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The Nervous System PNS CRANIAL NERVES SPINAL NERVES Peripheral Nervous System (PNS) All neural structures outside the brain Sensory receptors Peripheral nerves and associated ganglia Motor neuron endings Pathway between CNS and outlying structures 12 pairs of cranial nerves 31 pairs of spinal nerves Central nervous system (CNS) Peripheral nervous system (PNS) Sensory (afferent) division Motor (efferent) division Somatic nervous system Autonomic nervous system (ANS) Sympathetic division Parasympathetic division Figure 13.1 Endoneurium Axon Myelin sheath Perineurium Epineurium Fascicle Blood vessels (b) Figure 13.3b Cranial Nerves 12 pairs of nerves Associated with the brain Most are mixed in function Only 2 pairs are purely sensory Each nerve is identified by Number (I through XII) Name “On occasion, our trusty truck acts funny—very good vehicle anyhow” Frontal lobe Temporal lobe Infundibulum Facial nerve (VII) Vestibulocochlear nerve (VIII) Glossopharyngeal nerve (IX) Vagus nerve (X) Accessory nerve (XI) Hypoglossal nerve (XII) Filaments of olfactory nerve (I) Olfactory bulb Olfactory tract Optic nerve (II) Optic chiasma Optic tract Oculomotor nerve (III) Trochlear nerve (IV) Trigeminal nerve (V) Abducens nerve (VI) Cerebellum Medulla oblongata (a) Figure 13.5 (a) Cranial nerves I – VI I II III IV V Olfactory Optic Oculomotor Trochlear Trigeminal VI Abducens Cranial nerves VII – XII VII Facial VIII Vestibulocochlear IX X XI XII (b) Glossopharyngeal Vagus Accessory Hypoglossal Sensory function Motor function PS* fibers Yes (smell) Yes (vision) No No Yes (general sensation) No No Yes Yes Yes No No Yes No No No Yes No Sensory function Motor function PS* fibers Yes (taste) Yes (hearing and balance) Yes Some Yes No Yes (taste) Yes (taste) No No Yes Yes Yes Yes Yes Yes No No *PS = parasympathetic Figure 13.5 (b) Table 13.2 Table 13.2 Table 13.2 Table 13.2 Table 13.2 Table 13.2 Activity Complete Cranial Nerve Chart Spinal Nerves 31 pairs of mixed nerves named according to their point of issue from the spinal cord 8 cervical (C1–C8) 12 thoracic (T1–T12) 5 Lumbar (L1–L5) 5 Sacral (S1–S5) 1 Coccygeal (C0) Cervical plexus Brachial plexus Cervical enlargement Intercostal nerves Cervical nerves C1 – C8 Thoracic nerves T1 – T12 Lumbar enlargement Lumbar plexus Sacral plexus Cauda equina Lumbar nerves L 1 – L5 Sacral nerves S1 – S5 Coccygeal nerve Co1 Figure 13.6 Spinal Nerve Organization 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 Dorsal roots Contain sensory (afferent) fibers from sensory neurons in the dorsal root ganglia Conduct impulses from peripheral receptors Spinal Nerve Organization Dorsal and ventral roots unite to form spinal nerves Emerge from vertebral column via the intervertebral foramina Spinal Nerve Organization Rami Each spinal nerve branches into mixed rami Dorsal ramus Ventral ramus Rami communicantes (autonomic pathways) join to the ventral rami in the thoracic region Meningeal branch Gray matter White matter Ventral root Dorsal root Dorsal root ganglion Dorsal ramus of spinal nerve Ventral ramus of spinal nerve Spinal nerve 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. Figure 13.7 (a) Spinal Nerve Organization Dorsal ramus Innervates Deep back muscles Posterior surface of trunk Ventral ramus Innervates Superficial back muscles Limbs Lateral and anterior surfaces of trunk 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. Figure 13.7 (b) Distribution of Spinal Nerves Dermatome Area of skin innervated by the cutaneous branches of a single spinal nerve All spinal nerves except C1 participate in dermatomes Most dermatomes overlap C2 C3 C4 C5 C6 C7 C8 T1 T2 T3 T4 T5 T6 T7 T8 T9 T10 C2 C3 C4 C5 T1 T2 T3 T4 T5 T6 T7 T8 T9 T10 T11 T2 C5 C6 C6 C7 L1 C8 L2 T12 S2 S3 T2 C5 C6 L1 C8 L2 S1 L4 S2 S3 S4 S5 C6 C7 C6 C7 C8 C8 L2 S2 S1 L1 L3 L5 L4 T11 T12 L1 L3 L5 C7 C6 S1 S2 L3 C5 L2 L5 L4 L3 L5 L5 L4 S1 Anterior view S1 (b) Posterior view L4 L5 L4 L5 S1 Figure 13.12 Plexuses All ventral rami form interlacing nerve networks 4 plexuses Cervical, brachial, lumbar, and sacral Exception: ventral rami of T2–T12 Do not form a plexus Form intercostal nerves Cervical plexus Brachial plexus Cervical enlargement Intercostal nerves Cervical nerves C1 – C8 Thoracic nerves T1 – T12 Lumbar enlargement Lumbar plexus Sacral plexus Cauda equina Lumbar nerves L 1 – L5 Sacral nerves S1 – S5 Coccygeal nerve Co1 Figure 13.6 Plexuses Cervical plexus Formed by ventral rami of C1–C4 Innervates skin & muscles of the neck, ear, back of head, and shoulders Phrenic nerve Major motor and sensory nerve of the diaphragm Receives fibers from C3–C5 Ventral rami Segmental branches Hypoglossal nerve (XII) Lesser occipital nerve Greater auricular nerve Transverse cervical nerve Ansa cervicalis Ventral rami: C1 C2 C3 C4 Accessory nerve (XI) Phrenic nerve C5 Supraclavicular nerves Figure 13.8 Plexuses Brachial plexus Formed by ventral rami of C4– T1 Gives rise to the nerves that innervate the upper limb Median Ulnar Axillary Radial Musculocutaneous Roots (ventral rami): C4 C5 Dorsal scapular Nerve to subclavius Suprascapular Cords C6 Posterior divisions C7 Lateral C8 Posterior T1 Upper Middle Trunks Lower Long thoracic Medial pectoral Medial Lateral pectoral Axillary Musculocutaneous Radial Median Ulnar Upper subscapular Lower subscapular Thoracodorsal (a) Roots (rami C5 – T1), trunks, divisions, and cords Anterior divisions Posterior divisions Trunks Medial cutaneous nerves of the arm and forearm Roots Figure 13.9 (a) 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 Figure 13.9 (c) Injuries Radial Nerve Ulnar Nerve Plexuses Lumbar plexus Arises from L1–L5 (some T12) Innervates thigh, abdominal wall, external genitalia, leg & foot Femoral nerve Innervates quadriceps, skin of anterior thigh & medial surface of leg Obturator nerve Passes through obturator foramen Innervates adductor muscles Ventral rami Ventral rami: Iliohypogastric L1 Ilioinguinal Femoral Iliohypogastric Ilioinguinal L2 Genitofemoral L3 Lateral femoral cutaneous Obturator L4 Femoral Lumbosacral trunk L5 Lateral femoral cutaneous Obturator Anterior femoral cutaneous Saphenous (a) Ventral rami and major branches of the lumbar plexus (b) Distribution of the major nerves from the lumbar plexus to the lower limb Figure 13.10 Plexuses Sacral plexus Arises from L4–S4 Serves the buttock, lower limb, pelvic structures & perineum Sciatic nerve Longest and thickest nerve of the body Innervates • Muscles of the leg and foot • Skin on the leg and foot Ventral rami Ventral rami: L4 Superior gluteal Lumbosacral trunk Inferior gluteal Common fibular Tibial Posterior femoral cutaneous Pudendal Sciatic L5 S1 S2 S3 S4 S5 Co1 Ventral rami and major branches of the sacral plexus 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 Figure 13.11 (b)
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