Human Anatomy, Part 2 - K. A. Dyubenko, A. K. Kolomiysev, Yu. B. Chaykovsky 2008

Special Part
Peripheral nervous system, systema nervosum periphericum — General Overview
Spinal nerves — Lumbosacral plexus

It is divided into the Lumbar plexus, plexus lumbalis, and the Sacral Plexus, plexus sacralis, which are connected by the lumbosacral trunk, truncus lumbosacralis. The latter consists of a portion of the fibers from the anterior ramus of the fourth lumbar nerve and the anterior ramus of the fifth lumbar nerve.

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Fig. 197. Lumbar plexus, plexus lumbalis (sources of formation and its nerves)

Fig. 197-A. Lumbar plexus, plexus lumbalis

Lumbar plexus, plexus lumbalis [lumbaris] (LNA)

The lumbar plexus is formed by the anterior rami of the twelfth thoracic and the first through fourth lumbar nerves (Fig. 197). A small number of fibers passes to the lumbar plexus from the anterior ramus of the twelfth thoracic nerve, i.e., the subcostal nerve, while the greater part of the fibers originates from the anterior ramus of the fourth lumbar nerve (with a smaller part entering the COMPOSITION OF THE lumbosacral trunk).

The lumbar plexus is located posterior to the psoas major Muscle.

The plexus gives off the following branches (Fig. 197):

1. Iliohypogastric nerve, nervus iliohypogastricus (Th_XII-L_I), emerges from beneath the lateral border of the psoas major muscle onto the anterior surface of the quadratus lumborum muscle, and subsequently pierces the transversus abdominis muscle. It supplies motor branches to the latter and to the broad Abdominal Muscles. The iliohypogastric nerve also gives off a lateral cutaneous branch, ramus cutaneus lateralis, to the Skin of the greater trochanter region, and an anterior cutaneous branch, ramus cutaneus anterior, to the skin in the area of the superficial inguinal ring.

2. Ilioinguinal nerve, nervus ilioinguinalis (L_I), runs inferior to the previous nerve, enters the Inguinal Canal, and reaches its superficial ring. Along its course, it gives off branches to the Muscles of the anterolateral abdominal wall. Its terminal branches in males are the anterior scrotal nerves, nervi scrotales anteriores, and in females, the anterior labial nerves, nervi labiales anteriores, which innervate the skin of the external genitalia.

3. Genitofemoral nerve, nervus genitofemoralis (L_I-L_II), pierces the psoas major muscle and divides on its anterior surface into a genital branch, ramus genitalis, and a femoral branch, ramus femoralis. The former pierces the transversalis fascia, enters the inguinal canal, and innervates the structures of the Spermatic Cord and the coverings of the Testis in males, or the round ligament of the Uterus in females. The latter passes onto the thigh through the vascular lacuna (lateral to the femoral artery) and innervates the skin area inferior to the inguinal ligament.

4. Lateral femoral cutaneous nerve, nervus cutaneus femoris lateralis (L_II-L_III), emerges from beneath the lateral border of the psoas major muscle, crosses the iliacus muscle, and reaches the thigh through the muscular lacuna near the anterior superior iliac spine. Piercing the fascia lata, it becomes subcutaneous on the lateral surface of the thigh, which it innervates.

5. Femoral nerve, nervus femoralis (L_II-L_IV), is the thickest of the NERVES OF THE lumbar plexus (Fig. 197 A). Within the pelvis, it lies between the psoas major and iliacus muscles, to which it gives off branches. It passes onto the thigh through the muscular lacuna medial to the iliopsoas muscle. It divides into muscular branches, rami musculares, to the pectineus, sartorius, and quadriceps femoris muscles; anterior cutaneous branches, rami cutanei anteriores, to the skin of the anterior surface of the thigh; and the saphenous nerve, nervus saphenus. The latter runs together with the femoral artery through the adductor canal, then, accompanying the descending genicular artery, emerges through the anterior opening of the canal, passes beneath the sartorius muscle, and pierces the fascia at the level of the tibial tuberosity. In the leg, the nerve runs subcutaneously alongside the great saphenous vein, giving off medial sural cutaneous branches, rami cutanei cruris mediales, which innervate the skin of the anteromedial surface of the leg. The infrapatellar branch, ramus infrapatellaris, of the saphenous nerve innervates the skin inferior to the Patella. The terminal Branches of the nerve reach the FOOT, innervating the skin of its medial margin.

6. Obturator nerve, nervus obturatorius (L_II-L_IV), emerges from beneath the medial border of the psoas major muscle, descends into the lesser pelvis, and exits onto the thigh through the obturator canal. Here it divides into anterior and posterior branches, rami anterior et posterior. The anterior branch lies between the adductor longus and adductor brevis muscles, which it innervates, and also supplies branches to the pectineus and gracilis muscles, as well as a cutaneous branch, ramus cutaneus, to the skin of the Medial surface of the thigh. The posterior branch lies between the adductor magnus and adductor brevis muscles, and innervates the hip joint and the obturator externus muscle.

Short branches arise directly from the lumbar plexus to the quadratus lumborum, psoas minor, and lateral intertransverse muscles of the lumbar region.

NERVES OF THE LUMBAR PLEXUS

Summary Table

Sacral plexus, plexus sacralis

The sacral plexus is formed by the anterior rami of the fourth and fifth lumbar nerves (lumbosacral trunk), all sacral nerves, and the coccygeal nerve (Fig. 198). The union of the anterior rami of the fifth sacral and coccygeal nerves is designated as the Coccygeal plexus, plexus coccygeus.

The sacral plexus has the shape of a triangular sheet located on the anterior surface of the sacroiliac joint and the piriformis muscle. The apex of the triangle continues into the sciatic nerve, which is the largest in the entire human body (Fig. 198 A).

The branches of the sacral plexus are divided into short and long branches.

Short branches:

1. Muscular branches that pass directly to the piriformis, obturator internus, gemelli, quadratus femoris, levator ani, and coccygeus muscles.

2. Superior gluteal nerve, n. gluteus superior (L_lV-L_V-S_I), emerges from the lesser pelvis through the greater sciatic foramen (foramen suprapiriforme) alongside the Vessels of the same name, enters the gluteal region, and innervates the m. gluteus medius, gluteus minimus, and tensor fasciae latae.

3. Inferior gluteal nerve, nervus gluteus inferior (L_V-S_I-S_II), emerges from the pelvis together with the accompanying vessels through the infrapyramidal foramen (foramen infrapiriforme) and innervates the m. gluteus maximus.

4. Pudendal nerve, nervus pudendus (S_I-S_IV), accompanying the internal pudendal artery (a. pudenda interna), emerges from the pelvis through the infrapyramidal foramen, curves around the ischial spine (spina ischiadica), and through the lesser sciatic foramen (foramen ischiadicum minus) enters the ischioanal fossa (fossa ischiodnale) (Fig. 198 B). It runs along the lateral wall of the fossa, and near the posterior margin of the urogenital Diaphragm divides into its branches: perineal nerves (nеrvі perineales) and the dorsal nerve of the Penis (Clitoris), nervus dorsalis penis (clitoridis). The former innervate the mm. transversus perinei superficialis, bulbospongiosus, and ischiocavernosus, as well as the urethral mucosa, and give off posterior scrotal (labial) nerves, nervi scrotales (labiales) posteriores. The dorsal nerve of the penis (clitoris) accompanies the dorsal artery of the penis or clitoris (a. dorsalis penis/clitoridis), gives off branches to the mm. transversus perinei profundus et sphincter, and passes onto the dorsum of the penis (clitoris).

Within the ischioanal fossa (fossa ischiodnale), the inferior rectal nerves, nervi rectales inferiores, arise from the pudendal nerve, supplying the m. sphincter ani externus and the skin of the anal region.

5. Pelvic splanchnic nerves, nervi splanchnici pelvici, consist of parasympathetic nerve fibers that pass to the inferior hypogastric plexus.

Long branches:

1. Posterior cutaneous nerve of the thigh, nervus cutaneus femoris posterior (SI-SIII), exits the pelvis through the infrapyramidal foramen (Fig. 199), descends along the posterior aspect of the thigh, and innervates its skin. It gives off inferior clunial branches, rаmі сlunіum inferiores, to the skin of the lower part of the buttocks, and perineal branches, rаmі perineales, to the skin of the Perineum.

2. Sciatic nerve, newus ischiadicus [sciaticus] (LNA) (L_IV-S_V) (Fig. 199), emerges from the pelvis through the infrapyramidal foramen, lies anterior to the m. gluteus maximus, and descends, crossing the mm. obturatorius int., gemelli, and quadratus femoris. It emerges onto the thigh from beneath the lower border of the m. gluteus maximus, resting anterior to the Posterior Thigh Muscles. Approaching the upper apex of the popliteal fossa, it divides into its terminal branches: the thicker tibial nerve and the thinner common fibular nerve.

The sciatic nerve innervates the mm. semitendinosus and semimembranosus, the posterior part of the m. adductor magnus, the long HEAD of the m. biceps femoris, and the knee joint.

Tibial nerve, nervus tibialis (L_IV-L_V-S_I-S_II) (Figs. 199, 200), constitutes the medial branch of the sciatic nerve, lying in the middle of the popliteal fossa posterior and lateral to the popliteal vein. Through the adductor canal (canalis cruropopliteus), it passes to the medial malleolus, behind which it divides into its terminal branches: the medial and lateral plantar nerves.

Along its course, the tibial nerve gives off a series of branches:

1) Muscular branches, rami musculares, to the mm. gastrocnemius, soleus, plantaris, popliteus, tibialis posterior, flexor hallucis longus, and flexor digitorum longus.

2) Medial sural cutaneous nerve, nervus cutaneus surae medialis, originates in the popliteal fossa, runs onto the leg alongside the small saphenous vein (v. saphena parva), and innervates the skin of the posteromedial surface of the leg. In the lower third of the leg, it joins with the lateral sural cutaneous nerve to form the sural nerve, nervus suralis. It innervates the skin of the lateral part of the heel (lateral calcaneal branches, rami calcanei laterales), runs along the lateral margin of The Foot as the dorsolateral cutaneous nerve of the foot, nervus cutaneus dorsalis lateralis, reaching the distal phalanx of the fifth digit.

3) Interosseous nerve of the leg, nervus interosseus cruris, which, lying on the interosseous membrane, innervates it, the periosteum of the Tibia, and the ankle joint.

4) Medial calcaneal branches, rami calcanei mediales, supplying the skin of the medial part of the heel.

Medial plantar nerve, nervus plantaris medialis (Fig. 201 A), runs together with the vessels of the same name in the medial plantar sulcus (sulcus plantaris medialis), innervates the muscles of the medial group (except for the m. adductor hallucis and the lateral head of the m. flexor hallucis brevis) and the First and Second mm. lumbricales, and gives off three common plantar digital nerves, nervi digitales plantares communes, which branch into seven proper plantar digital nerves, nervi digitales plantares proprii. The latter innervate the skin of the first through third digits and the medial side of the fourth digit.

Lateral plantar nerve, nervus plantaris lateralis (Fig. 201 A), runs with the accompanying vessels in the lateral plantar sulcus (sulcus plantaris lateralis), innervates all muscles of the lateral group and the m. quadratus plantae, and divides into deep and superficial branches. The former runs along the plantar arterial arch and innervates the third and fourth mm. lumbricales, all mm. interossei, the m. adductor hallucis, and the lateral head of the m. flexor hallucis brevis. The latter divides into two common plantar digital nerves, which in turn branch into three proper plantar digital nerves. The latter innervate the skin of the fifth digit and the lateral side of the fourth digit.

The second terminal branch of the sciatic nerve, the common fibular nerve, nervus fibularis communis (L_IV-L_V-S_I-S_II), branches laterally from the sciatic nerve, curves around the neck of the Fibula, pierces the Water/144.html">Origin of the m. peroneus longus, and divides into its terminal branches: the superficial and deep fibular nerves. Along its course, the common fibular nerve innervates the short head of the m. biceps femoris and gives off the lateral sural cutaneous nerve, nervus cutaneus surae lateralis. The latter supplies the skin of the lateral surface of the leg and communicates with the medial sural cutaneous nerve via a communicating branch, the fibular communicating branch (ramus communicans fibularis), forming the sural nerve, nervus suralis, which innervates the skin of the lower two-thirds of the posterior surface of the calf as well as the lateral margin of the dorsal aspect of the foot.

Fig. 198. Sacral plexus, plexus sacralis (sources of formation and its nerves).

Fig. 198-A. Sacral and coccygeal plexuses, plexus sacralis et coccygeus (after Testut)

Fig. 198-B. Perineal nerves (after F. Kiss and J. Szentágothai)

Fig. 199. Sciatic nerve, nervus ischiadicus

The superficial fibular nerve, nervus fibularis superficialis (Fig. 202), passes through the superior fibular canal (canalis musculoperoneus superior), innervating the fibularis longus and brevis muscles (mm. peroneus longus et brevis). At the border between the middle and lower thirds of the leg, it pierces the fascia, becomes subcutaneous, and descends to the middle of the dorsum of the foot, where it divides into the medial dorsal cutaneous nerve of the foot, nervus cutaneus dorsalis medialis, and the intermediate dorsal cutaneous nerve of the foot, nervus cutaneus dorsalis intermedius. The former divides into three dorsal digital nerves of the foot, nervi digitales dorsales pedis, which supply the skin of the medial side of the great toe, the lateral side of the second toe, and the medial side of the third toe. The latter divides into four dorsal digital nerves of the foot, which supply the skin of the lateral side of the third toe, the dorsal aspect of the fourth toe, and the medial side of the fifth toe.

Fig. 200. Nerves, Arteries, and Veins OF THE right leg (posterior view)

Fig. 202. Nerves of the leg and foot (anterolateral view)

Fig. 201-A. Nerves of the plantar surface of the foot (right)

Fig. 202-A. Cutaneous nerves of the dorsum of the foot (right)

The deep fibular nerve, nervus fibularis profundus (Fig. 202), accompanies the anterior tibial vessels and emerges onto the dorsum of the foot, where it branches into two dorsal digital nerves of the foot, nervi digitales dorsales pedis, supplying the lateral side of the great toe and the medial side of the second toe. Along its course, the nerve gives off muscular branches, rami musculares, to the tibialis anterior, extensor digitorum longus, extensor hallucis longus, extensor digitorum brevis, and extensor hallucis brevis muscles.