CHAPTER 13c THE PERIPHERAL NERVOUS SYSTEM REFLEX ACTIVITY

CHAPTER # 13(c) THE PERIPHERAL NERVOUS SYSTEM & REFLEX ACTIVITY Copyright © 2010 Pearson Education, Inc.

Spinal Nerves • 31 pairs of mixed nerves named according to their point of issue from the spinal cord • 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) Copyright © 2010 Pearson Education, Inc.

Cervical plexus Brachial plexus Cervical enlargement Intercostal nerves Cervical nerves C 1 – C 8 Thoracic nerves T 1 – T 12 Lumbar enlargement Lumbar plexus Sacral plexus Cauda equina Copyright © 2010 Pearson Education, Inc. Lumbar nerves L 1 – L 5 Sacral nerves S 1 – S 5 Coccygeal nerve Co 1 Figure 13. 6

Spinal Nerves: Roots • Each spinal nerve connects to the spinal cord via two roots • Ventral roots • Contain motor (efferent) fibers from the ventral horn motor neurons • Fibers innervate skeletal muscles) Copyright © 2010 Pearson Education, Inc.

Spinal Nerves: Roots • Dorsal roots • Contain sensory (afferent) fibers from sensory neurons in the dorsal root ganglia • Conduct impulses from peripheral receptors • Dorsal and ventral roots unite to form spinal nerves, which then emerge from the vertebral column via the intervertebral foramina Copyright © 2010 Pearson Education, Inc.

Dorsal root ganglion Dorsal ramus of spinal nerve Ventral ramus of spinal nerve Spinal nerve Gray matter White matter Ventral root Dorsal and ventral rootlets of spinal nerve Rami communicantes 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. Copyright © 2010 Pearson Education, Inc. Figure 13. 7 (a)

Spinal Nerves: Rami • Each spinal nerve branches into mixed rami • Dorsal ramus • Larger ventral ramus • Meningeal branch • Rami communicantes (autonomic pathways) join to the ventral rami in the thoracic region Copyright © 2010 Pearson Education, Inc.

Spinal Nerves: Rami • All ventral rami except T 2–T 12 form interlacing nerve networks called plexuses (cervical, brachial, lumbar, and sacral) • The back is innervated by dorsal rami via several branches • Ventral rami of T 2–T 12 as intercostal nerves supply muscles of the ribs, anterolateral thorax, and abdominal wall Copyright © 2010 Pearson Education, Inc.

Dorsal ramus Ventral ramus Spinal nerve Rami communicantes Sympathetic trunk ganglion Intercostal nerve Dorsal root ganglion Dorsal root Ventral root Branches of intercostal nerve • Lateral cutaneous • Anterior cutaneous Sternum (b) Cross section of thorax showing the main roots and branches of a spinal nerve. Copyright © 2010 Pearson Education, Inc. Figure 13. 7 (b)

Cervical Plexus • Formed by ventral rami of C 1–C 4 • Innervates skin and muscles of the neck, ear, back of head, and shoulders • Phrenic nerve • Major motor and sensory nerve of the diaphragm (receives fibers from C 3–C 5) Copyright © 2010 Pearson Education, Inc.

Ventral rami Segmental branches Hypoglossal nerve (XII) Lesser occipital nerve Greater auricular nerve Transverse cervical nerve Ansa cervicalis Accessory nerve (XI) Phrenic nerve Ventral rami: C 1 C 2 C 3 C 4 C 5 Supraclavicular nerves Copyright © 2010 Pearson Education, Inc. Figure 13. 8

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Brachial Plexus • Formed by ventral rami of C 5–C 8 and T 1 (and often C 4 and T 2) • It gives rise to the nerves that innervate the upper limb • Major branches of this plexus: • Roots—five ventral rami (C 5–T 1) • Trunks—upper, middle, and lower • Divisions—anterior and posterior • Cords—lateral, medial, and posterior Copyright © 2010 Pearson Education, Inc.

Posterior divisions Cords Roots (ventral rami): C 4 C 5 Dorsal scapular Nerve to subclavius Suprascapular C 6 C 7 Lateral C 8 Posterior T 1 Medial Axillary Musculocutaneous Radial Median Ulnar (a) Roots (rami C 5 – T 1), trunks, divisions, and cords Anterior divisions Copyright © 2010 Pearson Education, Inc. Posterior divisions Trunks Upper Middle Trunks Lower Long thoracic Medial pectoral Lateral pectoral Upper subscapular Lower subscapular Thoracodorsal Medial cutaneous nerves of the arm and forearm Roots Figure 13. 9 (a)

Anterior divisions Posterior divisions Major terminal branches (peripheral nerves) Musculocutaneous Median Ulnar Radial Axillary Trunks Cords Roots Divisions Anterior Lateral Posterior Medial Anterior Posterior Trunks Upper Roots (ventral rami) C 5 C 6 Middle C 7 C 8 Lower T 1 (d) Flowchart summarizing relationships within the brachial plexus Copyright © 2010 Pearson Education, Inc. Figure 13. 9 (d)

Brachial Plexus: Nerves • Axillary—innervates the deltoid, teres minor, and skin and joint capsule of the shoulder • Musculocutaneous—innervates the biceps brachii and brachialis and skin of lateral forearm • Median—innervates the skin, most flexors and pronators in the forearm, and some intrinsic muscles of the hand • Ulnar—supplies the flexor carpi ulnaris, part of the flexor digitorum profundus, most intrinsic muscles of the hand, and skin of medial aspect of hand • Radial—innervates essentially all extensor muscles, supinators, and posterior skin of limb Copyright © 2010 Pearson Education, Inc.

Axillary nerve Anterior divisions Posterior divisions Trunks Roots Humerus 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 Median nerve Digital branch (c) The major nerves of the upper limb Copyright © 2010 Pearson Education, Inc. Figure 13. 9 (c)

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Lumbar Plexus • Arises from L 1–L 4 • Innervates the thigh, abdominal wall, and psoas muscle • Femoral nerve—innervates quadriceps and skin of anterior thigh and medial surface of leg • Obturator nerve—passes through obturator foramen to innervate adductor muscles Copyright © 2010 Pearson Education, Inc.

Ventral rami Iliohypogastric Ilioinguinal Genitofemoral Lateral femoral cutaneous Obturator Femoral Lumbosacral trunk Ventral rami: Iliohypogastric L 1 Ilioinguinal Femoral Lateral femoral L 2 cutaneous Obturator L 3 Anterior femoral cutaneous Saphenous L 4 L 5 (a) Ventral rami and major branches of the lumbar plexus (b) Distribution of the major nerves from the lumbar plexus to the lower limb Copyright © 2010 Pearson Education, Inc. Figure 13. 10

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Sacral Plexus • Arises from L 4–S 4 • Serves the buttock, lower limb, pelvic structures, and perineum • Sciatic nerve • Longest and thickest nerve of the body • Innervates the hamstring muscles, adductor magnus, and most muscles in the leg and foot • Composed of two nerves: tibial and common fibular Copyright © 2010 Pearson Education, Inc.

Ventral rami: L 4 Superior gluteal Lumbosacral trunk Inferior gluteal Common fibular Tibial Posterior femoral cutaneous Pudendal Sciatic L 5 S 1 S 2 S 3 S 4 S 5 Co 1 Ventral rami and major branches of the sacral plexus Copyright © 2010 Pearson Education, Inc. Figure 13. 11 (a)

Superior gluteal Inferior gluteal Pudendal Sciatic Posterior femoral cutaneous Common fibular Tibial Sural (cut) Deep fibular Superficial fibular Plantar branches (b) Distribution of the major nerves from the sacral plexus to the lower limb Copyright © 2010 Pearson Education, Inc. Figure 13. 11 (b)

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Innervation of Skin • Dermatome: the area of skin innervated by the cutaneous branches of a 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 Copyright © 2010 Pearson Education, Inc.

C 2 C 3 C 4 C 5 C 6 C 7 C 8 T 1 T 2 T 3 T 4 T 5 T 6 T 7 T 8 T 9 T 10 C 2 C 3 C 4 C 5 T 1 T 2 T 3 T 4 T 5 T 6 T 7 T 8 T 9 T 10 T 11 T 2 C 5 C 6 C 7 L 1 C 8 L 2 T 12 S 3 T 2 C 5 C 6 L 1 C 8 L 2 S 1 L 4 S 2 S 3 S 4 S 5 C 6 C 7 S 2 C 6 C 7 C 8 S 1 L 3 L 5 L 4 T 11 T 12 L 1 L 3 L 5 C 7 C 6 S 1 S 2 L 3 C 5 L 2 L 5 L 4 L 3 L 5 L 4 S 1 Anterior view Copyright © 2010 Pearson Education, Inc. S 1 (b) Posterior view L 4 L 5 S 1 Figure 13. 12

Innervation of Joints • Hilton’s law: Any nerve serving a muscle that produces movement at a joint also innervates the joint and the skin over the joint Copyright © 2010 Pearson Education, Inc.