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The Peripheral Nervous System: Structure and Function

Explore the structure and function of the peripheral nervous system, including sensory receptors, nerve endings, and classification of stimuli. Learn about the different types of sensory receptors and their locations.

dwaynecooper
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The Peripheral Nervous System: Structure and Function

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  1. 14 PART 1 The PeripheralNervous System Pages 425-460

  2. The Peripheral Nervous System • The PNS • Is the nervous system outside the brain and spinal cord • Provides vital links to the body and outside world • Nerves allow the CNS to receive information and initiate action • Sensory inputs and motor outputs • Categorized as • Somatic or visceral • General or special

  3. Central nervous system (CNS) Peripheral nervous system (PNS) Sensory (afferent) division Motor (efferent) division Somatic sensory General: Touch, pain, pressure, vibration, temperature, and proprioception in skin, body wall, and limbs Visceral sensory General: Stretch, pain, temperature, chemical changes, and irritation in viscera; nausea and hunger Somatic nervous system Autonomic nervous system (ANS) Motor innervation of all skeletal muscles Motor innervation of smooth muscle, cardiac muscle, and glands Special: Hearing, equilibrium, vision Special: Taste, smell Sympathetic division Parasympathetic division Functional Organization of the PNS Figure 14.1

  4. Basic Structural Components of the PNS • Sensory receptors—pick up stimuli from inside or outside the body • Nerves and ganglia • Nerves—bundles of peripheral axons • Ganglia—clusters of peripheral neuronal cell bodies • Motor endings—axon terminals of motor neurons • Innervate effectors (muscle fibers and glands)

  5. Dorsal root (sensory) Dorsal horn (interneurons) Dorsal root ganglion SS Somatic sensory neuron VS VM Visceral sensory neuron SM Visceral motor neuron Ventral horn (motor neurons) Somatic motor neuron Spinal nerve Ventral root (motor) Interneurons receiving input from somatic sensory neurons Interneurons receiving input from visceral sensory neurons Visceral motor (autonomic) neurons Somatic motor neurons Figure 13.27

  6. Peripheral Sensory Receptors • Structures that pick up sensory stimuli • Initiate signals in sensory axons • Two main categories of sensory receptors • Free nerve endings of sensory neurons • Monitor general sensory information • Complete receptor cells—specialized epithelial cells or small neurons • Monitor most types of special sensory information

  7. Classification by Location • Exteroceptors—sensitive to stimuli arising from outside the body • Located at or near body surfaces • Include receptors for touch, pressure, pain, and temperature

  8. Classification by Location • Interoceptors—receive stimuli from internal viscera • Located in digestive tube, bladder, and lungs • Monitor a variety of stimuli • Changes in chemical concentration • Taste stimuli • Stretching of tissues • Temperature

  9. Classification by Location • Proprioceptors • Located in skeletal muscles, tendons, joints, and ligaments • Monitor degree of stretch • Send inputs on body movement to the CNS

  10. Classification by Stimulus Detected • Mechanoreceptors—respond to mechanical forces • Touch, pressure, stretch, vibration, and itch • Baroreceptors monitor blood pressure • Thermoreceptors—respond to temperature changes • Chemoreceptors • Respond to chemicals in solution • Photoreceptors—respond to light • Located in the eye • Nociceptors • Respond to harmful stimuli that result in pain

  11. Classification by Structure • General sensory receptors are • Divided into two groups • Free nerve endings • Encapsulated nerve endings • Abundant in epithelia and underlying connective tissue • Respond to pain and temperature • Monitor affective senses Free Nerve Endings

  12. Free Nerve Endings • Two specialized types of free nerve endings • Epithelial tactile complexes (Merkel discs) • Consist of tactile epithelial cell innervated by sensory nerve ending • Slowly adapting receptors for light touch • Hair follicle receptors—wrap around hair follicles • Rapidly adapting receptors

  13. Unencapsulated Nerve Endings Table 14.1 (1 of 4)

  14. Encapsulated Nerve Endings • Consist of one or more end fibers of sensory neurons • Enclosed in connective tissue • Mechanoreceptors • Include four main types • Tactile (Meissner’s) corpuscles • Lamellar (Pacinian) corpuscles • Bulbous corpuscles (Ruffini endings) • Proprioceptors

  15. Encapsulated Nerve Endings • Tactile (Meissner’s) corpuscles • Spiraling nerve ending surrounded by Schwann cells • Occur in the dermal papillae • Rapidly adapting receptors for discriminative touch • Occur in sensitive, hairless areas of the skin

  16. Encapsulated Nerve Endings • Lamellar Corpuscles • Single nerve ending surrounded by layers of flattened Schwann cells • Occur in the hypodermis • Sensitive to deep pressure—rapidly adapting receptors • Bulbous Corpuscles • Located in the dermis and respond to pressure • Monitor continuous pressure on the skin—adapt slowly

  17. Lamellar Corpuscles and Bulbous Corpuscles Table 14.1 (3 of 4)

  18. Three Types of Proprioceptors • Muscle spindles—measure the changing length of a muscle • Imbedded in the perimysium between muscle fascicles • Golgi tendon organs—located near the muscle-tendon junction • Monitor tension within tendons • Joint kinesthetic receptors • Sensory nerve endings within the joint capsules

  19. Proprioceptors Table 14.1 (4 of 4)

  20. Secondary sensory endings (type II fiber)  Efferent (motor) fiber to muscle spindle  Efferent (motor) fiber to extrafusal muscle fibers Primary sensory endings (type Ia fiber) Extrafusal muscle fiber Muscle spindle Intrafusal muscle fibers Connective tissue capsule Sensory fiber Tendon organ Tendon

  21. Cranial Nerves • Attach to the brain and pass through foramina of the skull • Numbered from I–XII • Cranial nerves I and II attach to the forebrain • All others attach to the brain stem • Primarily serve head and neck structures • The vagus nerve (X) is the only cranial nerve that extends into the abdomen

  22. Filaments of olfactory nerve (I) Frontal lobe Olfactory bulb Olfactory tract Optic nerve (II) Temporal lobe Optic chiasma Optic tract Oculomotor nerve (III) Infundibulum Trochlear nerve (IV) Facial nerve (VII) Vestibulocochlear nerve (VIII) Trigeminal nerve (V) Abducens nerve (VI) Glossopharyngeal nerve (IX) Vagus nerve (X) Cerebellum Accessory nerve (XI) Medulla oblongata Hypoglossal nerve (XII) (a) The Cranial Nerves Figure 14.4a

  23. Figure 14.4b The cranial nerves. Olfactory bulbwith filaments ofolfactory nerve (I) Frontal lobe Olfactory tract Optic nerve (II) Optic chiasma Optic tract Temporal lobe Oculomotornerve (III) Facial nerve (VII) Trochlearnerve (IV) Vestibulocochlearnerve (VIII) Trigeminalnerve (V) Abducensnerve (VI) Glossopharyngealnerve (IX) Cerebellum Vagus nerve (X) Accessory nerve (XI) Medulla oblongata Hypoglossal nerve (XII)

  24. Cranial nerves Sensory function Motor function Somatic sensory (SS) Visceral sensory (VS) Somatic motor (SM) Visceral motor: parasympathetic (VM) I Olfactory Smell II Optic Vision III Oculomotor SM VM IV Trochlear SM General V Trigeminal SM VI Abducens SM (b) The Cranial Nerves Figure 14.4c (1 of 2)

  25. Cranial nerves Sensory function Motor function Somatic sensory (SS) Visceral sensory (VS) Somatic motor (SM) Visceral motor: parasympathetic (VM) VII Facial General General; taste SM VM VIII Vestibulocochlear Hearing; equilibrium Some IX Glossopharyngeal General General; taste SM VM X Vagus General General; taste SM VM XI Accessory SM XII Hypoglossal SM (b) The Cranial Nerves Figure 14.4c (2 of 2)

  26. Location of Cell Bodies

  27. Solitary nucleus Hypoglossal nucleus (XII) Fourth ventricle Dorsal motor nucleus of vagus (X) Vestibular nuclear complex (VIII) Choroid plexus Inferior cerebellar peduncle Cochlear nuclei (VIII) Lateral nuclear group Medial nuclear group Nucleus ambiguus Reticular formation Raphe nucleus Inferior olivary nucleus Medial lemniscus Pyramid (c) Medulla oblongata

  28. Location of Cell Bodies

  29. Dorsal root (sensory) Dorsal horn (interneurons) Dorsal root ganglion SS Somatic sensory neuron VS VM Visceral sensory neuron SM Visceral motor neuron Ventral horn (motor neurons) Somatic motor neuron Spinal nerve Ventral root (motor) Interneurons receiving input from somatic sensory neurons Interneurons receiving input from visceral sensory neurons Visceral motor (autonomic) neurons Somatic motor neurons

  30. Table 14.2 Cranial Nerves (1 of 18)

  31. Table 14.2 Cranial Nerves (2 of 18)

  32. Table 14.2 Cranial Nerves (3 of 18)

  33. Table 14.2 Cranial Nerves (4 of 18)

  34. Table 14.2 Cranial Nerves (5 of 18)

  35. Table 14.2 Cranial Nerves (7 of 18)

  36. The Trigeminal Nerves • Largest of the cranial nerves • Has three divisions • Ophthalmic division (V1) • Maxillary division (V2) • Mandibular division (V3) • Cell bodies of sensory neurons located in the trigeminal ganglion • Mandibular division contains motor fibers that innervate the chewing muscles

  37. Table 14.2 Cranial Nerves (8 of 18)

  38. Table 14.2 Cranial Nerves (9 of 18)

  39. Table 14.2 Cranial Nerves (10 of 18)

  40. Table 14.2 Cranial Nerves (11 of 18)

  41. The Facial Nerves • Mixed nerves • Chief motor nerves of face • Has five major branches • Temporal, zygomatic, buccal, mandibular & cervical • Somatic motor impulses to facial skeletal muscles & proprioceptor signals from muscles to pons • Autonomic motor impulses to lacrimal gland & salivary glands • Special sensory impulses from taste buds and general sensory impulses from skin on ear

  42. Table 14.2 Cranial Nerves (12 of 18)

  43. Table 14.2 Cranial Nerves (13 of 18)

  44. Table 14.2 Cranial Nerves (14 of 18)

  45. Table 14.2 Cranial Nerves (15 of 18)

  46. Table 14.2 Cranial Nerves (16 of 18)

  47. Table 14.2 Cranial Nerves (17 of 18)

  48. XI The Accessory Nerves • Unique among cranial nerves • Accessory nerves are formed from ventral rootlets of the spinal cord • Do not arise from the brainstem • Motor nerves • Somatic motor fibers to trapezius and sternocleidomastoid muscles

  49. Table 14.2 Cranial Nerves (18 of 18)

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