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Root of penis
Root of penis
Root of penis
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Root of penis
Structure of the human penis. Root of the penis in 11; 4 corpus cavernosum, 5 corpus spongiosum, 6 scrotum, 7 crus, 8 bulb
Details
SystemGenitourinary
ArteryDorsal artery, bulbourethral artery, deep artery,
VeinDorsal veins, internal pudendal veins
NerveDorsal nerve, perineal nerves
Identifiers
Latinradix penis
TA98A09.4.01.002
TA23663
FMA19611
Anatomical terminology

In human male anatomy, the radix (/reɪ.dɪks/)[1] or root of the penis is the internal and most proximal portion of the human penis that lies in the perineum. Unlike the pendulous body of the penis, which is suspended from the pubic symphysis, the root is attached to the pubic arch of the pelvis and is not visible externally. It is triradiate in form, consisting of three masses of erectile tissue; the two diverging crura, one on either side, and the median bulb of the penis or urethral bulb.[2][3] Approximately one third to one half of the penis is embedded in the pelvis and can be felt through the scrotum and in the perineum.[4]

Structure

[edit]

The root of the penis begins directly below the bulbourethral glands, or Cowper glands, and consists of three long masses of tissue; the bulb and the crura. The bulb of the penis is an enlarged mass of erectile tissue that is located in the midline of the root and is traversed by the male urethra. It continues as a long cylindrical body on the ventral aspect of the shaft called corpus spongiosum.[5] The left and right crura are located laterally on the two sides of the bulb and are attached to the ischiopubic arch. They continue into the dorsal aspect of the shaft forming the two corpora cavernosa that are separated by the septum of the penis.[5] During arousal, the root and the corpora cavernosa engorge with blood and become rigid (erection). Meanwhile, the corpus spongiosum remains pliable making the urethra a viable channel for semen during ejaculation.[6]

Muscles

[edit]

There are four muscles associated with the root of the penis; a pair of ischiocavernosus and a pair of bulbospondiosus muscles.[5] Each crus is covered by the ischiocavernosus muscle which helps maintain an erection by contracting to force blood from the crura into the corpora cavernosa. The bulb is surrounded by the bulbospongiosus muscle which contracts to help empty the urethra of any residual semen and urine.[2] It also helps maintain the erection by increasing the pressure in the bulb. During orgasm, the muscles surrounding the root contract involuntarily pushing the semen towards the urinary meatus.

Fascia

[edit]

Each erectile tissue has fascial coverings, or bands of connective tissue, which surround and support them.[2] The root of the penis lies in the perineum between the perineal membrane, or inferior fascia of the urogenital diaphragm, and the fascia of Colles, the deeper layer of the superficial perineal fascia.

Ligaments

[edit]

In addition to being attached to the fasciæ and the pubic ramus, the root is bound to the front of the pubic symphysis by the fundiform and suspensory ligaments.[5]

  • The fundiform ligament springs from the front of the sheath of the rectus abdominis and the linea alba; it splits into two fasciculi which encircle the root of the penis.
  • The upper fibers of the suspensory ligament pass downward from the lower end of the linea alba, and the lower fibers from the pubic symphysis; together they form a strong fibrous band, which extends to the upper surface of the root, where it blends with the fascial sheath of the organ.

Images

[edit]
  • Root of the penis
    Root of the penis
  • Lateral cross-section of the male pelvis and its contents.
    Lateral cross-section of the male pelvis and its contents.

See also

[edit]

References

[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

Root of penis

View on Grokipedia
from Grokipedia
The root of the penis is the proximal, attached portion of the male genitalia that anchors the organ to the and perineal structures, consisting of two crura and a single formed from . The crura, which are the posterior extensions of the corpora cavernosa, attach separately to the undersurface of the ischiopubic rami, while the represents the proximal expansion of the corpus spongiosum surrounding the . These components are encased by the tunica albuginea, a fibrous sheath, and enveloped by the ischiocavernosus and bulbospongiosus muscles, which provide structural support and facilitate erectile function. During erection, the root's erectile tissues engorge with blood supplied by branches of the , with the surrounding muscles compressing veins to trap blood and maintain rigidity, preventing the from sinking into the under compressive forces. The specifically aids in expelling urethral contents, such as or , through rhythmic contractions, while the enhances blood flow to the distal corpora cavernosa. Innervation arises from the , contributing to sensory and motor functions essential for sexual response and . Clinically, the root's fixed position makes it susceptible to trauma, such as crush injuries from perineal impacts, which can affect erectile function due to its vascular and neural components. Understanding its anatomy is crucial for procedures involving the , , and reproductive health, as it forms the stable base connecting the visible shaft to the pelvic .

Overview

Definition and location

The root of the penis is the proximal, internal, and fixed portion of the organ, consisting of the bulb and crura that anchor it to the surrounding pelvic and perineal structures. It forms the foundational attachment point, distinguishing it from the more distal body and glans of the penis. This proximal segment is not externally visible and serves as the base for the erectile tissues that extend into the shaft. Anatomically, the root is situated within the superficial perineal pouch of the pelvic floor, specifically in the urogenital triangle of the perineum. It lies between the diverging ischiopubic rami, extending anteriorly to the body of the penis, with the perineal membrane forming its superior boundary. The structure is positioned inferior to the urogenital diaphragm, with the crura attaching laterally to the rami and the bulb centered midline. Embryologically, the root develops from the , an early ambisexual structure that emerges around the fifth week of near the cloacal . Under influence, the tubercle elongates into the , with the proximal portions forming through fusion of urethral folds and differentiation of mesenchymal tissues into the and crura, while the cloacal partitions to contribute to the and external genitalia.

Relations to surrounding structures

The root of the penis is situated within the urogenital triangle of the perineum, integrating closely with the pelvic floor structures to provide stability and support. Its superior boundary is formed by the perineal membrane, also known as the urogenital diaphragm, which serves as the roof of the superficial perineal pouch and separates the root from deeper pelvic contents. Inferiorly, the root relates to the perineal body—a fibromuscular mass at the center of the —and the superficial perineal , which bounds the structure below and facilitates continuity with the surrounding soft tissues. Laterally, the crura of the root attach firmly to the ischiopubic rami of the , anchoring the structure to the bony framework of the . Posteriorly, the bulb of the root lies in close proximity to the and , with the perineal body acting as a key intermediary that connects these elements and maintains separation between the urogenital and anal regions. Anteriorly, the root transitions smoothly into the at the penoscrotal junction, where the erectile tissues like the crura and converge to form the pendulous portion. The root occupies the , bounded superiorly by the and inferiorly by the superficial perineal fascia, while also interfacing with the adjacent through fascial layers that compartmentalize the perineal spaces. This positioning ensures the root's integration into the , contributing to overall structural integrity without direct involvement in adjacent visceral functions.

Anatomy

Erectile tissues

The erectile tissues of the root of the comprise the two crura and the , which form the foundational structures for penile rigidity. These components are extensions of the corpora cavernosa and corpus spongiosum, respectively, and are embedded within the to anchor the . The two crura represent paired extensions of the corpora cavernosa, diverging proximally and attaching laterally to the ischiopubic rami via the crus penis. Each crus is a cylindrical mass of that contributes to the dorsal aspect of the penile shaft distally. The crura are separated by an incomplete fibrous septum, known as the septum of the penis or pectiniform septum, which provides structural support and allows limited communication between the cavernous spaces. The bulb of the penis is the proximal expansion of the corpus spongiosum, located in the midline between the crura and traversed by the . It attaches inferiorly to the , facilitating its integration into the . Unlike the crura, the bulb has a more spongy architecture to accommodate the while supporting erectile function. These erectile tissues are composed of cavernous tissue featuring a network of trabeculae—fibromuscular partitions of and —that enclose irregular vascular spaces lined by . The entire structure is enveloped by the tunica albuginea, a dense fibrous sheath approximately 1 mm thick that reinforces the corpora and maintains their shape. The crura are briefly covered by the ischiocavernosus muscles for additional support. Histologically, the cavernous tissue contains sinusoidal spaces, which are dilated, endothelium-lined channels capable of expanding to accommodate blood inflow, thereby enabling engorgement and . These sinuses are supported by the trabecular framework, ensuring both flexibility in the flaccid state and rigidity when filled.

Muscles

The muscles associated with the root of the penis are primarily the paired ischiocavernosus muscles and the midline , which provide structural support and contribute to erectile and expulsive functions. These muscles are located in the , bounded superiorly by the and inferiorly by the deep perineal fascia, where they overlie the erectile tissues of the penile root. The ischiocavernosus muscles are paired skeletal muscles that originate from the medial surface of the and the ramus of the , extending forward to insert along the undersurface of the crura of the . Their contraction compresses the crura, thereby restricting venous outflow and promoting rigidity during by forcing blood distally into the corpora cavernosa. The , also known as the bulbocavernosus muscle, is a single midline muscle that originates from the perineal body and the median raphe overlying the of the . It encircles the and the proximal corpus spongiosum, with its fibers inserting into the , the dorsal fascia of the , and along the median raphe. This muscle aids in the expulsion of urine from the after micturition and during by compressing the and propelling contents forward. Anatomical variations in these muscles include occasional accessory slips or asymmetries, particularly in the bulbospongiosus, which may subdivide into ventral and dorsal portions with variable connections to adjacent structures such as the . The ventral portion of the bulbospongiosus often forms a morphological unity with the ischiocavernosus, while the dorsal origin exhibits up to five distinct variants in its relation to surrounding tissues.

Fascia and ligaments

The root of the penis is enveloped by several layers of and supported by ligaments that provide structural integrity and anchorage to the surrounding pelvic structures. These fibrous tissues extend from the penile shaft into the perineal region, forming distinct compartments that maintain the position of the erectile components during various physiological states. , also known as the deep fascia of the penis, represents a continuation of the deep perineal fascia and serves as a strong, membranous layer immediately superficial to the tunica albuginea of the erectile tissues. In the root, it envelops the crura of the corpora cavernosa and the bulb of the corpus spongiosum in separate compartments, extending proximally to attach to the and the ischiopubic rami. This fascial layer fuses distally with the base of the at the coronal sulcus, ensuring the erectile tissues remain firmly encased and supported. The superficial perineal fascia, continuous with Colles' fascia, forms the outermost fibrous layer in the perineal region and attaches anteriorly to the membranous layer of the superficial abdominal fascia (Scarpa's fascia). It blends with the dartos fascia of the penile skin and scrotum, extending posteriorly to fuse with the posterior border of the perineal membrane, thereby delineating the superficial perineal pouch. This attachment prevents direct continuity with deeper pelvic spaces, contributing to the isolation of superficial perineal contents. The suspensory ligament of the penis arises as a distal extension of , consisting of collagenous and elastic fibers that anchor the root to the . It connects the deep aspects of the corpora cavernosa to the anterior pubic , providing stabilization and limiting excessive mobility of the penile base. The , a superficial fibrous band derived from the linea alba of the , descends as a sling-like structure that partially encircles the penile shaft before attaching to the superficial near the . This ligament blends with the , offering additional elastic support to the penile skin and root without direct attachment to the erectile tissues. These fascial layers and ligaments play a critical role in compartmentalization, restricting the spread of pathological processes such as hematomas and infections within the . confines extravasated blood from penile fractures to the shaft if intact, preventing extension into the perineal or scrotal regions, while its rupture allows wider dissemination. Similarly, limits the posterior spread of superficial infections, such as in , by adhering to the , thereby isolating the superficial perineal space from the ischiorectal fossa and anal region. The ligaments further enhance this by maintaining structural boundaries that support compartmental separation during trauma or inflammation.

Vascular and nervous supply

Blood supply

The blood supply to the root of the penis, comprising the two crura and the , is primarily derived from branches of the , a terminal branch of the anterior division of the . The artery to the arises from the within the perineal pouch and supplies the of the corpus spongiosum, the proximal , and the bulbourethral glands. The deep arteries of the , also originating from the , course along the dorsomedial aspect of each crus before penetrating the corpora cavernosa to provide to the of the crura. Venous drainage from the root follows a parallel but distinct pathway to maintain efficient outflow. The crural veins emerge from the dorsolateral surface of each crus and converge to drain directly into the internal pudendal vein. The bulbar veins collect blood from the and empty into the , facilitating coordinated drainage with adjacent pelvic structures. Anastomotic connections enhance the vascular network's resilience, particularly between the penile veins and the prostatic via the bulbar veins, which supports integrated erectile function across the . Additionally, the deep dorsal vein of the penis links to the internal iliac veins through the puboprostatic ligament space, providing alternative drainage routes. Lymphatic drainage from the deeper structures of the root, including the crura and , primarily follows the vascular pathways to the internal iliac lymph nodes, ensuring efficient clearance from the proximal erectile tissues and proximal .

Innervation

The innervation of the root of the penis encompasses both somatic and autonomic components, primarily derived from the sacral spinal segments S2-S4. The , originating from the ventral rami of S2-S4, provides the main somatic motor and sensory supply to this region. Motor innervation to the root's associated muscles is supplied by the perineal branch of the , which innervates the ischiocavernosus muscles (enveloping the crura) and the (surrounding the bulb of the ). These motor fibers facilitate contraction of the perineal musculature, with the pudendal nerve's deep branch specifically targeting these striated muscles. Sensory innervation arises predominantly from the 's terminal branches. The , a continuation of the , provides sensory fibers to the skin covering the penile shaft and extends to the erectile tissues, including aspects of the root's crura and bulb. Additionally, the perineal nerves (including posterior scrotal branches) supply sensory innervation to the perineal skin overlying the root. The overall dermatomal distribution for these sensory inputs corresponds to S2-S4 segments. Autonomic innervation is mediated by the , which originate from the inferior hypogastric (pelvic) and carry parasympathetic fibers to the erectile tissues of the root. These nerves travel alongside the penile arteries to innervate the of the corpora cavernosa and spongiosum, primarily facilitating during . Sympathetic fibers from the same contribute to detumescence but are less dominant in the root's neural control.

Function

Role in erection

The root of the penis contributes to erection primarily through the engorgement of its erectile components, the paired crura of the corpora cavernosa and the central bulb of the corpus spongiosum. During , increased arterial inflow from the branches fills the vascular sinuses within these structures, causing them to expand and elongate. This process is initiated by parasympathetic activation, leading to relaxation in the cavernosal arteries and trabeculae. Central to this engorgement is -mediated in the sinusoidal spaces. , synthesized by neuronal and endothelial synthases in response to neural signals, diffuses into cells, activating to produce , which promotes relaxation and allows blood to accumulate under pressure. As the sinuses fill, intracavernosal pressure rises to approximately 100 mmHg in the crura, compressing subtunical veins against the tunica albuginea and restricting outflow to sustain . The experiences lower pressure, about one-third that of the crura, but still expands to support overall penile rigidity. Muscular contractions further enhance this mechanism during the rigid-erection phase. The ischiocavernosus muscles, which encircle the crura, contract rhythmically to compress these structures, propelling distally into the penile shaft and elevating intracavernosal to suprasystolic levels (several hundred mmHg), thereby rigidifying the corpora cavernosa. Similarly, the contracts around the bulb, forcing additional into the corpus spongiosum while aiding venous occlusion to prevent detumescence. The root's anchorage to the ischiopubic rami via the crura and provides biomechanical stability, anchoring the to the perineum and preventing axial buckling or collapse under thrust during full . This fixed proximal attachment, combined with distal engorgement, ensures the maintains a stable and structural integrity essential for intercourse.

Role in ejaculation and

The root of the penis, encompassing the bulb of the corpus spongiosum and the surrounding , is integral to the expulsion phase of . During this phase, rhythmic contractions of the compress the bulb, propelling through the bulbar urethra toward the external . These contractions occur at intervals of approximately 0.8 seconds, ensuring efficient seminal expulsion. The process is coordinated by -mediated spinal reflexes, which integrate sensory input from the penile skin and to trigger the expulsion following the emission phase, where is deposited into the . The provides somatic efferents to the bulbospongiosus, enabling the forceful, synchronized muscle activity essential for complete evacuation. In urination, the bulb serves as a compliant reservoir within the bulbar urethra, accommodating urine volume as it transitions from the membranous urethra, while relaxation of the bulbospongiosus muscle permits unimpeded flow. Post-voiding, the muscle contracts to expel any residual urine from the bulbar segment, preventing dribbling. The erectile tissue of the bulb maintains urethral patency during this flow. Pathologically, spasms or hypertonicity of the in the penile root can lead to by constricting the and disrupting coordinated relaxation during voiding. This dysfunction often manifests as painful or hesitant due to incomplete urethral emptying.

Clinical significance

Associated disorders

The root of the penis, comprising the crura and bulb, is susceptible to several pathological conditions that can impair its structural integrity and function. , characterized by fibrous plaques in the tunica albuginea of the corpora cavernosa, primarily affects the penile shaft but can involve proximal portions, potentially impacting the crura and leading to penile curvature, pain, and potential due to restricted expansion during . These plaques result from chronic inflammation and . Bulbar urethritis involves of the urethral bulb and surrounding spongiosum tissue, which can progress to fibrotic strictures narrowing the urethral lumen and obstructing flow. This condition arises from infectious, traumatic, or idiopathic etiologies, with symptoms including , recurrent infections, and . In severe cases, untreated leads to permanent scarring in the bulbar region, complicating voiding and increasing risks of proximal urinary tract dilation. Perineal trauma, commonly from injuries such as falls onto blunt objects, directly impacts the root of the penis by compressing the crura and against the pubic , resulting in , laceration, or vascular compromise that impairs erectile function. Such injuries often cause immediate swelling, ecchymosis, and pain in the , with long-term sequelae including of the erectile tissues and reduced rigidity due to disrupted blood flow. Congenital anomalies affecting the root include bulbar , where the urethral opens abnormally along the ventral aspect of the bulbar , often accompanied by and incomplete development. This malformation stems from disrupted embryologic fusion of the urethral folds, leading to symptoms such as redirected urinary stream, , and psychosocial concerns during development. Certain variants of involve veno-occlusive dysfunction at the crural level, characterized by inadequate compression of the crural veins during , allowing venous leakage that prevents sufficient corporal engorgement. These issues may arise from vascular supply disruptions, such as endothelial damage or fibrotic changes in the crural tunica, contributing to failure of the normal veno-occlusive mechanism.

Surgical and diagnostic considerations

(MRI) is a valuable tool for evaluating trauma to the root of the penis, particularly in cases of involving the crura or , as it provides detailed visualization of tunica albuginea tears and associated hematomas at the penile base. , especially color Doppler, assesses vascular patency in the crura by measuring peak systolic velocity and end-diastolic flow in the cavernosal arteries, aiding in the diagnosis of vascular insufficiency or high-flow . Surgical access to the often involves a perineal incision for procedures like bulbar , where a midline incision from the perineoscrotal junction exposes the bulbar and surrounding structures without transecting the corpora. This approach is indicated for conditions such as bulbar strictures. In penile implantation, the proximal cylinders are anchored to the crura or inferior pubic rami to ensure stability and prevent migration, typically via a penoscrotal incision that allows dilation of the corpora cavernosa extending to the . Suspensory release, combined with V-Y plasty, is a common procedure for penile lengthening, dividing the fundiform and suspensory ligaments to mobilize the penile shaft while preserving neurovascular integrity. Diagnostic evaluation of veno-occlusive dysfunction at the root level includes dynamic infusion cavernosometry, which measures maintenance flow rates and intracavernosal pressure to confirm corporal incompetence. Postoperative complications such as fascial hematomas can occur following root-related surgeries, including implantation, where they form within due to vascular injury and may require conservative management or evacuation if expansive.

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