1. Chapter 18 *Lecture Outline
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2. Chapter 18 Outline
Comparison of the Somatic and Autonomic Nervous Systems
Overview of the Autonomic Nervous System
Parasympathetic Division
Sympathetic Division
Other Features of the Autonomic Nervous System
CNS Control of Autonomic Function
Development of the Autonomic Nervous System

3. Autonomic Nervous System
The autonomic nervous system (ANS) is a complex system of nerves that govern involuntary actions.
The ANS works constantly with the somatic nervous system (SNS) to regulate body organs and maintain normal internal functions.

4. Autonomic Nervous System
The ANS and SNS are part of both the central nervous system and the peripheral nervous system.
The SNS operates under our conscious control. The ANS functions are involuntary and we are usually unaware of them.

5. Comparison of Somatic and Autonomic Nervous Systems
Figure 18.1

6. Comparison of Somatic and Autonomic Nervous Systems
Both the SNS and the ANS use sensory and motor neurons.
In the SNS, somatic motor neurons innervate skeletal muscle fibers, causing conscious voluntary movement.
ANS motor neurons innervate smooth muscle fibers, cardiac muscle fibers, or glands.
ANS motor neurons can either excite or inhibit cells in the viscera.

7. Comparison of Somatic and Autonomic Nervous Systems
SNS—single lower motor neuron axon extends uninterrupted from the spinal cord to one or more muscle fibers
ANS—two-neuron chain innervates muscles and glands

8. Components of the Autonomic Nervous System
Figure 18.2

9. Comparison of Somatic and Autonomic Motor Nervous Systems

10. Two-Neuron Chain in ANS
The first neuron in the ANS pathway is the preganglionic neuron. Its cell body is in the brain or spinal cord.
A preganglionic axon extends to the second cell body housed within an autonomic ganglion in the peripheral nervous system.
The second neuron in the pathway is called a ganglionic neuron.
A postganglionic axon extends from its cell body to effector (target) cells.

11. Two-Neuron Chain in ANS
Neuronal convergence—axons from numerous preganglionic cells synapse on a single ganglionic cell
Neuronal divergence—axons from one preganglionic cell synapse on numerous ganglionic cells

12. Divisions of Autonomic Nervous System
Parasympathetic division—conservation of energy and replenishment of nutrient stores (“rest-and-digest”)
Sympathetic division—preparation of body for emergencies (“fight-or-flight”); increased activity of this division results in increased alertness and metabolic activity

13. Comparison of Parasympathetic and Sympathetic Divisions
Figure 18.3

14. Anatomic Differences Between Parasympathetic and Sympathetic Neurons
Figure 18.4

15. Comparison of Sympathetic and Parasympathetic Divisions

16. Parasympathetic Division
Termed craniosacral division because preganglionic neurons are housed within nuclei in the brainstem and within lateral gray regions of the S2–S4 spinal cord segments
Ganglionic neurons are found in either terminal ganglia close to the target organ, or intramural ganglia in the wall of the target organ

17. Overview of Parasympathetic Pathways
Figure 18.5

18. Four Cranial Nerves of Parasympathetic Division
1. Oculomotor (CN III)
2. Facial (CN VII)
3. Glossopharyngeal (CN IX)
4. Vagus (CN X)

19. Oculomotor Nerve (CN III)
Preganglionic cell bodies housed in nuclei in mesencephalon
Postganglionic cell bodies located in ciliary ganglion within the orbit
Postganglionic axons project to the ciliary muscle and to the pupillary constrictor muscle of iris

20. Facial Nerve (VII)
Two branches of preganglionic axons in the facial nerve (VII) exit the pons:
1. greater petrosal nerve
2. chorda tympani

21. Facial Nerve (VII) Greater petrosal nerve:
terminates at the pterygopalatine ganglion
postganglionic axons project to lacrimal glands and small glands of nasal cavity, oral cavity, and palate

22. Facial Nerve (VII) Chorda tympani:
terminates at the submandibular ganglion
postganglionic axons project to submandibular and sublingual salivary glands in the floor of the mouth

23. Glossopharyngeal Nerve (CN IX)
Preganglionic axons exit brainstem
Preganglionic axons branch and synapse on ganglionic neurons in the otic ganglion
Postganglionic axons cause increase in secretion from parotid salivary glands

24. Vagus Nerve (CN X)
Projects inferiorly through neck to supply innervation to thoracic organs and most abdominal organs
Multiple branches extend to thoracic organs to increase mucous production and decrease diameter of airways, and to decrease heart rate and force of heart contraction

25. Vagus Nerve (CN X)
Vagal trunks pass through diaphragm, associate with the abdominal aorta, and project branches to ganglia located adjacent to or within wall of target organs
Increases smooth muscle motility and secretory activity in digestive tract organs

26. Spinal Sacral Nerves
Preganglionic neuron cell bodies are housed within lateral gray regions of S2–S4 spinal cord segments.
Preganglionic axons branch to form pelvic splanchnic nerves, which contribute to the superior and inferior hypogastric plexus.
Preganglionic fibers project to ganglionic neurons within terminal or intramural ganglia of large intestine, rectum, reproductive organs, urinary bladder, and distal ureter.

27. Parasympathetic Division Outflow

28. Sympathetic Division
Also termed thoracolumbar division because preganglionic neuron cell bodies are housed in lateral horn between first thoracic (T1) and second lumbar (L2) spinal segments
Preganglionic axons travel with somatic motor neuron axons to exit the spinal cord and enter the anterior roots and then the T1–L2 spinal nerves

29. Right and Left Sympathetic Trunks
Sympathetic trunks are located anterior to spinal nerves and immediately lateral to vertebral column.
Sympathetic trunk ganglia (paravertebral or chain ganglia) house sympathetic ganglionic neuron cell bodies. One sympathetic ganglion is approximately associated with each spinal nerve.
Cervical portion of each sympathetic trunk is partitioned into three ganglia: the superior, middle, and inferior ganglia.

30. Overview of Sympathetic Pathways
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Preganglionic
Eye
Postganglionic
Blood vessels and
sweat glands of head
Salivary glands
Blood vessels
Heart
Cardiac and
pulmonary
plexuses
Right
Left
Superior cervical ganglion
Middle cervical ganglion
Inferior cervical ganglion
Greater thoracic splanchnic nerve T1 T1 T1
Celiac ganglion
Lung
Lesser thoracic splanchnic nerve T2 T2
gallbladder
Liver and T3 T3
Stomach T4 T4
Spleen
Adrenal medulla T5 T5
Superior
mesenteric
ganglion
Kidney T6 T6
Ureter (proximal) T7 T7
Pancreas
Large intestine T8 T8
Small intestine T9 T9
T10
T10
T11
T11
Inferior
mesenteric
ganglion
Postganglionic fibers
to skin, blood vessels
T12
T12
Rectum L1 L1
Ureter (distal) L2 L2 L2
Least thoracic splanchnic nerve
Lumbar splanchnic nerves L3
Hypogastric plexus
Bladder
Spinal cord L4
Sacral splanchnic nerves L5
Vas deferens S1
Seminal vesicle
Sympathetic chain ganglia S2
Prostate
Ovary
Uterus
Testis
Figure 18.6

31. Sympathetic Trunk
Figure 18.7

32. Cervical Sympathetic Ganglia
Postganglionic axons from cell bodies in the superior cervical ganglion distribute to structures in the head and neck. Axons innervate sweat glands, smooth muscle in blood vessels, dilator pupillae muscle of the eye, and the superior tarsal muscle of the eye.
Middle and inferior cervical ganglia house neuron cell bodies that extend postganglionic axons to the thoracic viscera.

33. Rami Communicantes Connect sympathetic trunk to each spinal nerve
Preganglionic sympathetic axons of T1–L2 spinal nerves are carried by white rami communicantes (or white rami)

34. Rami Communicantes
Postganglionic sympathetic axons are carried from the sympathetic trunk to the spinal nerve by gray rami communicantes (or gray rami). Gray rami connect to all spinal nerves including cervical, sacral, and coccygeal spinal nerves.
Preganglionic axons of white rami are myelinated and postganglionic axons of gray rami are unmyelinated.

35. Splanchnic Nerves
Composed of preganglionic sympathetic axons that did not synapse in a sympathetic trunk ganglion
Run anteriorly from sympathetic trunk to most of viscera

36. Splanchnic Nerves
Larger nerves are preganglionic axons that extend from sympathetic trunk ganglia:
Greater thoracic splanchnic nerves: T5–T9
Lesser thoracic splanchnic nerves: T10–T11
Least thoracic splanchnic nerves: T12
Lumbar splanchnic nerves: L1 and L2
Sacral splanchnic nerves: sacral sympathetic ganglia

37. Prevertebral (Collateral) Ganglia
Splanchnic nerves typically terminate in prevertebral ganglia.
Ganglia are unpaired and immediately anterior to the vertebral column on the anterolateral surface of the aorta in the abdominopelvic cavity.

38. Prevertebral (Collateral) Ganglia
Ganglia typically cluster around the major abdominal arteries and are named for the arteries.
Sympathetic postganglionic axons extend away from the ganglionic neuron cell bodies in the ganglia and innervate many of the abdominal organs.

39. Prevertebral Ganglia Prevertebral ganglia include: Celiac ganglion
Superior mesenteric ganglion
Inferior mesenteric ganglion

40. Celiac Ganglion Location—adjacent to origin of celiac artery
Preganglion axons—greater thoracic splanchnic nerves (T5–T9 segment of spinal cord)
Postganglionic axons—innervate stomach, spleen, liver, gallbladder, proximal duodenum, part of pancreas

41. Superior Mesenteric Ganglion
Location—adjacent to origin of superior mesenteric artery
Preganglionic axons—lesser and least thoracic splanchnic nerves (T10–T12 segment of spinal cord)
Postganglionic axons—innervate distal duodenum, part of pancreas, remainder of small intestine, proximal large intestine, kidneys, proximal part of ureters

42. Inferior Mesenteric Ganglion
Location—adjacent to the origin of the inferior mesenteric artery
Preganglionic axons—lumbar splanchnic nerves (L1–L2 segment of spinal cord)
Postganglionic axons—innervate the distal colon, rectum, urinary bladder, distal ureter, and most of reproductive organs

43. Sympathetic Pathways
All preganglionic neurons originate in lateral gray horns of T1–L2 regions of the spinal cord.
Preganglionic axons travel with T1–L2 spinal nerves.
Preganglionic axons immediately leave spinal nerve and travel through white rami to enter sympathetic trunk.

44. Sympathetic Pathways
Once inside the sympathetic trunk preganglionic axons may remain at the level of entry or travel superiorly or inferiorly within the sympathetic trunk.
Axons exit sympathetic trunk ganglia by:
spinal nerve pathway
postganglionic sympathetic nerve pathway
splanchnic nerve pathway
adrenal medulla pathway

45. Spinal Nerve Pathway
Figure 18.8

46. Postganglionic Sympathetic Nerve Pathway
Figure 18.8

47. Splanchnic Nerve Pathway
Figure 18.8

48. Adrenal Medulla Pathway
Figure 18.8

49. Adrenal Medulla Pathway
Adrenal medulla—the internal region of adrenal gland that releases hormones within the bloodstream to help promote fight-or-flight response
The hormones are epinephrine and, to a lesser degree, norepinephrine

50. Sympathetic Outflow

51. Autonomic Plexuses
Collections of sympathetic postganglionic axons, parasympathetic preganglionic axons, and visceral sensory axons
Sympathetic and parasympathetic axons are close to one another

52. Autonomic Plexuses Cardiac plexus Pulmonary plexus Esophageal plexus
Abdominal aortic plexus consists of celiac plexus, superior mesenteric plexus, inferior mesenteric plexus,
Hypogastric plexus

53. Autonomic Plexuses
Figure 18.9

54. Cardiac Plexus In mediastinum of thoracic cavity
Consists of postganglionic sympathetic axons from thoracic sympathetic trunk ganglia and preganglionic axons of vagus nerve
Increased sympathetic activity increases heart rate and blood pressure
Increased parasympathetic activity decreases heart rate

55. Pulmonary Plexus
Consists of postganglionic sympathetic axons from thoracic sympathetic trunk ganglia and preganglionic axons from the vagus nerve
Axons project to bronchi and blood vessels of the lungs
Parasympathetic stimulation reduces bronchial diameter (bronchoconstriction) and increases mucous gland secretion in bronchial tree
Sympathetic innervation causes bronchodilation (increase bronchial diameter)

56. Esophageal Plexus Consists of preganglionic axons from the vagus nerve
Parasympathetic activity coordinates smooth muscle activity during swallowing reflex in inferior wall and cardiac sphincter in inferior esophagus

57. Abdominal Aortic Plexus
Consists of celiac plexus, superior mesenteric plexus, and inferior mesenteric plexus
Composed of postganglionic axons projecting from the prevertebral ganglia and preganglionic axons from the vagus nerve

58. Hypogastric Plexus
Complex meshwork of postganglionic sympathetic axons (from the aortic plexus and the lumbar region of the sympathetic trunk) and preganglionic parasympathetic axons from the pelvic splanchnic nerve
Axons innervate viscera within the pelvic region

59. Neurotransmitters and Receptors
All preganglionic axons release acetylcholine (ACh), which has an excitatory effect on the ganglionic cell.
All postganglionic parasympathetic axons and a few postganglionic sympathetic axons release ACh on the effector.
Depending on the receptor, ACh from parasympathetic axons may have either an inhibitory or excitatory effect on the effector.

60. Neurotransmitters and Receptors
Ach released from sympathetic axons is excitatory only.
Most postganglionic sympathetic axons release norepinephrine on the effector.
Depending on the receptor, the effects of norepinephrine has an inhibitory or an excitatory effect.

61. Comparison of Neurotransmitters in the Autonomic Nervous System
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Parasympathetic Pathway
Sympathetic Pathways
Preganglionic axon releases ACh
ACh
ACh
ACh
Ganglionic neuron cell body and
dendrites always contain receptors
for ACh
ACh
receptors
ACh
receptors
ACh
receptors
Postganglionic axon releases
ACh or NE
ACh
ACh NE
ACh
receptors
ACh
receptors NE
receptors
Target cells contain either ACh
receptors (bind ACh) or NE
receptors (bind NE)
Target cell
Target cell
Target cell
Figure 18.10

62. Dual Innervation
Many visceral effectors have dual innervation, meaning innervation by postganglionic axons from both ANS divisions.
The actions of the divisions usually oppose each other (antagonistic effects).

63. Autonomic Reflexes Figure 18.11 2 3 1 4 5
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Ureters
Urinary
bladder
stretches
as it fills
with urine 2
Nerve impulse travels through sensory
neuron to integration center in the spinal cord 3
Nerve impulse is processed
in the integration center
Interneuron 1
Stimulus
activates
receptor
Spinal cord
Pelvic splanchnic nerve 4
Motor impulses are
conducted through
motor neurons
Postganglionic
axon
Ureter
Urinary bladder
Detrusor muscle contracts 5
Effector responds to
impulse from motor neuron
(smooth muscle contraction
occurs in the bladder wall
and relaxation in the internal
urethral sphincter)
Internal urethral sphincter
relaxes
Figure 18.11

64. CNS Control of Autonomic Function
Autonomic function is influenced by the:
cerebrum
hypothalamus
brainstem
spinal cord

65. Control of Autonomic Functions by Higher Brain Centers
Figure 18.12

66. CNS Control of Autonomic Function
Cerebrum:
ANS activities are affected by conscious activities in cerebral cortex and subconscious communication between association areas in the cortex with centers of sympathetic and parasympathetic control in the hypothalamus.
Sensory processing in the thalamus and emotional states controlled in the limbic system directly affect the hypothalamus.

67. CNS Control of Autonomic Function
Hypothalamus:
Integration and command center for autonomic functions
Contains nuclei that control visceral functions in both divisions of the ANS
Communicates with other CNS regions, including cerebral cortex, thalamus, brainstem, cerebellum, and spinal cord
Central brain structure involved in emotions and drives that act through the ANS

68. CNS Control of Autonomic Function
Brainstem:
Nuclei in the mesencephalon, pons, medulla oblongata mediate visceral reflexes.
Reflex centers control accommodation of the lens, blood pressure changes, blood vessel diameter changes, digestive activities, heart rate changes, and pupil size.
Centers for cardiac, digestive, and vasomotor functions are housed within the brainstem.

69. CNS Control of Autonomic Function
Spinal Cord:
Processes some autonomic responses, notably the parasympathetic activities associated with defecation and urination, without involvement of the brain
Higher centers in the brain may consciously inhibit these reflex activities

70. Neural Crest Cell Derivatives
Figure 18.13