Human Anatomy - Kotsan I. Y. 2009

Peripheral Nervous System
Spinal Nerves
Long branches of the sacral plexus

The Long Branches of the Sacral Plexus include the posterior cutaneous nerve of the thigh and the sciatic nerve.

The posterior cutaneous nerve of the thigh (n. cutaneus femoris posterior) (S_I-S_III) is a sensory branch of the sacral plexus. It exits the pelvic cavity through the infrapiriform foramen, medial to the sciatic nerve, passes inferiorly beneath the gluteus maximus Muscle into the posterior femoral region, pierces the fascia lata, and terminates in branches that supply the Skin of the posterior surface of the thigh down to and including the popliteal fossa.

At the level of the inferior margin of the gluteus maximus muscle, the posterior cutaneous nerve of the thigh gives rise to the following nerves: inferior cluneal nerves (rr. clunium inferiores), which innervate the skin of the lower gluteal region, and perineal branches (rr. perineales), which innervate the skin of the Perineum and the medial aspect of the Scrotum (or Labia Majora in females).

The sciatic nerve (n. ischiadicus) (L_IV-L_V, S_I-S_III) is the largest nerve in The Human Body and the direct continuation of the sacral plexus. It emerges from the pelvic cavity through the infrapiriform foramen, lying lateral to the other nerves and vessels, passes beneath the gluteus maximus muscle lateral to the ischial tuberosity, and descends in the posterior region of the thigh between the semimembranosus and biceps femoris Muscles, reaching the popliteal fossa. At the superior apex of the popliteal fossa, the sciatic nerve divides into its two main branches: the tibial and common fibular nerves. Frequently, division into these two major branches may occur higher, above the popliteal fossa, or even within the pelvic cavity.

The branches originating from the sciatic nerve include muscular branches, the tibial nerve, and the common fibular nerve.

The muscular branches (rr. musculares) innervate the obturator internus, superior and inferior gemelli, adductor magnus, and the Posterior Thigh Muscles—the semitendinosus, semimembranosus, and biceps femoris (excluding the short HEAD, which is innervated by the common fibular nerve).

The tibial nerve (n. tibialis) (L_IV-L_V, S_I-S_II) is the continuation of the sciatic nerve trunk down the leg, running straight down the middle of the popliteal fossa along the path of the popliteal vessels, and then entering the popliteal-crural canal. The tibial nerve emerges from the popliteal-crural canal posterior to the medial malleolus, curves around it by passing beneath the flexor retinaculum, and divides into its terminal branches: the medial and lateral plantar nerves.

In the popliteal fossa, the tibial nerve gives off muscular branches (rr. musculares) to the gastrocnemius, soleus, plantaris, and popliteus muscles, as well as a sensory branch to the knee joint. Additionally, within the popliteal fossa, the tibial nerve gives rise to the medial sural cutaneous nerve (n. cutaneus surae medialis), which descends alongside the small saphenous vein and innervates the skin of the posteromedial surface of the leg.

In the leg, the tibial nerve gives off the interosseous nerve of the leg (n. interosseus cruris), which innervates all three deep muscles—the tibialis posterior, flexor hallucis longus, and flexor digitorum longus—as well as the posterior aspect of the ankle joint, the skin of the heel, and the medial margin of the FOOT.

The medial plantar nerve (n. plantaris medialis) is one of the terminal Branches of the tibial nerve. It runs along the medial margin of the tendon of the flexor digitorum brevis within the medial plantar sulcus, accompanied by the medial plantar artery. At the level of the metatarsal bases, the medial plantar nerve gives off the first proper plantar digital nerve (n. digitalis plantaris proprius) to the skin of the medial margin of the foot and the big toe, as well as three common plantar digital nerves (nn. digitales plantares communes). At the level of the Base of the toes, each of these three nerves divides into two proper plantar digital nerves (nn. digitales plantares proprii), which innervate the skin of the opposing sides of the digits.

The medial plantar nerve also innervates several plantar muscles: the flexor hallucis brevis, abductor hallucis, flexor digitorum brevis, and the First and Second lumbricals.

The lateral plantar nerve (n. plantaris lateralis) is the second terminal branch of the tibial nerve. It passes beneath the flexor digitorum brevis to reach the lateral plantar sulcus, where it divides proximally into deep and superficial branches. The deep branch (r. profundus) of the lateral plantar nerve runs within the lateral plantar sulcus and innervates the adductor hallucis, flexor hallucis brevis (deep head), and the II-IV lumbricals. The superficial branch (r. superficialis) of the lateral plantar nerve gives off a proper plantar nerve laterally to the fifth digit (n. digitalis plantaris proprius), which innervates the skin of the plantar surface and lateral side of the little toe. Medially, a common plantar digital nerve (n. digitalis plantaris communis) arises from the superficial branch; it divides into two proper plantar nerves (nn. digitales plantares proprii) that supply the skin of the opposing sides of the IV and V toes.

The medial and lateral plantar nerves also innervate the JOINTS OF THE foot. Furthermore, muscular branches (rr. musculares) arise from the lateral plantar nerve to supply the quadratus plantae and the abductor digiti minimi.

The common fibular nerve (n. fibularis communis) (L_IV, L_V, S_I, S_II) extends downward from the point of bifurcation of the sciatic nerve along the medial margin of the long head of the biceps femoris and the medial margin of its tendon, reaching the head of the Fibula. The nerve then courses anteriorly and obliquely, winding around the neck of the fibula, and divides into two branches: the superficial and deep fibular nerves.

In the popliteal fossa, the lateral sural cutaneous nerve (n. cutaneus surae lateralis) branches off the common fibular nerve to supply the skin of the lateral aspect of the leg. In the lower third of the leg, the lateral sural cutaneous nerve unites with the medial sural cutaneous nerve to form the sural nerve (n. suralis). The sural nerve passes posterior to the lateral malleolus, sending branches to the heel skin, and continues along the lateral border of the dorsal foot as the lateral dorsal cutaneous nerve (n. cutaneus dorsalis lateralis), innervating the skin of this border and the lateral surface of the little toe.

The superficial fibular nerve (n. fibularis superficialis) runs through the superior musculoperoneal canal between the fibula and the belly of the fibularis longus muscle, entering the anterior fibular compartment at the junction of the middle and lower thirds of the leg. The nerve then descends between the fibular muscles and the extensor digitorum longus, pierces the crural fascia, and divides into its terminal branches. One of these, the medial dorsal cutaneous nerve (n. cutaneus dorsalis medialis), runs toward the medial margin of the foot, supplying the skin of this region, the medial side of the big toe, and the opposing skin surfaces of the II and III toes. The second branch, the intermediate dorsal cutaneous nerve (n. cutaneus dorsalis intermedius), descends along the anterolateral surface of the foot and divides into dorsal digital NERVES OF THE foot (nn. digitales dorsales pedis), which innervate the skin of the opposing surfaces of the III, IV, and V toes. Along its course, the superficial fibular nerve also gives off muscular branches (rr. musculares) supplying the fibularis longus, brevis, and tertius muscles.

The deep fibular nerve (n. fibularis profundus) courses anteriorly from the point of division of the common fibular nerve, pierces the fibularis longus and the anterior intermuscular septum of the leg, and enters the anterior compartment of the leg. The nerve then descends along the anterior surface of the interosseous membrane of the leg, passes beneath the extensor retinaculum, and reaches the dorsum of the foot, where it divides into two dorsal digital nerves of the foot (nn. digitales dorsales pedis) that innervate the skin of the opposing surfaces of the I and II toes.

Muscular branches (rr. musculares) also arise from the deep fibular nerve, supplying the tibialis anterior, extensor digitorum longus, extensor hallucis longus, extensor digitorum brevis, and extensor hallucis brevis. In addition, the deep fibular nerve supplies articular branches to the ankle joint.

Data on the major nerves of the sacral plexus are presented in Table 12.

Class="center">Table 12 NERVES OF THE SACRAL PLEXUS