1. The Peripheral Nervous
Chapter 13
The Peripheral Nervous
System (PNS)
Part A

2. Objectives:
Name sensory receptors according to their different classifications
Name/label cranial nerves and list their functions
Name the four major plexuses and their important associated nerves
Draw, label and describe the reflex arc
Describe in your own words reflex activity
Name sensory, motor pathways, pyramidal-extrapyramidal pathways, major ascending and descending tracts of the spinal cord

3. Peripheral Nervous System (PNS)
All neural structures outside the brain and spinal cord
Includes:
Sensory receptors
Peripheral nerves
Associated ganglia
Motor endings
Provides:
links to & from the external environment

4. PNS in the Nervous System
Figure 13.1

5. Sensory Receptors Specialized structures
Respond to changes in their environment
Environmental changes are called stimuli
Receptor activation results in graded potentials
Graded potentails trigger nerve impulses
Nerve impulses:
Are action potentials
Travel along afferent PNS fibers to the CNS
Sensation involves both:
Awareness of the stimulus, and
Perception of the stimulus(interpretation in the brain)

6. Receptor Classification: 1. Stimulus Type
Mechanoreceptors:
Respond to touch, pressure, vibration, stretch, and itch
Thermoreceptors:
Sensitive to changes in temperature
Photoreceptors:
Respond to light energy (e.g. retina)
Chemoreceptors:
Respond to chemicals (e.g. smell, taste, blood chemistry changes)
Nociceptors:
Respond to pain-causing stimuli

7. Receptor Class by: 2. Location
Exteroceptors:
Located:
Near the body surface
Respond to:
Stimuli arising outside the body
Include:
Touch, pressure, pain, and temperature (in skin)
Most receptors of the special sense organs (hearing, vision, equilibrium, taste, smell)

8. Receptor Class by Location contd.
Interoceptors:
Located:
In the internal viscera
In blood vessels
They respond to:
Stimuli arising within the body
Sensitive to:
Chemical changes, stretch, and temperature changes

9. Receptor Class by Location contd.
Proprioceptors:
Located in:
Skeletal muscles
Tendons, joints, & ligaments
Connective tissue coverings of bones & muscles
Respond to:
The degree of stretch of the organs they occupy
Constantly:
“Advise” the brain of one’s movements

10. Receptor Classification: 3. Structural Complexity
Simple (majority):
Modified dendritic endings of sensory neurons
Include:
Encapsulated receptors (connective tissue capsule)
Unencapsulated receptors (free ending)
Complex:
Are the actual sense organs:
Localized collections of cells
Associated with the special sense (vision, hering ..etc)

11. A nerve is a: Structure of a Nerve Cordlike organ of the PNS
Consists of parallel bundles of peripheral axons
Bundles are enclosed by:
Successive coverings of connective tissue
Axons make only a small fraction of the nerve bulk
The rest include:
Myelin, connective tissue coverings, blood vessels, and lymph vessels

12. Connective tissue coverings include:
Structure of a Nerve
Connective tissue coverings include:
Endoneurium
Loose connective tissue surrounding each axon
Perineurium:
Coarse connective tissue bundling fibers into fascicles
Epineurium:
Tough fibrous sheath enclosing all fascicles forming a nerve

13. Structure of a Nerve
Figure 13.3b

14. Classification of Nerves
Three types:
Sensory
Motor
Mixed
Sensory (afferent):
Carry impulse to the CNS
Motor (efferent):
Carry impulses from CNS
Mixed:
Contain both sensory and motor fibers
Carry impulses to and from CNS
Most common type of nerves

15. Break Slide
Sat Nov 10,’10

16. Peripheral Nerves Mixed nerves: The four types of mixed nerves are:
Often carry somatic and autonomic (visceral) impulses
The four types of mixed nerves are:
Somatic afferent
Somatic efferent
Visceral afferent
Visceral efferent
Peripheral nerves originate from:
The brain, and called cranial nerves
The spinal cord, and called spinal nerves

17. Cranial Nerves Twelve pairs of cranial nerves Arise from the brain
Have sensory, motor, or both functions
Each is identified by:
A number (Roman numerals “I through XII”), and
A specific name
Four (III, VII, IX, X) carry parasympathetic fibers that serve:
Visceral muscles
Glands

18. Cranial Nerves
Figure 13.5a

19. Figure 12.15a

20. Figure 12.15b

21. Summary of Function of Cranial Nerves
Figure 13.5b

22. Cranial Nerve I: Olfactory
Arises from the olfactory epithelium (in nasal mucosa)
Fibers terminate in the primary olfactory cortex
Functions solely:
By carrying sensory (afferent) impulses
For the sense of smell

23. Cranial Nerve I: Olfactory
Figure I from Table 13.2

24. Break Slide
Biol
Wed, Nov 7/12

25. Cranial Nerve II: Optic
Arises from the retina of the eye as the optic nerve
Optic nerves converge at the optic chiasma
Continue as optic tracts & synapse in the thalamus
The optic radiation fibers run to the visual cortex
Functions solely:
By carrying sensory afferent impulses
For vision

26. Cranial Nerve II: Optic
Figure II from Table 13.2

27. Cranial Nerve III: Oculomotor (Eye Mover)
Fibers extend from the ventral midbrain
They go to the eye muscles
Functions (mainly motor “somatic & parasympathetic”):
Raises the eyelid
Directs the eyeball by supplying 4 of its 6 muscles:
Inferior oblique
Superior rectus
Inferior rectus
medial rectus
Some parasympathetic cell bodies are in ciliary ganglia

28. Cranial Nerve III: Oculomotor
Figure III from Table 13.2

29. Cranial Nerve IV: Trochlear
Fibers emerge from the dorsal midbrain
Innervate the superior oblique muscle of the eye
Functions: :
Primarily is a motor nerve
Directs the eyeball

30. Cranial Nerve IV: Trochlear
Figure IV from Table 13.2

31. Cranial Nerve V: Trigeminal
The largest cranial nerve
Fibers extend from the pons to the face
They form three divisions:
Ophthalmic (V1)
Maxillary (V2)
Mandibular (V3)
Supplies sensory fibers to the face (V1) and (V2)
Supplies motor fibers (V3) for mastication

32. Cranial Nerve V: Trigeminal
Figure V from Table 13.2

33. Cranial Nerve VI: Abducens
Fibers leave the inferior pons
Primarily a motor nerve innervating the lateral rectus muscle
Figure VI from Table 13.2

34. Cranial Nerve VII: Facial
It is a mixed nerve with five major branches:
Temporal
Zygomatic
Buccal
Mandibular
Cervical
The nerve leaves the pons
Courses to the lateral aspect of the face

35. Cranial Nerve VII: Facial
Its motor functions include:
Facial expression
Transmittal of autonomic impulses to:
Lacrimal glands
Nasal & palatine glands
Salivary glands
Its sensory function is:
Conveying impulses from taste buds (anterior two-thirds of tongue)

36. Cranial Nerve VII: Facial
Figure VII from Table 13.2

37. Cranial Nerve VIII: Vestibulocochlear
Fibers arise from hearing & equilibrium apparatus of inner ear
They pass through the internal acoustic meatus
They enter the brain stem at the pons-medulla border
The nerve has two divisions:
Cochlear (hearing)
Vestibular (balance)
Functions are solely sensory:
Equilibrium
Hearing

38. Cranial Nerve VIII: Vestibulocochlear
Figure VIII from Table 13.2

39. Cranial Nerve IX: Glossopharyngeal
Fibers emerge from the medulla
They leave the skull to the throat via the jugular foramen
It is a mixed nerve (motor & sensory functions)
It innervates part of the tongue and pharynx
Motor:
Provides somatic motor fibers to the pharynx
Provides parasympathetic motor fibers to the parotid salivary gland
Sensory:
Conducts taste & general impulses (touch, pressure, pain) from:
Pharynx & posterior tongue
Chemoreceptors in carotid body (blood CO2 & O2 monitoring)
Baroreceptors of carotid sinus (blood pressure monitoring)

40. Cranial Nerve IX: Glossopharyngeal
Figure IX from Table 13.2

41. Cranial Nerve X: Vagus
The only cranial nerve that extends beyond head & neck
Its fibers emerge from the medulla
It leaves the skull via the jugular foramen
It descends through the neck into thorax & abdomen
It is a mixed nerve (motor & sensory functions)
Most of its motor fibers are parasympathetic fibers
They supply the:
Heart
Lungs
Visceral organs

42. Its sensory function involves impulse transmission from:
Cranial Nerve X: Vagus
Its sensory function involves impulse transmission from:
Thoracic & abdominal viscera
Aortic arch baroreceptors (blood pressure)
Carotid & aortic bodies (respiration chemoreceptors)
Taste buds of posterior tongue & pharynx
Muscles of larynx & pharynx (proprioceptor fibers)

43. Cranial Nerve X: Vagus
Figure X from Table 13.2

44. Cranial Nerve XI: Accessory
Unique because it is formed from rootlets emerging from the spinal cord (not from the brain stem)
Rootlets arise from superior region of spinal cord
They pass up & enter the skull via the foramen magnum as accessory nerves
The accessory nerves leave the cranium together with the vagus nerves via the jugular foramen
They supply two large neck muscles (trapezius & sternocleidomastoid)

45. Cranial Nerve XI: Accessory
A mixed nerve, but primarily a motor nerve
Supplies motor fibers to:
Trapezius
Sternocleidomastoid
Conveys proprioceptor impulses from:
The same muscles

46. Cranial Nerve XI: Accessory (refer to new text slide)
Figure XI from Table 13.2

47. Cranial Nerve XII: Hypoglossal
Fibers arise from the medulla
They exit the skull via the hypoglossal canal
A mixed nerve, but primarily motor
Innervates:
Extrinsic & intrinsic muscles of the tongue
These muscles contribute to:
Food mixing
Swallowing
Speech

48. Cranial Nerve XII: Hypoglossal
Figure XII from Table 13.2