it pulls the testes closer to the body to keep them warm, and by relaxing, it lets them hang lower to cool off. Research has identified a specific cold-sensitive receptor channel involved in this process, linking the dartos muscle’s contractions directly to temperature sensing at the cellular level.¹⁸ A thin extension of dartos tissue also exists in the penile shaft skin, but it plays no role in erection or ejaculation. Problems with dartos nerve supply can affect testicular temperature regulation and potentially spermatogenesis.¹⁹

The cremaster muscle is a thin skeletal muscle that loops around each spermatic cord and testicle. It produces the “cremasteric reflex,” the familiar testicular retraction that happens when the inner thigh is stroked or during a cold plunge. The cremaster is important for testicular thermoregulation and certain sexual reflexes.²⁰ In some men, an overactive cremaster reflex causes bothersome testicular retraction. Studies have found that men with this problem have cremaster muscles roughly four times thicker than men without it.²¹ Neither the dartos nor the cremaster directly affects erection, but both are so close anatomically that they come up in nearly every discussion of male genital anatomy.

The Retractor Penis Muscle and Why Humans Don’t Have One

If you’ve ever seen anatomical diagrams of animal reproductive systems, you may have noticed a muscle called the retractor penis muscle. This smooth muscle runs along the underside of the penis in many mammals, including dogs, cattle, and horses, and its job is to pull the non-erect penis back into the prepuce (sheath) after mating. Humans don’t have a retractor penis muscle. Over evolutionary time, as the human penis lost the baculum (penis bone) that many other mammals still have, the retractor muscle was also lost. This is one of the reasons the human penis is structurally different from that of most other mammals: it relies entirely on hydraulic blood pressure rather than a combination of a bone, a retraction muscle, and blood pressure.

Stem Cell Research and Smooth Muscle Repair

Because so much of age-related and post-surgical erectile dysfunction traces back to the loss of corporal smooth muscle cells, researchers have been exploring whether stem cell therapies could regenerate that tissue. A systematic review and meta-analysis of animal studies found that stem cell therapy after cavernous nerve injury showed some promise for nerve regeneration but was less effective at restoring smooth muscle cells specifically.²² This remains an active area of research. The challenge is that smooth muscle recovery may require different approaches than nerve regeneration, and most current work is still in animal models. Human trials are underway at several centers, but no stem cell treatment for erectile dysfunction has received regulatory approval. If smooth muscle regeneration eventually proves feasible, it would address the root cause of veno-occlusive dysfunction in a way that current medications and pelvic floor exercises cannot.