1. The Peripheral Nervous System
PART 1
The Peripheral Nervous System

2. 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
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3. The Peripheral Nervous System
Autonomic nervous system (ANS)
General visceral motor part of the PNS
ANS has two divisions
Parasympathetic
Sympathetic
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4. Functional Organization of the PNS
Figure 14.1
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5. Basic Structural Components of the PNS
Sensory receptors – pick up stimuli from inside or outside the body
Motor endings – axon terminals of motor neurons
Innervate effectors (muscle fibers and glands)
Nerves and ganglia
Nerves – bundles of peripheral axons
Ganglia – clusters of peripheral neuronal cell bodies
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6. Basic Anatomical Scheme of the PNS in the Region of a Spinal Nerve
Figure 14.2
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7. Peripheral Sensory Receptors
Structures that pick up sensory stimuli
Initiate signals in sensory axons
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8. Peripheral Sensory Receptors
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
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9. Peripheral Sensory Receptors
Wednesday
Sensory receptors also classified according to
Location
Type of stimulus detected
Structure
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10. 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
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11. Classification by Location
Interoceptors – (visceroceptors) receive stimuli from internal viscera
Monitor a variety of stimuli
Proprioceptors – monitor degree of stretch
Located in musculoskeletal organs
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12. Classification by Stimulus Detected
Mechanoreceptors – respond to mechanical forces
Thermoreceptors – respond to temperature changes
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13. Classification by Stimulus Detected
Chemoreceptors
Respond to chemicals in solution
Photoreceptors – respond to light
Located in the eye
Nociceptors
Respond to harmful stimuli that result in pain
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14. Classification by Structure
General sensory receptors
Widely distributed
Nerve endings of sensory neurons monitor
Touch
Pressure
Vibration
Stretch
Pain
Temperature
Proprioception
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15. Classification by Structure
General sensory receptors are
Divided into two groups
Free nerve endings
Encapsulated nerve endings
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16. Abundant in epithelia and underlying connective tissue
Free Nerve Endings
Abundant in epithelia and underlying connective tissue
Respond to pain and temperature
Monitor affective senses
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17. Two specialized types of free nerve endings
Merkel discs – lie in the epidermis
Slowly adapting receptors for light touch
Hair follicle receptors – wrap around hair follicles
Rapidly adapting receptors
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18. Unencapsulated Nerve Endings
Table 14.1 (1 of 4)
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19. Encapsulated Nerve Endings
Consist of one or more end fibers of sensory neurons
Enclosed in connective tissue
Mechanoreceptors
Include four main types
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20. Encapsulated Nerve Endings
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
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21. Meissner’s Corpuscles
Table 14.1 (2 of 4)
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22. Encapsulated Nerve Endings
Pacinian corpuscles
Single nerve ending surrounded by layers of flattened Schwann cells
Occur in the hypodermis
Sensitive to deep pressure – rapidly adapting receptors
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23. Encapsulated Nerve Endings
Ruffini’s corpuscles
Located in the dermis and respond to pressure
Monitor continuous pressure on the skin – adapt slowly
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24. Pacinian Corpuscles and Ruffini’s Corpuscles
Table 14.1 (3 of 4)
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25. Encapsulated Nerve Endings
Proprioceptors
Monitor stretch in locomotory organs
Three types of proprioceptors
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26. 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
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27. Proprioceptors Table 14.1 (4 of 4)
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28. Structure of Proprioceptors
Figure 14.4
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29. The Peripheral Nervous System
PART 2
The Peripheral Nervous System

30. Attach to the brain and pass through foramina of the skull
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) extends into the abdomen
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31. The 12 Pairs of Cranial Nerves
Figure 14.5
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32. Sensory nerves of smell
Olfactory Nerves
Sensory nerves of smell
Table 14.3 (1 of 12)
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33. Sensory nerve of vision
Optic Nerve
Sensory nerve of vision
Table 14.3 (2 of 12)
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34. Innervates four of the extrinsic eye muscles
Oculomotor Nerve
Innervates four of the extrinsic eye muscles
Table 14.3 (3 of 12)
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35. Innervates the superior oblique muscle (an extrinsic eye muscle)
Trochlear Nerve
Innervates the superior oblique muscle (an extrinsic eye muscle)
Table 14.3 (4 of 12)
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36. Provides sensory innervation to the face
Trigeminal Nerve
Provides sensory innervation to the face
Motor innervation to chewing muscles
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37. Trigeminal Nerve Table 14.3 (5 of 12)
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38. The Peripheral Nervous System
PART 3
The Peripheral Nervous System

39. Abducts the eyeball – innervates lateral rectus muscle
Abducens Nerve
Abducts the eyeball – innervates lateral rectus muscle
Table 14.3 (6 of 12)
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40. Innervates muscles of facial expression
Facial Nerve
Innervates muscles of facial expression
Table 14.3 (7 of 12)
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41. Vestibulocochlear Nerve
Sensory nerve of hearing and balance
Table 14.3 (8 of 12)
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42. Glossopharyngeal Nerve
Innervates structures of the tongue and pharynx
Table 14.3 (9 of 12)
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43. A mixed sensory and motor nerve
Vagus Nerve
A mixed sensory and motor nerve
“Wanders” into thorax and abdomen
Parasympathetic innervation of organs
Table 14.3 (10 of 12)
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44. An accessory part of the vagus nerve
Accessory Nerve
An accessory part of the vagus nerve
Innervates trapezius muscle
Table 14.3 (11 of 12)
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45. Runs inferior to the tongue
Hypoglossal Nerve
Runs inferior to the tongue
Innervates the tongue muscles
Table 14.3 (12 of 12)
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46. The Peripheral Nervous System
PART 4
The Peripheral Nervous System

47. 31 pairs – contain thousands of nerve fibers
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)
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48. Spinal Nerves Posterior View
Figure 14.6
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49. Connect to the spinal cord by the dorsal root and ventral root
Spinal Nerves
Connect to the spinal cord by the dorsal root and ventral root
Dorsal root – contains sensory fibers
Cell bodies – located in the dorsal root ganglion
Ventral root – contains motor fibers arising from anterior gray column
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50. Branch into dorsal ramus and ventral ramus
Spinal Nerves
Branch into dorsal ramus and ventral ramus
Dorsal and ventral rami contain sensory and motor fibers
Rami communicantes connect to the base of the ventral ramus
Lead to the sympathetic chain ganglia (Chapter 15)
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51. Spinal Nerves
Figure 14.7a
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52. Innervation of the Back
Dorsal rami
Innervate back muscles
Follow a neat, segmented pattern
Innervate a horizontal strip of muscle and skin
In line with emergence point from the vertebral column
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53. Innervation of the Back
Figure 14.7b
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54. Innervation of the Anterior Thoracic and Abdominal Wall
Thoracic region
Ventral rami arranged in simple, segmented pattern
Intercostal nerves – supply intercostal muscles, skin, and abdominal wall
Each gives off lateral and anterior cutaneous branches
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55. Introduction to Nerve Plexuses
Nerve plexus – a network of nerves
Ventral rami (except T2 – T12)
Branch and join with one another
Form nerve plexuses
In cervical, brachial, lumbar, and sacral regions
Primarily serve the limbs
Fibers from ventral rami crisscross
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56. Formed by ventral rami of first four cervical nerves (cn 1 – 4)
The Cervical Plexus
Buried deep in the neck
Under the sternocleidomastoid muscle
Formed by ventral rami of first four cervical nerves (cn 1 – 4)
Most are cutaneous nerves
Some innervate muscles of the anterior neck
Phrenic nerve – the most important nerve of the cervical plexus
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57. The Brachial Plexus and Innervation of the Upper Limb
Brachial plexus lies in the neck and axilla
Formed by ventral rami of C5 – C8
Cords give rise to main nerves of the upper limb
Figure 14.9d
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58. Nerves from the Lateral and Medial Cords
Musculocutaneous – main branch of the lateral cord
Innervates the biceps brachii and brachialis
Median – originates from both lateral and medial cords
Innervates anterior forearm muscles and lateral palm
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59. Nerves from the Lateral and Medial Cords
Ulnar – branches from the medial cord
Innervates intrinsic hand muscles and skin of the medial hand
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60. Nerves from the Posterior Cord
Radial – continuation of the posterior cord
Largest branch of the brachial plexus
Innervates muscles of the posterior upper limb
Axillary
Innervates the deltoid and teres minor
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61. The Brachial Plexus Figure 14.9a
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62. Axillary and Radial Nerves
Figure 14.11
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63. The Peripheral Nervous System
PART 5
The Peripheral Nervous System

64. The Lumbar Plexus and Innervation of the Lower Limb
Arises from L1– L4
Smaller branches innervate the posterior abdominal wall and psoas muscle
Main branches innervate the anterior thigh
Femoral nerve – innervates anterior thigh muscles
Obturator nerve – innervates adductor muscles
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65. The Lumbar Plexus Figure 14.12a, b
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66. Arises from spinal nerves L4–S4 Caudal to the lumbar plexus
The Sacral Plexus
Arises from spinal nerves L4–S4
Caudal to the lumbar plexus
Often considered with the lumbar plexus
Lumbosacral plexus
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67. Innervation of the Lower Limb
Sciatic nerve – the largest nerve of the sacral plexus
Actually two nerves in one sheath
Tibial nerve – innervates most of the posterior lower limb
Common fibular (peroneal) nerve – innervates muscles of the anterolateral leg
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68. Innervation of the Lower Limb
Superior and inferior gluteal nerves
Innervate the gluteal muscles
Pudendal nerve
Innervates muscles of the perineum
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69. The Sacral Plexus Figure 14.13
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70. Innervation of the Skin: Dermatomes
Dermatome – an area of skin
Innervated by cutaneous branches of a single spinal nerve
Upper limb
Skin is supplied by nerves of the brachial plexus
Lower limb
Lumbar nerves – anterior surface
Sacral nerves – posterior surface
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71. Map of Dermatomes – Anterior View
Figure 14.14a
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72. Map of Dermatomes – Posterior View
Figure 14.14b
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73. Shingles (herpes zoster)
Disorders of the PNS
Shingles (herpes zoster)
Viral infection
Stems from childhood chicken pox
Often brought on by stress
Mostly experienced by those over 50
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74. Disorders of the PNS Migraine headache Myasthenia gravis
Relates to sensory innervation of cerebral arteries
Arteries dilate and compresses and irritate sensory nerve endings
Myasthenia gravis
Progressive weakening of the skeletal muscles
An autoimmune disorder
Antibodies destroy acetylcholine receptors
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75. The PNS Throughout Life
Spinal nerves form late in week 4
Each of the 31 pairs of spinal nerves
Sends motor fibers to an individual myotome
Sends sensory fibers to the overlying band of skin
During week 5 nerves reach the organs they innervate
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76. The PNS Throughout Life
Embryonic muscles migrate to new locations
Some skin dermatomes become displaced
Muscles and skin always retain their original nerve supply
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