1. The Peripheral Nervous System (PNS) Part 1

2. Peripheral Nervous System (PNS)
Neural structures outside CNS, although soma may be w/in CNS
sensory receptors, peripheral nerves, ganglia, & motor endings
Divisions of PNS
Afferent division (sensory)
Efferent division (motor)
Somatic – innervate skeletal muscle
Autonomic – innervate smooth, cardiac, glands, visceral organs
Sympathetic – soma in spinal cord
Parasympathetic – soma in midbrain or sacrum

3. Motor neurons of somatic division
Efferent Division
Motor neurons of somatic division
Terminate at motor end plate
neuromuscular junction
Motor neurons of autonomic division
Varicosities in smooth & cardiac muscle & glands

4. Afferent Division - Sensory Neurons
Sensory neuron termini (dendritic processes) specialized to respond to stimuli
Activation triggers impulses to CNS
Perception in brain

5. Receptor Classification by Stimulus Type
Mechanoreceptors – change in neuron shape
Thermoreceptors - temperature
Photoreceptors - light
Chemoreceptors - chemicals
Nociceptors – pain-causing stimuli (chemicals)

6. Receptor Classification by Location:
Exteroceptors
Near body surface
Respond to stimuli arising outside body
Include special sense organs
Interoceptors
Respond to stimuli arising w/in body
Found in internal viscera & blood vessels
Proprioceptors
Respond to stretch
In skeletal muscles, tendons, joints, ligaments, & connective tissue

7. Receptor Classification by Structure
Simple
Dendritic process triggered directly by stimulus
Encapsulated or unencapsulated
nociceptors
touch/pressure
Complex
Receptor cells w/in special sense organs
Sensory neuron stimulated by bipolar neuron
Photoreceptors
Mechanoreceptors
Olfactory receptors
Gustatory receptors

8. Table

9. Table

10. Adaptation of Sensory Receptors
sensory receptors subjected to unchanging stimulus
Receptor membranes become less responsive
Receptor potentials decline in frequency or stop
Pressure, touch, & smell receptors adapt quickly
Merkel’s discs, Ruffini’s corpuscles, & interoceptors for blood chemicals adapt slowly
Pain receptors & proprioceptors do not adapt

11. Structure of a Nerve

12. Classification of Nerves by Directionality
Sensory (afferent) – signals TO CNS
Motor (efferent) – signals FROM CNS
Mixed –
both sensory & motor
most common
somatic & autonomic signals

13. Regeneration of Nerve Fibers
Mature neurons are amitotic
If soma remains intact, neuron can regenerate
Figure 13.4

14. 12 pairs of nerves directly from brain Sensory, motor, or mixed
Cranial Nerves
12 pairs of nerves directly from brain
Sensory, motor, or mixed
I - XII according to anterior level of origin
Named by to innervated organs/function
Four cranial nerves carry parasympathetic fibers serving muscles & glands

15. Cranial Nerves

16. Summary of Cranial Nerves

17. Spinal Nerves
Figure 13.6

18. Spinal Nerve Roots
(ANS)
Figure 13.7a

19. Interlacing nerve networks
Nerve Plexuses
Interlacing nerve networks
cervical
brachial
lumbar
sacral
Branches of plexus contain fibers from several nerves
Every muscle innervated by multiple spinal nerves

20. Cervical Plexus
Figure 13.8

21. Brachial Plexus
Figure 13.9a

22. Brachial Plexus: Distribution of Nerves
Figure 13.9c

23. Spinal Nerve Innervation: Back, Anterolateral Thorax, & Abdominal Wall
Figure 13.7b

24. Lumbar Plexus
Figure 13.10

25. Sacral Plexus
Figure 13.11

26. Rapid, predictable motor response to a stimulus Reflexes:
Intrinsic or acquired
Involve only PNS & spinal cord
Can relay to higher brain centers
Somatic reflexes – skeletal muscle
Autonomic reflexes – smooth muscle, glands

27. Receptor Sensory neuron Integration center Motor neuron Effector
Reflex Arc Components
Receptor
Sensory neuron
Integration center
Motor neuron
Effector
Receptor 1 2 3 4
Sensory neuron
Integration center 5
Effector
Motor neuron
Stimulus
Skin
Spinal cord (in cross-section)
Interneuron

28. Stretch & Deep Tendon Reflexes
Proprioceptors in tendons & muscle continually maintain postural contractions & muscle tone
These effects are via spinal reflex arcs

29. Muscle Spindles – Stretch Receptors
Intrafusal muscle fibers lacking myofilaments in central regions
Wrapped by type Ia & type II fibers afferent fibers
Innervated by  efferent fibers

30. Operation of Muscle Spindles
Stimulates action potential in postsynaptic neuron
Does not stimulates action potential in postsynaptic neuron

31. Stretch Reflex
Figure 13.17

32. Flexor & Crossed Extensor Reflex
Figure 13.19

33. The Autonomic Nervous System

34. Autonomic Nervous System (ANS)
Motor neurons that:
Innervate smooth & cardiac muscle & glands
Subconscious control

35. ANS differs from the SNS
Effectors
SNS – skeletal muscle
ANS – non-skeletal muscle & gland cells
Efferent pathways
SNS – single PNS neuron
ANS – 2 PNS neurons
Target organ responses
SNS – contraction of muscle
ANS – contraction or relaxation, excretion
Neurotransmitters used
SNS – acetylcholine
ANS – acetylcholine, norepinephrine & epinephrine

36. Distinctions of Efferent Pathways
SNS motor neurons
Single neuron extends from CNS to effector
Heavily myelinated axons
ANS motor neurons
Two-neuron PNS chain
Preganglionic neuron & postganglionic neuron
Lightly myelinated preganglionic axon from CNS to ganglion
Unmyelinated postganglionic axon extends to effector

37. Neurotransmitter Differences
SNS neurons release acetylcholine (ACh), which has an excitatory effect
In the ANS:
Preganglionic fibers release ACh
Postganglionic fibers
release norepinephrine or ACh
effect is stimulatory or inhibitory
effect depends on neurotransmitter receptor in cells of effector tissue

38. Comparison of Somatic & Autonomic Systems
Figure 14.2

39. Anatomy of ANS Short preganglionic Long preganglionic
Long postganglionic
Ganglia close to spinal cord
Long preganglionic
Short postganglionic
Ganglia on/in target organ
Figure 14.3

40. Parasympathetic (PANS)
Divisions of the ANS
Sympathetic (SANS)
mobilizes the body during stressful situations
Parasympathetic (PANS)
stimulates maintenance activities & conserves body energy
SANS & PANS counterbalance each other’s activity
SANS signals usually override PANS

41. Examples of ANS Effects
PANS
Lowers BP, heart & respiratory rates
Increases gastrointestinal tract activity
Superficial arterioles open (smooth muscle relaxed)
Pupils are constricted/dilated by light level only
SANS
Blood flow to organs/skin reduced, flow to muscles increased
Heart & respiratory rates increased
Iris contracts - Pupils dilate

42. Parasympathetic Division Outflow
Cranial Outflow
Cranial Nerve
Ganglion
Effector Organ(s)
Occulomotor (III)
Ciliary
Eye
Facial (VII)
Pterygopalatin Submandibular
Salivary, nasal, & lacrimal glands
Glossopharyngeal (IX)
Otic
Parotid salivary glands
Vagus (X)
Located within the walls of target organs
Heart, lungs, & most visceral organs
Sacral Outflow
S2-S4
Located within the walls of the target organs
Large intestine, urinary bladder, ureters, & reproductive organs

43. Parasympathetic Division Outflow
Longer preganglionic axons
Ganglion near/on target organ
Short postganglionic axons
Vagus nerve (CN X) innervates all visceral organs

44. Postganglionic fibers innervate the numerous organs of the body
Sympathetic Outflow
Sympathetic neurons in lateral horns of spinal cord segments T1 through L2
T1-T4 preganglionic fibers pass through the white rami communicantes & synapse in sympathetic chain ganglia
T5-L2 preganglionic fibers pass through the gray rami communicantes & chain ganglia to form splanchnic nerves & synapse in collateral ganglia around abdominal aorta
Postganglionic fibers innervate the numerous organs of the body

45. Sympathetic Outflow
Sympathetic neurons in lateral horns of spinal cord segments T1- L2
T1-T4 preganglionic fibers synapse in sympathetic chain ganglia
T5-L2 preganglionic fibers form splanchnic nerves & synapse in collateral ganglia on abdominal aorta

46. Sympathetic Trunks & Pathways

47. T1-T4 preganglionic axons synapse in the superior cervical ganglion
Pathways to the Head
T1-T4 preganglionic axons synapse in the superior cervical ganglion
Serve skin & blood vessels of the head
Stimulate dilator muscles of the iris
Inhibit nasal & salivary gland secretions

48. Pathways to the Thorax
T1-T6 preganglionic axons synapse in cervical chain ganglia
Postganglionic axons from middle & inferior cervical ganglia enter spinal nerves C4-C8 to innervate the heart, thyroid & skin of neck
Other T1-T6 preganglionic axons synapse in nearest chain ganglia to directly serve the heart, aorta, lungs, & esophagus

49. Pathways with Synapses in Collateral Ganglia
T5-L2 preganglionic axons exit sympathetic chain ganglia & form splanchnic nerves
Splanchnic nerves form aortic plexus & numerous ganglia
Postganglionic axons from abdominal ganglia innervate viscera

50. Pathways with Synapses in the Adrenal Medulla
Axons of the thoracic splanchnic nerve go directly to the adrenal medulla
Upon stimulation, medullary cells secrete norepinephrine & epinephrine into the blood
greater thoracic splanchnic nerve

51. Visceral Reflexes
Visceral reflexes have the same elements as somatic reflexes
Afferent fibers are found in spinal & autonomic nerves

52. ANS Neurotransmitters
PANS
Acetylcholine (ACh) released by pre- & postganglionic axons
SANS
ACh released by preganglionic axons
ACh or norepinephrine (NE) released by postganglionic axons
Cholinergic fibers – ACh-releasing axons
Adrenergic fibers –NE-releasing postganglionic SANS axons
Excitatory or inhibitory effects depend upon the receptor type

53. Cholinergic Receptors
Bind ACh
Nicotinic receptors
Muscarinic receptors
Named & distinguished by interaction w/ agonists
Nicotine
Muscarine
Agonist – stimulates effect
Antagonist – blocks effect

54. Cholinergic Receptors
Nicotinic Receptors
Locations:
Skeletal muscle motor end plates, CNS neurons
SANS & PANS ganglionic neurons
Adrenal medulla cells
Ion channels
ACh always stimulatory
Muscarinic Receptors
Locations
Cells stimulated by postganglionic PANS fibers, CNS
ACh inhibition or excitation depends on receptor subtype
subtypes – M1, M2, M3

55. Receptors that bind to norepinephrin & epinephrine
Adrenergic Receptors
Receptors that bind to norepinephrin & epinephrine
In cells innervated by SANS postganglionic axons
Alpha
subclasses - 1, 2,
NE is stimulatory
Beta
Subclasses - 1, 2 , 3
NE is generally inhibitory
Exception – NE binding to  receptors of the heart is stimulatory

56. Drugs that Influence the ANS
Table

57. Levels of ANS Control
Figure 14.9

58. Interactions of the Autonomic Divisions
Most visceral organs innervated by both sympathetic & parasympathetic fibers
results in dynamic antagonisms that precisely control visceral activity
Sympathetic fibers increase heart & respiratory rates, & inhibit digestion & elimination
Parasympathetic fibers decrease heart & respiratory rates, & allow for digestion & the discarding of wastes