A 24 years old female examined by an obstetrician in delivery room. Starting intravaginally, he injects lidocaine near the tip of the ischial spine. The nerve that is blocked by the drug is

Answer: (b) Pudendal nerve.* The ischium has a body and ramus (L. branch).* The body of the ischium helps form the acetabulum and the ramus of the ischium forms part of the obturator foramen.* The large postero-inferior protuberance of the ischium is the ischial tuberosity.* The small pointed posteromedial projection near the junction of the ramus and body is the ischial spine.* The concavity between the ischial spine and the ischial tuberosity is the lesser sciatic notch.* The larger concavity, the greater sciatic notch, is superior to the ischial spine and is formed in part by the ilium.* The pudendal nerve is the main nerve of the perineum and the chief sensory nerve of the external genitalia.* Accompanied by the internal pudendal artery, it leaves the pelvis through the greater sciatic foramen between the piriformis and coccygeus muscles.* It then hooks around the ischial spine and sacrospinous ligament and enters the perineum through the lesser sciatic foramen.Pudendal and llio-inguinal Nerve Blocks* To relieve perineal pain during childbirth, pudendal nerve block anesthesia may be performed by injecting a local anesthetic agent into the tissues surrounding the pudendal nerve.* The injection is made where the pudendal nerve crosses the lateral aspect of the sacrospinous ligament, near its attachment to the ischial spine.* The needle may be passed through the overlying skin or, more commonly perhaps, through the vagina parallel to the palpating finger.* Because the fetus's head is usually stationed within the lesser pelvis at this stage, it is important that the physician's finger is always positioned between the needle tip and the baby's head during the procedure.