The anococcygeal nerve is a small sensory nerve that arises from the coccygeal plexus, formed by the anterior rami of the S4, S5, and coccygeal spinal nerves. It provides sensory innervation to the skin and tissues surrounding the coccyx and the anal region.
Location
The anococcygeal nerve originates from the coccygeal plexus, located in the pelvic region near the coccyx. It passes through the anococcygeal ligament, which is located between the coccyx and the anus. The nerve then extends to the skin over the coccyx and the lower anal area, where it provides cutaneous sensation. The nerve is situated in close proximity to the muscles of the pelvic floor.
Structure and Anatomy
The anococcygeal nerve is a small sensory nerve that originates from the coccygeal plexus and serves the skin and soft tissues around the coccyx and anus. Below is a detailed description of its anatomy, including its origin, course, branches, and anatomical relationships.
Origin
The anococcygeal nerve arises from the coccygeal plexus, which is formed by contributions from the S4, S5, and coccygeal spinal nerves. The coccygeal plexus is located near the lower end of the sacrum and the coccyx. The nerve fibers from these roots converge to form the small anococcygeal nerve.
Course
Pelvic Region
After its origin in the coccygeal plexus, the anococcygeal nerve travels anteriorly and inferiorly, passing through the anococcygeal ligament. This ligament is a fibrous structure that connects the coccyx to the anus.
Perineal Region
As it emerges from the coccygeal plexus, the nerve passes superficial to the coccygeus muscle and the levator ani muscle. These muscles form part of the pelvic floor, providing support to the pelvic organs. The nerve then continues its course toward the skin and tissues overlying the coccyx and lower anal region.
Anatomical Relationships
Pelvic Floor Muscles
- Coccygeus Muscle: The anococcygeal nerve lies in close proximity to the coccygeus muscle, a small muscle that forms part of the posterior pelvic floor. This muscle extends from the ischial spine to the lower sacrum and coccyx.
- Levator Ani Muscle: This large muscle, also part of the pelvic floor, supports pelvic organs and surrounds the anal region. The anococcygeal nerve courses near the levator ani muscle, which is responsible for maintaining continence and supporting the pelvic viscera.
Anococcygeal Ligament
The anococcygeal nerve passes through the anococcygeal ligament, which is a key anatomical landmark. This ligament is a connective tissue structure extending between the tip of the coccyx and the posterior wall of the anus, providing attachment for the coccygeus and levator ani muscles. The nerve emerges from the coccygeal plexus and travels through this ligament before branching into the skin of the coccygeal and anal regions.
Branches
The anococcygeal nerve gives off small sensory branches that supply the overlying skin and tissues around the coccyx and anus. These branches extend superficially over the lower back near the coccyx and anal area, providing innervation to the soft tissues and skin.
Anatomical Landmarks
- Coccyx: The anococcygeal nerve provides sensory innervation to the skin overlying the coccyx, the small, triangular bony structure at the base of the vertebral column.
- Anal Region: The nerve also supplies the skin and subcutaneous tissue in the area between the coccyx and the anus.
Variations in Anatomy
The course and distribution of the anococcygeal nerve can vary slightly among individuals, but it generally remains confined to the region of the coccyx and lower anal area. In some cases, there may be slight variations in the size or number of sensory branches arising from the nerve.
Termination
The anococcygeal nerve terminates by distributing its sensory branches to the skin and soft tissues over the coccyx and the anal region. Its fibers innervate the superficial tissues, allowing for sensation in the lower part of the coccyx and around the anus.
Function
The anococcygeal nerve is a small, primarily sensory nerve. Its primary function is to provide sensory innervation to the skin and superficial tissues around the coccyx and the lower part of the anal region. While it does not play a direct role in motor function, its sensory role is crucial for conveying signals related to sensation in this region. Below is a detailed description of its function.
Sensory Functions
The anococcygeal nerve’s primary role is to transmit sensory information from the coccyx and anal region to the central nervous system. The nerve provides sensory input related to touch, temperature, pain, and other stimuli in the lower back and perianal area.
Sensation of the Coccygeal Area
- The anococcygeal nerve supplies the skin and superficial tissues over the coccyx, which is the small, triangular bone located at the base of the spine. This area is particularly sensitive to touch and pressure due to its location near the bony coccyx.
- The nerve detects sensations such as pressure, touch, pain, and temperature in this region and relays that information to the brain. This is important for the perception of discomfort or injury in the coccygeal area, which can occur during prolonged sitting or trauma to the base of the spine.
Sensation of the Perianal Region
- In addition to the coccygeal area, the anococcygeal nerve provides sensory innervation to the skin and soft tissues of the lower anal region, which is the area between the anus and the coccyx.
- This nerve helps detect sensory stimuli such as touch and irritation in the lower anal area, contributing to overall awareness of sensation in the perineal region. It plays a role in detecting irritation, minor injuries, or discomfort that may occur in the anal region, which is crucial for maintaining skin integrity and responding to discomfort.
Pain Perception
The anococcygeal nerve plays a role in transmitting pain signals from the coccygeal and perianal regions. Pain in these areas may occur due to trauma, pressure, or inflammation, and the anococcygeal nerve is responsible for relaying this information to the brain.
Coccygeal Pain (Coccydynia)
Pain originating in the coccyx, known as coccydynia, may be caused by prolonged sitting, injury, or irritation of the tissues surrounding the coccyx. The anococcygeal nerve transmits the pain signals associated with this condition.
Perianal Pain
The anococcygeal nerve also conveys pain from the perianal region, which can be important in conditions involving irritation or minor trauma to the skin and soft tissues around the anus.
Limited Role in Reflexes
While the anococcygeal nerve primarily carries sensory fibers, it may have a minor role in transmitting sensory information related to reflexes in the lower pelvic region. For example, stimulation of the perianal skin may trigger responses that involve the pelvic floor muscles, although this is more directly related to other nerves in the region, such as the pudendal nerve.
No Motor Function
The anococcygeal nerve does not have a motor function. It is purely a sensory nerve, and it does not control any muscles or contribute to the movement of tissues in the coccygeal or perianal regions.
Clinical Significance
The anococcygeal nerve plays a role in conditions affecting the coccyx and perianal region, primarily related to pain perception and sensory disturbances.
Coccydynia (Tailbone Pain)
One of the most common conditions involving the anococcygeal nerve is coccydynia, which is characterized by pain in the coccyx area. This pain can be caused by trauma, prolonged sitting, or childbirth. The anococcygeal nerve transmits pain signals from the coccygeal region, making it a key structure in the sensation of tailbone pain.
Perianal Pain and Discomfort
Irritation or minor trauma to the skin in the perianal region, such as from prolonged sitting or pressure, can involve the anococcygeal nerve. Patients may experience discomfort or a burning sensation in the lower anal area, which is mediated by the nerve’s sensory fibers.
Nerve Entrapment
Although rare, nerve entrapment of the anococcygeal nerve may occur due to scarring or trauma in the lower pelvic region, leading to chronic pain in the coccygeal or perianal areas.
