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

3. Functional Organization of the PNS

4. 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

5. Structural Organization of PNS in Region of a Spinal Nerve

6. Peripheral Endings Afferent: Sensory Receptors Efferent: Somatic Motor
Efferent: Autonomic Nervous System

7. Peripheral Sensory Receptors
Afferent: Sensory
Peripheral Sensory Receptors
Structures that pick up sensory stimuli
Initiate signals in sensory axons

8. Peripheral Sensory Receptors
Two main categories of sensory receptors
Special nerve endings of sensory neurons
Monitor general sensory information
Independent receptor cells – specialized epithelial cells or small neurons
Monitor most types of special sensory information

9. Sensory Receptors

10. Peripheral Sensory Receptors
Sensory receptors also classified according to:
Location
Type of stimulus detected
Structure

11. 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
Interoceptors – (visceroceptors) receive stimuli from internal viscera
Monitor a variety of stimuli
Proprioceptors – monitor degree of stretch
Located in musculoskeletal organs

12. Classification by Modality
Mechanoreceptors – respond to mechanical forces
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

13. Classification by Structure
General sensory receptors
Widely distributed
Nerve endings of sensory neurons monitor:
Touch, pressure, vibration, stretch
Pain, temperature, proprioception
Divided into two groups
Free nerve endings
Encapsulated nerve endings

14. Free Nerve Endings
Abundant in epithelia and underlying connective tissue
Respond to pain and temperature
Monitor affective senses
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

15. Unencapsulated Nerve Endings

16. Encapsulated Nerve Endings
Consist of one or more end fibers of sensory neurons
Enclosed in connective tissue
Mechanoreceptors
Include four main types

17. Encapsulated Nerve Endings
Encapsulated nerve endings: dendrites with special supporting structures (mechanoreceptors and proprioceptors)

18. Encapsulated Nerve Endings
Meissner’s corpuscles
Pacinian corpuscles
Ruffini’s corpuscles
Proprioceptors

19. Encapsulated Receptors

20. Proprioceptors Monitor stretch in locomotory organs
Three types of proprioceptors

21. 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

22. Proprioceptors

23. Structure of Receptors in Skin

24. Somatic Efferent: Innervation of Skeletal Muscles

25. Innervation of Skeletal Muscle
Motor axons innervate skeletal muscles
Neuromuscular junctions (motor end plates)
Similar to synapses between neurons
Acetylcholine diffuses across the synaptic cleft
Binds with molecules on the sarcolemma
Motor axons branch to innervate muscle fibers

26. The Neuromuscular Junction

27. Innervation of Skeletal Muscle
Motor unit – a motor neuron and all the muscle fibers it innervates

28. Efferent: Autonomic Nervous System

29. Innervation of Visceral Muscle and Glands
Simpler than neuromuscular junctions of skeletal muscle
Near the smooth muscle or gland it innervates
Visceral motor axon swells into a row of varicosities
Visceral motor responses
Slower than somatic motor reflexes

30. Innervation of Smooth Muscle

31. Cranial Nerves

32. 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

33. The 12 Pairs of Cranial Nerves

34. CN I: Olfactory Nerves Sensory nerves of smell Sense of smell
Damage causes impaired sense of smell

35. CN II: Optic Nerve Sensory nerve of vision Provides vision
Damage causes blindness in visual field

36. CN III: Oculomotor Nerve
Innervates four of the extrinsic eye muscles
Somatic and Autonomic motor function
Eye movement (Superior, inferior, medial rectus muscles and inferior oblique muscle), opening of eyelid (levator palpebrae superioris), constriction of pupil (circular muscle), focusing (ciliary muscle and accomodation)
Damage causes drooping eyelid, dilated pupil, double vision, difficulty focusing and inability to move eye in certain directions

37. CN IV: Trochlear Nerve Innervates an extrinsic eye muscle
Eye movement (superior oblique muscle)
Damage causes double vision and inability to rotate eye inferolaterally

38. CN V: Trigeminal Nerve Provides sensory innervation to the face
Motor innervation to chewing muscles
Ophthalmic branch – sensations from nasal cavity, skin of forehead, upper eyelid, eyebrow, nose
Maxillary branch – sensations from lower eyelid, upper lips and gums, teeth of the maxilla, cheek, nose, palate, pharynx
Mandibular branch – sensations from teeth of the mandible, lower gums and lips, palate, tongue. Motor function of temporalis and masseter muscles.
Damage produces loss of sensation and impaired chewing

39. Trigeminal Nerve

40. CN VI: Abducens Nerve Abducts the eyeball
Provides eye movement (lateral rectus m.)
Damage results in inability to rotate eye laterally and at rest eye rotates medially

41. CN VII: Facial Nerve Innervates muscles of facial expression
Sensory innervation of face
Taste
Somatic Motor - facial expressions
Autonomic Motor - salivary and lacrimal glands, mucous membranes of nasal and palatine mucosa
Special Sensory - taste on anterior 2/3’s of tongue
Damage produces sagging facial muscles and disturbed sense of taste (no sweet and salty)

42. Branches of Facial Nerve
Clinical test: Test anterior 2/3’s of tongue with substances such as sugar, salt, vinegar, and quinine; test response of tear glands to ammonia fumes; test motor functions by asking subject to close eyes, smile, whistle, frown, raise eyebrows, etc.

43. CN VIII: Vestibulocochlear Nerve
Sensory nerve of hearing and balance
Special Sensory
Provides hearing (cochlear branch) and sense of balance (vestibular branch)
Damage produces deafness, dizziness, nausea, loss of balance and nystagmus

44. CN IX: Glossopharyngeal Nerve
Sensory and motor innervation of structures of the tongue and pharynx
Taste
Somatic motor – Swallowing and voice production via pharyngeal muscles
Autonomic motor - salivation, gagging, control of BP and respiration
Sensations from posterior 1/3 of tongue including taste
Sensations from baroreceptors and chemoreceptors
Damage results in loss of bitter and sour taste and impaired swallowing, blood pressure anomalies (with CN X).

45. CN X: Vagus Nerve A mixed sensory and motor nerve
Main parasympathetic nerve
“Wanders” into thorax and abdomen

46. Vagus Nerve X
Sensations from skin at back of ear, external acoustic meatus, part of tympanic membrane, larynx, trachea, espophagus, thoracic and abdominal viscera
Sensations from bararoceptors and chemoreceptors
Special sensory – taste from epiglottis and pharynx
Somatic motor – Swallowing and voice production via pharyngeal muscles
Autonomic motor – smooth muscle of abdominal viscera, visceral glands secretions, relaxation of airways, and normal or decreased heart rate.
Damage causes hoarseness or loss of voice, impaired swallowing, GI dysfunction, blood pressure anomalies (with CN IX), fatal if both are cut

47. CN XI: Accessory Nerve An accessory part of the vagus nerve
Somatic motor function of pharynx, larynx, neck muscles
Swallowing, head, neck and shoulder movement via trapezius and sternocleidomastoid and pharyngeal muscles
Damage causes impaired head, neck, shoulder movement

48. CN XII: Hypoglossal Nerve
Runs inferior to the tongue
Innervates the
tongue muscles
Tongue movements for speech, food manipulation and swallowing
If both are damaged – can’t protrude tongue
If one side is damaged – tongue deviates towards injured side

49. Cranial Nerve Disorders
Trigeminal neuralgia (tic douloureux)
recurring episodes of intense stabbing pain in trigeminal nerve area (near mouth or nose)
pain triggered by touch, drinking, washing face
treatment may require cutting nerve
Bell’s palsy
disorder of facial nerve causes paralysis of facial muscles on one side
may appear abruptly with full recovery within 3-5 weeks

50. Spinal Nerves

51. 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)

52. Spinal Nerves Posterior View

53. 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 (cell bodies in gray matter of spinal cord – no ganglia)

54. Spinal Nerves Branch into dorsal ramus and ventral ramus
Rami communicantes connect to the base of the ventral ramus
Lead to the sympathetic chain ganglia (gray and white ramus)
Dorsal and ventral rami contain sensory and motor fibers

55. 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

56. Map of Dermatomes – Anterior View

57. Map of Dermatomes – Posterior View

58. Disorders of the PNS: Shingles
Shingles (herpes zoster)
Viral infection
Stems from childhood chicken pox
Often brought on by stress
Mostly experienced by those over 50

59. Disorders of the PNS: Migraine Headache
Relates to sensory innervation of cerebral arteries
Arteries dilate
Compresses and irritates sensory nerve endings

60. Disorders of the PNS: Myasthenia Gravis
Progressive weakening of the skeletal muscles
An autoimmune disorder
Antibodies destroy acetylcholine receptors
Ptosis due to weakness of eyelid muscles