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Transcript
The Peripheral Nervous System Liam Chen, MD/PhD 9/22/2014 The Peripheral Nervous System • Nervous structures outside the brain and spinal cord • Nerves allow the CNS to receive information and take action • Functional components of the PNS • Sensory inputs and motor outputs categorized as somatic or visceral • Sensory inputs also classified as general or special Sensory Input and Motor Output • • • Sensory (afferent) signals picked up by sensor receptors, carried by nerve fibers of PNS to the CNS Motor (efferent) signals are carried away from the CNS, innervate muscles and glands Divided according to region they serve • • • Somatic body region Visceral body region Results in four main subdivisions • • • • Somatic sensory Visceral sensory Somatic motor Visceral motor Types of Sensory and Motor Information Sensory • General somatic senses – include touch, pain, temperature, vibration, pressure. • Proprioceptive senses – detect stretch in tendons and muscle provide information on body position, orientation and movement of body in space • Special Senses - hearing, balance, vision, olfaction (smell), gustation (taste) Sensory Receptors • Free nerve endings (pain • • • • and temp) Merkel discs (light touch) Meissner’s corpuscles (light touch) Ruffini’s corpusucles (deep pressure and stretch) Pacinian corpuscles (deep pressure, vibration) Motor • General somatic motor • Signals contraction of skeletal muscles • Under our voluntary control • Visceral motor • Makes up autonomic nervous system (ANS) • Regulates the contraction of smooth and cardiac muscle, controls function of visceral organs • ANS has two divisions • Parasympathetic • Sympathetic Sympathetic Division Organization • Preganglionic neurons in segments T1 to L2 • Ganglia near the vertebral column • Preganglionic fibers to adrenal medullae • Epinephrine (adrenalin) into blood stream Parasympathetic Division Organization • Preganglionic neurons in brain stem and sacral spinal segment • Ganglionic neurons (peripheral ganglia) in or near target organ • Sacral fibers form pelvic nerves Comparison of somatic and autonomic nervous systems Central nervous system Peripheral nervous system Effector organs Acetylcholine Somatic nervous system Skeletal muscle Acetylcholine Sympathetic division Autonomic nervous system Norepinephrine Smooth muscle (e.g., in gut) Ganglion Acetylcholine Epinephrine and norepinephrine Blood vessel Glands Adrenal medulla Acetylcholine Parasympathetic division Human Anatomy and Physiology, 7e by Elaine Marieb & Katja Hoehn Cardiac muscle Ganglion Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings. The 12 Pairs of Cranial Nerves Most cranial nerves have their nuclei in the brain stem 15 Olfactory Nerves (I) • Sensory nerves of smell 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 Table 14.3 (1 of 12) Optic Nerve (II) • Sensory nerve of vision 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 Table 14.3 (2 of 12) Oculomotor Nerve (III) • Innervates four of the extrinsic eye muscles • Parasympathetic 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 Table 14.3 (3 of 12) Oculomoter Nerve Compression Oculomoter Nerve Compression Oculomoter Nerve Compression RE is down and out with complete ptosis and a fixed, dilated pupil. Trochlear Nerve (IV) • Innervates the superior oblique muscle 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 Table 14.3 (4 of 12) Trigeminal Nerve (V) • • Provides sensory innervation to the face Motor innervation to chewing muscles 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 Abducens Nerve (VI) • Abducts the eyeball – innervates lateral rectus muscle 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 Table 14.3 (6 of 12) • • Facial Nerve (VII) Innervates muscles of facial expression Parasympathetic Facial nerve (VII) Vestibulocochlear nerve (VIII) Glossopharyngeal nerve (IX) Vagus nerve (X) Accessory nerve (XI) Hypoglossal nerve (XII) Table 14.3 (7 of 12) Vestibulocochlear Nerve (VIII) • Sensory nerve of hearing and balance Facial nerve (VII) Vestibulocochlear nerve (VIII) Glossopharyngeal nerve (IX) Vagus nerve (X) Accessory nerve (XI) Hypoglossal nerve (XII) Table 14.3 (8 of 12) Glossopharyngeal Nerve (IX) • Innervates structures of the tongue and pharynx • Parasympathetic Facial nerve (VII) Vestibulocochlear nerve (VIII) Glossopharyngeal nerve (IX) Vagus nerve (X) Accessory nerve (XI) Hypoglossal nerve (XII) Table 14.3 (9 of 12) Vagus Nerve (X) • A mixed sensory and motor nerve - “Wanders” into thorax and abdomen • Parasympathetic Facial nerve (VII) Vestibulocochlear nerve (VIII) Glossopharyngeal nerve (IX) Vagus nerve (X) Accessory nerve (XI) Hypoglossal nerve (XII) Table 14.3 (10 of 12) Accessory Nerve (XI) • Innervates trapezius muscle Facial nerve (VII) Vestibulocochlear nerve (VIII) Glossopharyngeal nerve (IX) Vagus nerve (X) Accessory nerve (XI) Hypoglossal nerve (XII) Table 14.3 (11 of 12) Hypoglossal Nerve (XII) • Runs inferior to the tongue - innervates the tongue muscles Facial nerve (VII) Vestibulocochlear nerve (VIII) Glossopharyngeal nerve (IX) Vagus nerve (X) Accessory nerve (XI) Hypoglossal nerve (XII) Table 14.3 (12 of 12) Spinal Nerves • • • 31 pairs – contain thousands of nerve fibers Connect to the spinal cord Named for point of issue from the spinal cord • 8 pairs of cervical nerves (C1– C8) • 12 pairs of thoracic nerves (T1– T12) • 5 pairs of lumbar nerves (L1–L5) • 5 pairs of sacral nerves (S1–S5) • 1 pair of coccygeal nerves (Co1) Spinal Nerves • Connect to the spinal cord by the dorsal root and ventral root • • • • • Dorsal root – contains sensory fibers Dorsal root ganglion – of afferent cell bodies Ventral root – contains motor fibers arising from anterior gray column Branch into dorsal ramus and ventral ramus both contain sensory and motor fibers Rami communicantes connect to the base of the ventral ramus and lead to the sympathetic chain ganglia Structure of a nerve Axon Blood vessels Perineurium Myelin sheath Endoneurium Perineurium Epineurium Fascicle Fascicle Blood vessels (a) Endoneurium Nerve fibers (b) Human Anatomy and Physiology, 7e by Elaine Marieb & Katja Hoehn Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings. Nerves • Nerves – cablelike organs in the • PNS Consists of numerous axons wrapped in connective tissue • • Endoneurium – layer of delicate connective tissue surrounding the axon Perineurium – connective tissue wrapping surrounding a nerve fascicle • Nerve fascicles – groups of axons bound into bundles • Epineurium – whole nerve is surrounded by tough fibrous sheath • Axon is surrounded by Schwann cells The motor unit: neuron and muscle fibers Muscle fiber types (determined by axons) • Type 1 • • • - slow twitch (postural), oxidative, fatigue-resistant - rich in mitochondria, lipids, and oxidative enzymes - dark on NADH, light on ATPase 9.4 • Type 2 • • • • - fast twitch, glycolytic, fatigable - rich in glycogen, glycolytic enzymes (phosphorylase) - light on NADH, dark on ATPase 9.4 ATPase 9.4, type 2 dark Acute denervation: esterase stain • Denervated fibers • dark and often angulated Scattered atrophic fibers in H&E can be nonspecific Chronic denervation: type grouping Questions? 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