© 2013 Pearson Education, Inc. Spinal Nerves 31 pairs of mixed nerves named for point of issue from spinal cord –Supply all body parts but head and part of neck –8 cervical (C 1 –C 8 ) –12 thoracic (T 1 –T 12 ) –5 Lumbar (L 1 –L 5 ) –5 Sacral (S 1 –S 5 ) –1 Coccygeal (C 0 )

© 2013 Pearson Education, Inc. Spinal Nerves Only 7 cervical vertebrae, yet 8 pairs cervical spinal nerves –7 exit vertebral canal superior to vertebrae for which named –1 exits canal inferior to C 7 Other vertebrae exit inferior to vertebra for which named

© 2013 Pearson Education, Inc. Figure 13.7 Spinal nerves. Cervical plexus Brachial plexus Cervical enlargement Intercostal nerves Lumbar enlargement Lumbar plexus Sacral plexus Cauda equina Cervical nerves C 1 – C 8 Thoracic nerves T 1 – T 12 Lumbar nerves L 1 – L 5 Sacral nerves S 1 – S 5 Coccygeal nerve Co 1

© 2013 Pearson Education, Inc. Spinal Nerves: Roots Each spinal nerve connects to spinal cord via two roots Ventral roots –Contain motor (efferent) fibers from ventral horn motor neurons –Fibers innervate skeletal muscles

© 2013 Pearson Education, Inc. Spinal Nerves: Roots Dorsal roots –Contain sensory (afferent) fibers from sensory neurons in dorsal root ganglia and conduct impulses from peripheral receptors Dorsal and ventral roots unite to form spinal nerves, which emerge from vertebral column via intervertebral foramina

© 2013 Pearson Education, Inc. Figure 13.8a Formation of spinal nerves and rami distribution. Gray matter White matter Dorsal root Dorsal and ventral rootlets of spinal nerve Dorsal root ganglion Dorsal ramus of spinal nerve Ventral ramus of spinal nerve Spinal nerve Sympathetic trunk ganglion Anterior view showing spinal cord, associated nerves, and vertebrae. The dorsal and ventral roots arise medially as rootlets and join laterally to form the spinal nerve. Rami communicantes Ventral root

© 2013 Pearson Education, Inc. Spinal Nerves: Rami All ventral rami except T 2 –T 12 form interlacing nerve networks called nerve plexuses (cervical, brachial, lumbar, and sacral) Back innervated by dorsal rami via several branches Ventral rami of T 2 –T 12 as intercostal nerves supply muscles of ribs, anterolateral thorax, and abdominal wall Spinal roots longer as move inferiorly in cord –Lumbar and sacral roots extend as cauda equina

© 2013 Pearson Education, Inc. Spinal Nerves: Plexuses Within plexus fibers criss-cross –Each branch contains fibers from several spinal nerves –Fibers from ventral ramus go to body periphery via several routes Each limb muscle innervated by more than one spinal nerve –Damage to one does not  paralysis

© 2013 Pearson Education, Inc. Dorsal ramus Ventral ramus Spinal nerve Rami communicantes Sympathetic trunk ganglion Dorsal root ganglion Dorsal root Ventral root Branches of intercostal nerve Lateral cutaneous Anterior cutaneous Sternum Intercostal nerve Cross section of thorax showing the main roots and branches of a spinal nerve. Figure 13.8b Formation of spinal nerves and rami distribution.

© 2013 Pearson Education, Inc. Cervical Plexus and the Neck Formed by ventral rami of C 1 –C 4 Most branches form cutaneous nerves –Innervate skin of neck, ear, back of head, and shoulders –Other branches innervate neck muscles Phrenic nerve –Major motor and sensory nerve of diaphragm (receives fibers from C 3 –C 5 ) –Irritation  hiccups

© 2013 Pearson Education, Inc. Ventral rami Ventral rami: Hypoglossal nerve (XII) Lesser occipital nerve Greater auricular nerve Transverse cervical nerve Ansa cervicalis Accessory nerve (XI) Phrenic nerve Supraclavicular nerves Segmental branches C1C1 C2C2 C3C3 C4C4 C5C5 Figure 13.9 The cervical plexus.

© 2013 Pearson Education, Inc. Brachial Plexus and Upper Limb Formed by ventral rami of C 5 –C 8 and T 1 (and often C 4 and/or T 2 ) Gives rise to nerves that innervate upper limb Major branches of this plexus: –Roots—five ventral rami (C 5 –T 1 ), which form –Trunks—upper, middle, and lower, which form –Divisions—anterior and posterior, which form –Cords—lateral, medial, and posterior

© 2013 Pearson Education, Inc. Anterior divisions Roots (ventral rami): Posterior divisions TrunksRoots Dorsal scapular Nerve to subclavius Suprascapular Posterior divisions Lateral Posterior Medial Axillary Musculo- cutaneous Radial Median Ulnar Upper Middle Lower Long thoracic Medial pectoral Lateral pectoral Upper subscapular Lower subscapular Thoracodorsal Medial cutaneous nerves of the arm and forearm C4C4 C5C5 C6C6 C7C7 C8C8 T1T1 Trunks Roots (rami C 5 –T 1 ), trunks, divisions, and cords Cords Figure 13.10a The brachial plexus.

© 2013 Pearson Education, Inc. C5C5 Flowchart summarizing relationships within the brachial plexus C6C6 C7C7 C8C8 T1T1 Major terminal branches (peripheral nerves) Cords Divisions Roots (ventral rami) Trunks Musculocutaneous Median Ulnar Radial Axillary Lateral Medial Posterior Anterior Posterior Anterior Posterior Anterior Posterior Upper Middle Lower Figure 13.10b The brachial plexus.

© 2013 Pearson Education, Inc. Brachial Plexus: Five Important Nerves Axillary—innervates deltoid, teres minor, and skin and joint capsule of shoulder Musculocutaneous—innervates biceps brachii and brachialis, and skin of lateral forearm Median—innervates skin, most flexors, forearm pronators, wrist and finger flexors Ulnar—supplies flexor carpi ulnaris, part of flexor digitorum profundus, skin of medial aspect of hand, wrist/finger flexion Radial—innervates essentially all extensor muscles, supinators, and posterior skin of limb

© 2013 Pearson Education, Inc. Humerus Axillary nerve Radial nerve Musculocutaneous nerve Ulna Radius Ulnar nerve Median nerve Radial nerve (superficial branch) Dorsal branch of ulnar nerve Superficial branch of ulnar nerve Digital branch of ulnar nerve Muscular branch Digital branch Median nerve The major nerves of the upper limb Figure 13.10c The brachial plexus.

© 2013 Pearson Education, Inc. Lumbar Plexus Arises from L 1 –L 4 Innervates thigh, abdominal wall Femoral nerve—innervates quadriceps and skin of anterior thigh and medial surface of leg Obturator nerve—passes through obturator foramen to innervate adductor muscles

© 2013 Pearson Education, Inc. Figure The lumbar plexus. Ventral rami Iliohypogastric Ilioinguinal Genitofemoral Lateral femoral cutaneous Obturator Femoral Lumbosacral trunk Iliohypogastric Ilioinguinal Femoral Lateral femoral cutaneous Obturator Anterior femoral cutaneous Saphenous Ventral rami: Ventral rami and major branches of the lumbar plexus Distribution of the major nerves from the lumbar plexus to the lower limb L1L1 L2L2 L3L3 L4L4 L5L5

© 2013 Pearson Education, Inc. Sacral Plexus Arises from L 4 –S 4 Serves the buttock, lower limb, pelvic structures, and perineum Sciatic nerve –Longest and thickest nerve of body –Innervates hamstring muscles, adductor magnus, and most muscles in leg and foot –Composed of two nerves: tibial and common fibular

© 2013 Pearson Education, Inc. Ventral rami Ventral rami and major branches of the sacral plexus Superior gluteal Lumbosacral trunk Inferior gluteal Common fibular Tibial Posterior femoral cutaneous Pudendal Sciatic Ventral rami: L4L4 L5L5 S1S1 S2S2 S3S3 S4S4 S5S5 Co 1 Figure 13.12a The sacral plexus.

© 2013 Pearson Education, Inc. Superior gluteal Inferior gluteal Pudendal Sciatic Posterior femoral cutaneous Common fibular Tibial Sural (cut) Deep fibular Superficial fibular Plantar branches Distribution of the major nerves from the sacral plexus to the lower limb Figure 13.12b The sacral plexus.

© 2013 Pearson Education, Inc. Anterolateral Thorax and Abdominal Wall Ventral rami in thorax in simple segmental pattern –Form intercostal nerves that supply intercostal muscles, muscle and skin of anterolateral thorax, most abdominal wall Dorsal rami innervate posterior body trunk

© 2013 Pearson Education, Inc. Innervation of Skin: Dermatomes Dermatome - area of skin innervated by cutaneous branches of single spinal nerve All spinal nerves except C 1 participate in dermatomes Most dermatomes overlap, so destruction of a single spinal nerve will not cause complete numbness

© 2013 Pearson Education, Inc. Figure Map of dermatomes. C2 C3 C4 C5 T5 T4 T3 T2 T1 T6 T7 T8 T9 T10 T2 T11 T2 C5 C6 C7 C8 T12 L1 L2 S2 S3 C8 C5 C6 C7 L3 L4 L5 L4 L3 S1 C2 C3 C4 C5 C6 C7 C8 T1 T2 T3 T4 T5 T6 T7 T8 T9 T10 C5 C6 C7 C8 L2 L4 S1 T11 T12 L1 L3 L5 C8 C6 C7 S2 S3 S4 S5 S1 S2 S1 L1 L2 L5 L3 L4 L5 L4 S1 Posterior view Anterior view