1. PowerPoint ® Lecture Slides prepared by Janice Meeking, Mount Royal College C H A P T E R Copyright © 2010 Pearson Education, Inc. 13 The Peripheral Nervous System and Reflex Activity: Part C

2. 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 )

3. Copyright © 2010 Pearson Education, Inc. Figure 13.6 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 Cervical plexus Intercostal nerves Cervical enlargement Lumbar enlargement Cauda equina Brachial plexus Lumbar plexus Sacral plexus

4. Copyright © 2010 Pearson Education, Inc. 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

5. 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

6. Copyright © 2010 Pearson Education, Inc. Figure 13.7 (a) Dorsal root ganglion Gray matter White matter Ventral root Dorsal root Dorsal and ventral rootlets of spinal nerve Dorsal ramus of spinal nerve Ventral ramus of spinal nerve Sympathetic trunk ganglion Spinal nerve Rami communicantes 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.

7. Copyright © 2010 Pearson Education, Inc. 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

8. 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

9. Copyright © 2010 Pearson Education, Inc. Figure 13.7 (b) Dorsal ramus Ventral ramus Intercostal nerve Spinal nerve Rami communicantes Dorsal root ganglion Dorsal root Ventral root Sympathetic trunk ganglion Sternum (b) Cross section of thorax showing the main roots and branches of a spinal nerve. Branches of intercostal nerve Lateral cutaneous Anterior cutaneous

10. Copyright © 2010 Pearson Education, Inc. 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 )

11. Copyright © 2010 Pearson Education, Inc. 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

12. Copyright © 2010 Pearson Education, Inc. 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

13. Copyright © 2010 Pearson Education, Inc. 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

14. Copyright © 2010 Pearson Education, Inc. Figure 13.10 (a) Ventral rami and major branches of the lumbar plexus Iliohypogastric L1L1 L2L2 L3L3 L4L4 L5L5 Ilioinguinal Genitofemoral Lateral femoral cutaneous Obturator Femoral Lumbosacral trunk Lateral femoral cutaneous Anterior femoral cutaneous Saphenous Obturator Iliohypogastric Ilioinguinal Femoral Ventral rami Ventral rami: (b) Distribution of the major nerves from the lumbar plexus to the lower limb

15. Copyright © 2010 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 the body Innervates the hamstring muscles, adductor magnus, and most muscles in the leg and foot Composed of two nerves: tibial and common fibular

16. Copyright © 2010 Pearson Education, Inc. Figure 13.11 (a) Superior gluteal Lumbosacral trunk Inferior gluteal Common fibular Tibial Posterior femoral cutaneous Pudendal Sciatic Ventral rami and major branches of the sacral plexus L4L4 L5L5 S1S1 S2S2 S3S3 S4S4 S5S5 Co 1 Ventral rami Ventral rami:

17. Copyright © 2010 Pearson Education, Inc. Figure 13.11 (b) Superior gluteal Inferior gluteal Common fibular Deep fibular Superficial fibular Plantar branches Tibial Sural (cut) Posterior femoral cutaneous Pudendal Sciatic (b) Distribution of the major nerves from the sacral plexus to the lower limb

18. Copyright © 2010 Pearson Education, Inc. 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

19. Copyright © 2010 Pearson Education, Inc. 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