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Spinal Each of the 31 pairs of spinal nerves forms from the fusion of t and posterior roots : all that 9 —oyyical ~] Anatomical models and dia rams: ‘ | a sshd h : spinal nerves spinal cord. Rec : x . | aoa anterior roots carry moto plexus | spinal axons emerging from the areca a . oa cord, and the posterior roots carry sensory axons anus ; € spinal cord. Each spinal nerve carries both motor and sensory axons, so all spinal nerves are mixed nerves oots fuse Shortly after the anterior and posterior f to form the spinal nerve, it splits into three branches: 4 posterior ramus, an anterior ramus, and a small meni geal branch. The posterior rami serve the skin, joints, and musculature of the posterior trunk. The meningeal ate spina Pac ata —S eneN T ~ branches reenter the vertebral canal to innerv structures. The larger anterior rami (RAY-mees ramus, ie singular; “branch”) travel anteriorly to supply the ; muscles of the upper and lower limbs, the anterior ccs a f the back. The gener al lexus thorax and abdomen, and part 0 wD ustrated in Figut ag distribution of the anterior rami is ill 14.6 and 14.7. The anterior rami of the thorac 14. travel between the ribs as 11 separate pairs 0 nerves that innervate the intercostal muscles, the abdominal muscles, and the Lateral femoral cutaneous nerve ic spinal nerves f intercostal Femoral nerve IMI} , " . Fe enriiis, = . er ee ry eS SRT Vicks — ee : ao es oe SS id ees * os s, af Yes se Peo its La va) ig si ee sii 2 " AS ‘ Qo FP oe ro i . ~ ee Se ee = A na ag ee ee ee } i _ ot eld aT LA a? Mie | he =, rachial, lumbar, and sacral plexuses. The major nerves of these plexuses are as follows: 1. Cervical plexuses. The c the anterior rami of C1- tions from CS. The branches 0 serve the skin of the head and the neck neck muscles. The major branch is the phrenic # nerve (FREN-ik; phren- = “diaphragm;” C3-C5), Tibia nerve which serves the diaphragm muscle, and triggers the process of inspiration during breathing. ; ist Of ‘ati ervical plexuses consis Sciatic nerve C4 with small contribu- f each cervical plexus and certain Common fibular nerve 2. Brachial plexuses. The complicated-looking brachial plexuses consist of the anterior rami of C5-T1 (Fig. 14.8). The first structures formed in each brachial plexus are its large trunks. Typically, C5 and C6 unite to form the superior trunk, C7 forms the middle trunk, and C8 and T1 unite to form th inferior trunk. Each trunk splits into an ante ; division and a posterior division that beco re cords of the plexus. The anterior divisio ft = inferior trunk forms the medial cord es a descends in the medial arm. Th dias divisions of the superior a Trg middle trunks unite to form the la 14 teral cord whi , Which descend FIGU 2 R RE .6 N erve plexuses and the anteriar rami 
