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1/17/2016 Peripheral Nervous System (PNS) • All neural structures outside the brain and spinal cord – Sensory receptors – Peripheral nerves and associated ganglia – Motor neuron endings – Constitutes a pathway between CNS and outlying structures – 12 pairs of cranial nerves – 31 pairs of spinal nerves The Nervous System Cranial and spinal Nerves Axon Endoneurium Myelin sheath Perineurium Epineurium Central nervous system (CNS) Peripheral nervous system (PNS) Sensory (afferent) division Fascicle Motor (efferent) division Blood vessels Somatic nervous system Autonomic nervous system (ANS) Sympathetic division Parasympathetic division (b) Figure 13.3b Figure 13.1 Cranial Nerves Frontal lobe • 12 pairs of nerves – Associated with the brain • Do not decussate – May continue in tracts that do – Typically see ipsilateral functional deficits with brain injury • Function may be sensory, motor, or both – Most are at least partially mixed • Each nerve is identified by… – Number (I through XII) – Name 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) 1 1/17/2016 Cranial nerves I – VI Sensory function Motor function PS* fibers I Olfactory Yes (smell) No No II Optic III Oculomotor Yes (vision) No No Yes No Yes IV Trochlear V Trigeminal No Yes (general sensation) Yes Yes No No Yes No VI Abducens Cranial nerves VII – XII VII Facial VIII Vestibulocochlear Sensory function Motor function • MANY mnemonics to help you remember name, order, and function – Google at your own risk • A few possibilities… PS* fibers Yes (taste) Yes (hearing and balance) Yes Some Yes No IX Glossopharyngeal Yes (taste) Yes Yes X Vagus Yes (taste) Yes Yes No No Yes Yes No No XI Accessory XII Hypoglossal (b) No Cranial Nerves *PS = parasympathetic Figure 13.5 (b) Table 13.2 Loss of function casues ptosis, external strabismus (“down and out” ) Trochlear Nerve Palsy 2 1/17/2016 Testing function Trigeminal neuralgia Loss of function causes internal strabismus Table 13.2 Vestibulocochlear Nerve Test Table 13.2 3 1/17/2016 Accessory Nerve Testing Table 13.2 Table 13.2 Functions of the cranial nerves Hypoglossal nerve testing Spinal Nerves Cervical plexus Brachial plexus • 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 enlargement Intercostal nerves Cervical nerves C1 – C8 Note: only 7 cervical vertebrae Thoracic nerves T1 – T12 Lumbar enlargement Lumbar plexus Sacral plexus Cauda equina Lumbar nerves L1 – L5 Sacral nerves S1 – S5 Coccygeal nerve Co1 Figure 13.6 4 1/17/2016 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 • Dorsal and ventral roots unite to form spinal nerves – Emerge from vertebral column via the intervertebral foramina Snack at 1AM Coccygeal (1) Spinal Nerve Organization Afferent Dorsal root (sensory) Dorsal root ganglion Dorsal horn (interneurons) Somatic sensory neuron • Rami – Each spinal nerve branches into mixed rami Visceral sensory neuron • Dorsal ramus • Ventral ramus Visceral motor neuron – Rami communicantes branch off of ventral ramus – Involved in ANS signaling pathways Spinal nerve Ventral root (motor) Somatic motor neuron Ventral horn (motor neurons) • Meningeal branch – Reenters the vertebral canal and innervates the meninges and blood vessels within Interneurons receiving input from somatic sensory neurons Efferent Interneurons receiving input from visceral sensory neurons Visceral motor (autonomic) neurons Somatic motor neurons Figure 12.32 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) 5 1/17/2016 Spinal Nerve Organization Dorsal ramus Ventral ramus • Dorsal ramus Spinal nerve – Innervates Rami communicantes • Deep back muscles • Posterior surface of trunk (skin and muscle) Intercostal nerve Dorsal root ganglion Dorsal root Ventral root Branches of intercostal nerve • Lateral cutaneous • Anterior cutaneous Sympathetic trunk ganglion • Ventral ramus – Innervates • Superficial back muscles • Limbs • Lateral and anterior surfaces of trunk (skin and muscle on side, chest, ribs, abdominal wall) Sternum (b) Cross section of thorax showing the main roots and branches of a spinal nerve. Figure 13.7 (b) Distribution of Spinal Nerves C2 C3 C4 C5 C6 C7 C8 T1 T2 T3 T4 T5 T6 T7 T8 T9 T10 C2 C3 C4 • 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 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 C8 L2 S1 L4 S3 S4 S5 C6 C7 S2 C6 C7 C8 C8 L2 S2 S2 S1 L1 L3 L5 L4 T11 T12 L1 L3 L5 C7 C6 L1 S1 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 Cervical plexus Brachial plexus • All ventral rami form interlacing nerve networks – 4 plexuses • Cervical, brachial, lumbar, and sacral – Fibers from the rami branch and become redistributed – Each nerve exiting the plexus has fibers from several spinal nerves • Advantage? Cervical enlargement Intercostal nerves Thoracic nerves T1 – T12 Lumbar enlargement Lumbar plexus • Exception: ventral rami of T2–T12 – Do not form a plexus – Form intercostal nerves Cervical nerves C1 – C8 Sacral plexus Cauda equina Lumbar nerves L1 – L5 Sacral nerves S1 – S5 Coccygeal nerve Co1 Figure 13.6 6 1/17/2016 Plexuses Ventral rami • Cervical plexus Segmental branches – Formed by ventral rami of C1–C4 – Innervates skin & muscles of the neck, ear, back of head, and shoulders Ventral rami: C1 Hypoglossal nerve (XII) Lesser occipital nerve Greater auricular nerve Transverse cervical nerve Ansa cervicalis C2 C3 C4 Accessory nerve (XI) C5 Phrenic nerve Supraclavicular nerves Figure 13.8 Plexuses Plexuses • Brachial plexus • Phrenic nerve – Major motor and sensory nerve of the diaphragm • Critical for breathing • • • • • – Receives fibers from C3–C5 • Therefore receives innervation from both the cervical plexus and the brachial plexus Roots (ventral rami): C4 C5 Dorsal scapular Nerve to subclavius Suprascapular Cords C7 Lateral C8 Posterior T1 Medial Axillary Musculocutaneous Radial Median Ulnar Axillary nerve Anterior divisions Posterior divisions Trunks Roots Upper Middle Trunks Lower Humerus Radial nerve Long thoracic Medial pectoral Lateral pectoral Upper subscapular Lower subscapular Thoracodorsal Medial cutaneous nerves of the arm and forearm (a) Roots (rami C5 – T1), trunks, divisions, and cords Posterior divisions Median Ulnar Axillary Radial Musculocutaneous C6 Posterior divisions Anterior divisions – Formed by ventral rami of C4– T1 – Gives rise to the nerves that innervate the upper limb Trunks Roots 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 (a) Figure 13.9 (c) 7 1/17/2016 Injuries • Radial nerve damage causes the fingers, wrist, or hand to be in the chronically flexed position – “Crutch paralysis” – caused when crutches are improperly adjusted – “Saturday night paralysis” – caused by falling asleep with the arm hanging over the armrest of a chair – “Honeymoon paralysis” – caused by someone else sleeping on and compressing the arm Injuries • Ulnar nerve is the largest nerve in the body that is not protected by muscle or bone • Injury is common – “Funny bone” – Weakness in flexion of the hand at wrist, inability to cross fingers – “Claw hand” at rest Injuries • Radial nerve damage causes the fingers, wrist, or hand to be in the chronically flexed position – Radial nerve is constantly pushed against the humerus, and cannot innervate extensor muscles – Improves quickly with therapy Injuries • Carpal tunnel – Caused when the median nerve is compressed as it travels through the wrist – Pain, numbness, tingling in the hand, forearm, and shoulder – Caused by anything that applies pressure to the median nerve • Esp. cumulative trauma caused by repetitive motion – If untreated may cause wasting on muscles at the base of the thumb Plexuses Ventral rami • Lumbar plexus – Arises from L1–L5 (some T12) – Innervates thigh, abdominal wall, external genitalia, leg & foot Ventral rami: Iliohypogastric L1 Ilioinguinal Femoral Iliohypogastric Ilioinguinal L2 Genitofemoral L3 Lateral femoral cutaneous Obturator L4 Femoral Lumbosacral trunk L5 • Femoral nerve – Innervates quadriceps, skin of anterior thigh & medial surface of leg – Functions in extending the knee; sensory function in skin on front and inner sides of thigh, shin, and arch of foot • Obturator nerve – Passes through obturator foramen – Innervates adductor muscles; sensory function in skin on medial aspect of thigh 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 8 1/17/2016 Plexuses Ventral rami Ventral rami: L4 • Sacral plexus Superior gluteal Lumbosacral trunk Inferior gluteal – Arises from L4–S4 – Serves the buttock, lower limb, pelvic structures & perineum – Gives rise to sciatic nerve • Longest and thickest nerve of the body • Innervates Common fibular Tibial Posterior femoral cutaneous Pudendal – Muscles of the leg and foot – Skin on the leg and foot 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) 9