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The Nervous System P N S C R A N I A L N E R V E S S P I N A L N E R V E S
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 Perineurium Epineurium Axon Myelin sheath Fascicle Blood vessels (b) Figure 13.3b
Cranial Nerves Twelve pairs of nerves associated with the brain Most are mixed in function; two pairs are purely sensory Each nerve is identified by a number (I through XII) and a 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) (a) 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 Figure 13.5 (a)
Cranial nerves I VI Sensory function Motor function PS* fibers I Olfactory Yes (smell) No No II Optic Yes (vision) No No III Oculomotor No Yes Yes IV Trochlear No Yes No V Trigeminal Yes (general sensation) Yes No VI Abducens No Yes No Cranial nerves VII XII Sensory function Motor function PS* fibers VII Facial Yes (taste) Yes Yes VIII Vestibulocochlear Yes (hearing and balance) Some No IX Glossopharyngeal Yes (taste) Yes Yes X Vagus Yes (taste) Yes Yes XI Accessory No Yes No XII Hypoglossal No Yes No (b) *PS = parasympathetic Figure 13.5 (b)
Table 13.2
Table 13.2
Table 13.2
Table 13.2
Table 13.2
Table 13.2
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 )
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 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
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
Spinal Nerves: Rami Each spinal nerve branches into mixed rami Dorsal ramus Ventral ramus Meningeal branch Rami communicantes (autonomic pathways) join to the ventral rami in the thoracic region
Dorsal root ganglion Dorsal ramus of spinal nerve Ventral ramus of spinal nerve Spinal nerve Rami communicantes Sympathetic trunk ganglion Gray matter White matter Ventral root Dorsal root Dorsal and ventral rootlets of spinal nerve 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)
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)
Spinal Nerves: 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
Figure 13.12 C2 C3 C4 C5 T1 T2 T2 T3 T4 T5 C6 C8 C7 C7 C6 T6 T7 T8 T9 T10 T11 T12 L1 S2 S3 L1 L2 L3 L4 L5 L2 L3 L4 L5 S1 C5 C6 C8 T2 C5 C6 S1 Anterior view C2 C3 C4 C5 C6 C7 C8 C8 C8 C7 C7 T1 T2 T3 T4 T5 T6 T7 T8 T9 T10 T11 T12 L1 L2 L3 S1 (b) Posterior view L5 S2 S1 S1 S3 S2 S1 S2 S4 S5 L5 L5 L4 L5 L5 L4 C6 C6 C5 L4 L3 L2 L1 L4
Spinal Nerves: Dorsal Ramus Innervates deep back muscles and posterior surface 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)
Spinal Nerves: Ventral Ramus & Plexuses All ventral rami form interlacing nerve networks 4 plexuses cervical, brachial, lumbar, and sacral Exception: ventral rami of T 2 T 12 Do not form a plexus, instead form intercostal nerves
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 Lumbar nerves L 1 L 5 Sacral nerves S 1 S 5 Coccygeal nerve Co 1 Figure 13.6
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 )
Ventral rami Segmental branches Hypoglossal nerve (XII) Lesser occipital nerve Greater auricular nerve Transverse cervical nerve Ansa cervicalis Accessory nerve (XI) Phrenic nerve Supraclavicular nerves Ventral rami: C 1 C 2 C 3 C 4 C 5 Figure 13.8
Brachial Plexus Formed by ventral rami of C 4 T 1 Gives rise to the nerves that innervate the upper limb Median Ulnar Axillary Radial Musculocutaneous
Roots (ventral rami): Cords Posterior divisions Lateral Posterior Medial Axillary Musculocutaneous Radial Median Ulnar Dorsal scapular Nerve to subclavius Suprascapular (a) Roots (rami C 5 T 1 ), trunks, divisions, and cords C 4 C 5 C 6 C 7 C 8 T 1 Upper Middle Lower Trunks Long thoracic Medial pectoral Lateral pectoral Upper subscapular Lower subscapular Thoracodorsal Medial cutaneous nerves of the arm and forearm Anterior divisions Posterior divisions Trunks 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
Lumbar Plexus Arises from L 1 L 5 (some T 12 ) Innervates the thigh, abdominal wall, external genitalia, leg, and foot Femoral nerve Innervates quadriceps and skin of anterior thigh and medial surface of leg Obturator nerve Passes through obturator foramen Innervates adductor muscles
Ventral rami Iliohypogastric Ilioinguinal Genitofemoral Lateral femoral cutaneous Obturator Femoral Lumbosacral trunk Ventral rami: L 1 L 2 L 3 L 4 L 5 Iliohypogastric Ilioinguinal Femoral 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
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 muscles and skin in the leg and foot
Ventral rami 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 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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