SOMATIC NERVES (SACRAL PLEXUS)

1. SOMATIC NERVES(SACRAL PLEXUS) • It is situated on the posterolateral wall of the pelvic cavity, in front of the piriformis muscle.

2. RELATIONS • Anterior : • 1. Parietal pelvic fascia separating it from the internal iliac vessels. • 2. Rectum. • Posterior : • Piriformis muscle.

3. STRUCTURE • It is formed from the ventral rami of (S1- S4) and a contribution from the lumbosacral trunk.

4. LUMBOSACRAL TRUNK • It is formed of part of the ventral ramus of L4 and all of the ventral ramus of L5. • It descends vertically anterior to the sacroiliac joint.

5. BRANCHES OF S.P • (A) Passing through the greater sciatic foramen to supply the L.L: • 1. Sciatic nerve (L4-S3). • It is the largest nerve of the plexus and of the body. • It supplies all posterior muscles of back of thigh and leg and all muscles of the sole.

6. BRANCHES • 2. Superior gluteal nerve (to glutei medius & minimus and tensor fascia lata). • 3. Inferior gluteal nerve (to gluteus maximus). • 4. Nerve to obturatorinternus (and superior gemellus).

7. BRANCHES • 4. Nerve to quadratus femoris (and inferior gemellus). • 5. Posterior cutaneous nerve of the thigh: • It supplies the skin of the buttock and back of the thigh.

8. BRANCHES • (B) Branches to the pelvis and perineum:(muscles & viscera) • 1. Pudendal nerve(S2,3 &4) : • It enters the perineum through the lesser sciatic foramen.

9. BRANCHES • 2. Nerve to piriformis. • 3. Pelvic splanchnic nerves (S2,3 &4). • (c) Perforating cutaneous : to the skin of the lower medial part of the buttock.

10. OBTURATOR NERVE • It accompanies the lumbosacral trunk to enter the pelvis. • It runs on the lateral pelvic wall.

11. OBTURATOR NERVE • It lies in the angle between the external and internal iliac vessels. • At the obturator canal, it splits into anterior and posterior divisions that pass through the canal to enter the thigh. • It gives sensory supply to the parietal peritoneum.

12. AUTONOMIC SUPPLY (PELVIC SYMPATHETIC TRUNK) • It is the continuation of the abdominal trunk. • It is formed of (4- 5) ganglia. • It descends in front of the ala sacrum, medial to the lumbosacral trunk.

13. (PELVIC SYMPATHETIC TRUNK) • On the anterior surface of the sacrum, it is medial to the • anterior sacral foramina. • It is behind the rectum.

14. PELVIC SYMPATHETIC TRUNK • Inferiorly, the two trunks unite in front of the coccyx and form a single ganglion (ganglion impar).

15. BRANCHES • 1. Gray rami communicantes to the lumbar and sacral nerves. • 2. Fibers to hypogastricplexuses.

16. HYPOGASTRIC PLEXUSES (1) SUPERIOR • Site : in front of the promontry of the sacrum. • Structure : • 1. continuation of the aortic plexuses. • 2. from the 3rd and 4th lumbar ganglia.

17. SUPERIOR HYPOGASTRIC PLEXUS • Contained fibers: Postganglionic sympathetic, parasympathetic and visceral afferent. • Termination: • It divides into: • Right and Left hypogastric nerves.

18. (2) INFERIOR HYPOGASTRIC PLEXUS • Site : on each side of rectum, bladder and vagina. • Structure : • Right and left hypogastric nerves. • pelvic splanchnic nerves.

19. INFERIOR HYPOGASTRIC PLEXUS • Contained fibers : • Postganglionic sympathetic. • Pre and post ganglionic parasympathetic. • Visceral afferent. • Distribution : • To the pelvic viscera through small subsidary plexuses.

20. PELVIC SPLANCHNIC NERVES • It is the parasympathetic component of the pelvis. • It arises from (S2,3 &4). • The fibers synapse in the inferior hypogastric plexus or in the walls of the viscera. • Some fibers can ascend to the inferior mesenteric plexus and distribute among the branches of the inferior mesentericartery.

21. EXTERNAL ILIAC ARTERY • Origin : • One of terminal branches of the common iliac artery in front of the sacroiliac joint. • Course : • It descends along the medial border of posoas major. • It enters the thigh by passing deep to the inguinal ligament and becomes the femoral artery.

22. EXTERNAL ILIAC ARTERY • Branches (in the false pelvis) : • Inferior epigastric. • Deep circumflex iliac.

23. INTERNAL ILIAC ARTERY • Origin : • The other terminal branch of the common iliac artery. • Course : • It descends inferiorly over the pelvic inlet. • Termination : • At the upper border of the greater sciatic foramen, it divides into anterior and posterior divisions.

24. POSTERIOR DIVISION • It supplies : • Posterior abdominal wall, posterior pelvic wall and the gluteal region. • Branches : • (1) Iliolumbar artery: • It ascends behind the external iliac vessels, psoas and iliacus. • It divides into lumbar branch (it supplies the muscles of the posterior abdominal wall) and iliac branch for iliacus muscle and bone.

25. POSTERIOR DIVISION • (2) Lateral sacral arteries : • Usually two. • They descend in front of the sacral plexus. • They give branches that pass into the anterior sacral foramina to supply structures in the vertebral canal, muscles and skin.

26. POSTERIOR DIVISION • (3) Superior gluteal artery : • It leaves the pelvis through the greater sciatic foramen, above the piriformis. • It supplies the gluteal region.

27. ANTERIOR DIVISION • It supplies : • Pelvic viscera. • Perineum. • Gluteal region. • Adductor region of the thigh. • The fetus.

28. ANTERIOR DIVISION • (A) Visceral branches: • 1. Umbilical artery : • It gives the superiorvesicalartery (to the upper part of the urinary bladder) from its patent proximal part. • The distal fibrous part of the artery becomes the medial umbilical ligament.

29. ANTERIOR DIVISION • 2. Inferior vesical artery : • It supplies the base of the bladder. • In the male it supplies, the prostate and the seminal vesicles. • It gives the artery to the vas deferens.

30. ANTERIOR DIVISION • (3) Middle rectal artery : • It usually arises with the inferior vesical. • It supplies the muscle layer of the lower rectum . • It anastomoses with the superior and inferior rectal arteries.

31. ANTERIOR DIVISION • (4) Vaginal artery : • It replaces the inferior vesical artery in the female. • It supplies the base of the bladder and vagina.

32. ANTERIOR DIVISION • (5) Internal pudendal artery : • It is the main arterial supply to the perineum (skin & muscles) and the anal canal. • It leaves the pelvis through the lower part of the GSF below the piriformis. • It enters the perineum through the LSF.

33. ANTERIOR DIVISION • (6) Uterine artery : • It runs on the pelvic floor. • It crosses the ureter superiorly. • It passes between the layers of the broad ligament along the lateral margin of the uterus. • It anastomoses with the ovarian artery.

34. ANTERIOR DIVISION • (B) Parietal branches: • 1. Inferior gluteal : • It leaves the pelvis through the lower part of the GSF below piriformis. • It passes between the sacral nerves (S1- S2) or (S2- S3)

35. ANTERIOR DIVISION • 2. Obturator artery: • It accompanies the obturator nerve along the lateral pelvic wall. • It leaves the pelvis through the obturator canal.

36. OVARIAN ARTERY • It arises from the abdominal aorta. • Unlike the testicular artery, it enters the pelvis behind the peritoneum. • It enters the suspensory ligament of the ovary and passes into the broad ligament.

37. MEDIAN SACRAL ARTERY • It originates from the posterior surface of the aorta just superior to its bifurcation. • It descends in the midline, in front of the anterior surface of the sacrum and coccyx.

38. EXTERNAL ILIAC VEIN • It begins behind the inguinal ligament as a continuation of the femoral vein. • It ascends along the medial side of its corresponding artery. • It receives the inferior epigastric anddeep circumflex veins.

39. INTERNAL ILIAC VEIN • It has tributaries corresponding to the branches of the internal iliac artery. • It ascends in front of the sacroiliac joint. • It joins the external iliac vein to form the common iliac vein.

40. MEDIAN SACRAL VEIN • It accompanies its artery. • It terminates in the left common iliac vein.

41. LYMPH DRAINAGE • The lymph nodes and vessels are arranged in a chain along the main blood vessels. • They are named according to these vessels: Internal iliac, External iliac and Common iliac.

42. SACROILIAC JOINTS • They are strong synovial joints. • Articular surfaces : • Auricular surfaces of the sacrum and the iliac bones.

43. SACROILIAC JOINTS • Stability : • It depends on the strong ligaments : • 1. Posterior. • 2. interosseous sacroiliac ligaments. • The anterior ligament is thin.

44. SACROILIAC JOINTS • Function : • Transmitting the weight of the body from the vertebral column to the bony pelvis.

45. ROTATION OF THE SACRUM • The weight of the body tends to thrust the upper end of the sacrum downwards and rotates the lower end upwards.

46. ROTATION OF THE SACRUM • This is prevented by the following ligaments : • Sacrospinous. • Sacrotuberous. • Iliolumbar : • It is between the tip of the transverse process of L5 and the iliac crest.

47. SYMPHSIS PUBIS • It is a secondary cartilagenous joint. • The two pubic bones are covered by hyaline cartilage and connected together by a fibrocartilagenous disc. • The joint allows no movement.

48. SACROCOCCYGEAL JOINT • It is a cartilagenous joint between the bodies of the last sacral vertebrae and the 1st coccygeal vertebra. • It has a great amount of movement.