The perineal nerves are branches of the pudendal nerve, which arises from the sacral plexus (S2-S4). These nerves are primarily responsible for providing motor and sensory innervation to the perineum, the area between the anus and the genitals. The perineal nerves are divided into two main branches: the deep perineal nerve and the superficial perineal nerve.
Location
The perineal nerves originate from the pudendal nerve as it courses through the pudendal canal (Alcock’s canal), located in the pelvic region. These nerves travel through the ischiorectal fossa, a fat-filled space in the perineum, and extend toward the urogenital region, innervating structures in the perineum. The deep perineal nerve primarily innervates muscles of the pelvic floor, while the superficial branch provides sensory innervation to the skin of the perineum.
Structure and Anatomy
The perineal nerves are branches of the pudendal nerve and are primarily responsible for innervating the perineum, including its muscles and skin. The perineal nerves are divided into deep and superficial branches, each serving different anatomical structures in the perineum. Below is a detailed description of their anatomy, including their origin, course, branches, and relationships with surrounding structures.
Origin
The perineal nerves arise from the pudendal nerve, which originates from the sacral plexus (S2-S4). The pudendal nerve exits the pelvis through the greater sciatic foramen and re-enters through the lesser sciatic foramen, traveling through Alcock’s canal (pudendal canal), a fibrous tunnel formed by the fascia of the obturator internus muscle.
Course
Pelvic Region
After the pudendal nerve enters Alcock’s canal, the perineal nerves branch off within the ischiorectal fossa, a space located laterally to the anus and inferior to the pelvic floor. The perineal nerves course medially toward the perineum, passing beneath the levator ani muscles.
Perineum
Once they enter the perineum, the perineal nerves divide into deep and superficial branches, each of which follows a different path to innervate specific structures.
Branches
Deep Perineal Nerve
The deep perineal nerve provides motor innervation to the muscles of the urogenital diaphragm and the superficial perineal pouch. This branch travels through the deep perineal space and innervates several muscles associated with the pelvic floor, such as:
- Bulbospongiosus Muscle: This muscle surrounds the base of the penis in males or the vestibular bulbs in females.
- Ischiocavernosus Muscle: This muscle stabilizes the penis or clitoris during sexual arousal.
- Superficial Transverse Perineal Muscle: This muscle helps support the pelvic organs and is part of the superficial perineal pouch.
Superficial Perineal Nerve
The superficial perineal nerve provides sensory innervation to the skin of the perineum and external genitalia. It splits into smaller branches:
- Posterior Scrotal Nerves (in males) or Posterior Labial Nerves (in females): These branches provide sensory innervation to the scrotum in males and the labia majora in females.
- Cutaneous Branches: Smaller cutaneous branches innervate the skin of the perineum, transmitting sensory information from this region to the central nervous system.
Communicating Branches
The perineal nerves have communicating branches that connect with other nerves in the region, such as the inferior rectal nerve, which innervates the anal sphincter and surrounding structures. These communicating branches help integrate sensory and motor functions of the perineum.
Anatomical Relationships
Levator Ani Muscles
The perineal nerves run below the levator ani muscles, which are part of the pelvic diaphragm. These muscles support pelvic organs and control the release of urine and feces. The perineal nerves pass underneath this muscular layer as they move toward the perineum.
Ischiorectal Fossa
The perineal nerves course through the ischiorectal (ischioanal) fossa, a fat-filled space located between the pelvic diaphragm and the skin of the perineum. This space provides a passageway for the nerves and blood vessels that innervate the perineum.
Perineal Membrane
The perineal nerves also pass through or near the perineal membrane, a fibrous sheet that spans the urogenital triangle and provides structural support to the pelvic organs. The deep perineal nerve branches innervate muscles located on or near this membrane.
Distribution
In Males
In males, the perineal nerves provide sensory innervation to the scrotum, penis, and the skin of the perineum. The deep perineal nerve also innervates muscles that contribute to the erectile function of the penis, such as the bulbospongiosus and ischiocavernosus muscles.
In Females
In females, the perineal nerves provide sensory innervation to the labia majora, labia minora, and perineal skin. The deep perineal nerve innervates muscles associated with the erectile function of the clitoris, including the bulbospongiosus and ischiocavernosus muscles.
Anatomical Landmarks
- Ischial Tuberosities: The perineal nerves course near the ischial tuberosities, bony landmarks located on either side of the perineum. These landmarks serve as reference points for the location of the perineal nerves during clinical examinations.
- Urogenital Triangle: The perineal nerves are primarily located within the urogenital triangle, which is the anterior portion of the perineum. The deep and superficial branches of the perineal nerves provide motor and sensory innervation to the structures within this triangle.
Variations in Anatomy
The course and branching patterns of the perineal nerves can vary slightly among individuals. Some people may have additional or fewer branches, and the location of these nerves relative to pelvic structures may differ slightly.
Termination
The perineal nerves terminate in the sensory and motor structures of the perineum. The deep perineal nerve terminates in the muscles of the urogenital diaphragm, while the superficial perineal nerve terminates in the skin and superficial structures of the perineum and external genitalia.
Function
The perineal nerves are branches of the pudendal nerve and play a crucial role in the motor and sensory innervation of the perineum and external genitalia. These nerves are divided into deep and superficial branches, each responsible for different functions within the perineal region. Below is a detailed explanation of their motor and sensory functions.
Motor Functions
The deep perineal nerve provides motor innervation to the muscles located in the urogenital diaphragm and superficial perineal pouch. These muscles play key roles in supporting the pelvic organs, controlling urination, and contributing to sexual function.
Urogenital Diaphragm Muscles
The perineal nerves innervate muscles in the urogenital diaphragm, which provides structural support to the pelvic organs.
- Bulbospongiosus Muscle: This muscle is involved in functions related to sexual activity and urination. In males, it helps with the ejaculation process by compressing the urethra, and in both sexes, it helps expel the last drops of urine from the urethra after voiding.
- Ischiocavernosus Muscle: This muscle contributes to the erectile function of the penis in males and the clitoris in females. It helps maintain penile or clitoral erection by compressing the veins and restricting blood flow out of these structures during sexual arousal.
- Superficial Transverse Perineal Muscle: This muscle provides structural support to the pelvic organs and helps stabilize the perineal body, a fibromuscular mass that supports the pelvic floor. It also assists in supporting the external anal sphincter.
Muscles of the External Genitalia
The deep perineal nerve innervates the muscles responsible for the movement and support of the external genitalia. These muscles aid in sexual function and structural support:
External Urethral Sphincter: This muscle is innervated by the deep perineal nerve and controls voluntary urination by contracting and relaxing around the urethra. It plays an essential role in maintaining continence.
Sensory Functions
The superficial perineal nerve provides sensory innervation to the skin of the perineum and the external genitalia. Sensory input from these areas is crucial for various functions, including sexual sensation, awareness of touch, and detection of temperature or pain.
Sensory Supply to the Perineum
The superficial branches of the perineal nerve provide sensory innervation to the skin of the perineum, which is the area between the anus and the genitals. These nerves detect:
- Touch: The perineal nerves allow for the detection of light touch and pressure in the perineal region, which is important for normal sensory feedback during movement and in activities such as sitting.
- Temperature: The nerves transmit information about changes in temperature in the perineum, ensuring the body’s ability to detect heat or cold in this region.
- Pain: The perineal nerves relay pain signals, allowing for the detection of irritation, injury, or discomfort in the perineal region.
Sensory Supply to the External Genitalia
The perineal nerves, through their superficial branches, innervate the skin of the external genitalia, providing essential sensory input that contributes to sexual sensation.
- Posterior Scrotal Nerves (in males): These branches provide sensory innervation to the scrotum, allowing for the detection of touch, pressure, and temperature, which is important for normal sensation and sexual function.
- Posterior Labial Nerves (in females): These branches provide sensory innervation to the labia majora and labia minora, which are involved in sexual sensation. These nerves detect touch and pressure, playing a key role in sexual arousal and sensation.
Sexual Function
The perineal nerves are involved in various aspects of sexual function, especially through their sensory branches. In males, the perineal nerves contribute to the sensation of the penis and scrotum, while in females, they contribute to the sensation of the clitoris and labia. The motor branches of the perineal nerves innervate muscles that assist in erection, ejaculation, and orgasm by supporting the vascular and muscular mechanisms involved in these processes.
In Males
- The deep perineal nerve innervates the ischiocavernosus muscle, which helps maintain penile erection by compressing veins and limiting blood flow out of the penis.
- The bulbospongiosus muscle plays a role in ejaculation by helping to expel semen during orgasm.
In Females
- The perineal nerves provide sensation to the clitoris and labia, playing a key role in sexual arousal and orgasm. The ischiocavernosus muscle, innervated by the deep perineal nerve, supports clitoral erection.
Contributions to Continence
The deep perineal nerve also innervates muscles responsible for maintaining continence. The external urethral sphincter is controlled by this nerve, allowing for voluntary control over urination by contracting to close the urethra and relaxing to allow urination.
Clinical Significance
The perineal nerves are essential for motor and sensory functions in the perineum and external genitalia. Injury or dysfunction of these nerves can lead to significant clinical issues.
Perineal Nerve Injury
Injuries to the perineal nerves can result from pelvic trauma, childbirth, or surgery, leading to sensory loss or motor dysfunction in the perineal region. This may manifest as numbness, pain, or weakness in the pelvic floor muscles, affecting continence and sexual function.
Pelvic Floor Dysfunction
Damage to the motor branches of the perineal nerves can contribute to pelvic floor dysfunction, resulting in problems like urinary incontinence or fecal incontinence due to weakened control of the pelvic floor muscles and sphincters.
Chronic Perineal Pain
Compression or irritation of the perineal nerves, such as in pudendal neuralgia, can cause chronic perineal pain. This condition results in burning or aching pain in the perineum, affecting the quality of life, particularly during sitting or sexual activities.
Sexual Dysfunction
Injury to the perineal nerves can impair sensation in the external genitalia, potentially leading to sexual dysfunction in both men and women, including decreased sensation, difficulty achieving orgasm, or erectile dysfunction.
