Sacral spinal nerve 4
The sacral spinal nerve 4 (S4) is a spinal nerve
Spinal nerve
The term spinal nerve generally refers to a mixed spinal nerve, which carries motor, sensory, and autonomic signals between the spinal cord and the body...

 of the sacral segment..

It originates from the spinal column from below the 4th body of the sacrum
In vertebrate anatomy the sacrum is a large, triangular bone at the base of the spine and at the upper and back part of the pelvic cavity, where it is inserted like a wedge between the two hip bones. Its upper part connects with the last lumbar vertebra, and bottom part with the coccyx...



S4 supplies many muscles, either directly or through nerves originating from S4. They are not innervated with S4 as single origin, but partly by S4 and partly by other spinal nerves. The muscles are:
  • iliococcygeus
    Iliococcygeus muscle
    The Iliococcygeus arises from the inner side of the ischium and from the posterior part of the tendinous arch of the obturator fascia, and is attached to the coccyx and anococcygeal raphé; it is usually thin, and may fail entirely, or be largely replaced by fibrous tissue...

  • puborectalis
    Puborectalis muscle
    The fibers which form a sling for the rectum are named the Puborectalis or Sphincter recti.They arise from the lower part of the pubic symphysis, and from the superior fascia of the urogenital diaphragm....

  • coccygeus
    Coccygeus muscle
    The Coccygeus is a muscle of the pelvic wall , located posterior to levator ani and anterior to the sacrospinous ligament....

  • Sphincter ani externus muscle
    Sphincter ani externus muscle
    The Sphincter ani externus is a flat plane of muscular fibers, elliptical in shape and intimately adherent to the integument surrounding the margin of the anus.-Anatomy:...

  • sphincter urethrae membranaceae
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