1. Chapter 15
Lecture Notes
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2. Nervous System: Autonomic Nervous System
Autonomic system
System of nerves mediating involuntary actions
Regulates body organ activity
Maintains normal internal functions
Divided into sympathetic and parasympathetic divisions
Allows for varied nervous system responses in times of stress and rest

3. Comparison of the Somatic and Autonomic Nervous Systems
Learning Objectives:
1) List the similarities and differences between the SNS and the ANS.
Compare and contrast motor neurons in the SNS and ANS.
Describe how the two-neuron chain in the ANS facilitates communication and control.

4. Comparison of the Somatic and Autonomic Nervous Systems: Functional Organization
Somatic nervous system (SNS)
Includes processes perceived or controlled consciously
Somatic sensory portion
detects stimuli from special senses, skin, and proprioceptors
sends information to CNS
Somatic motor portion
transmits nerve signals from CNS to control skeletal muscles

5. Figure 15.1a Somatic Nervous System Posterior root ganglion
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Somatic Nervous System
Figure 15.1a
Posterior root ganglion
Anterior root
Somatic sensory
neuron detects stimuli
and transmits nerve
signals from skin,
skeletal muscle, joints,
and special senses
(vision, hearing, etc.).
Somatic motor neuron
sends nerve signals to
skeletal muscle.
Skeletal muscle
Sensory receptor
in skin
(a)

6. Comparison of the Somatic and Autonomic Nervous Systems: Functional Organization
Autonomic nervous system (ANS)
Includes processes regulated below conscious level
Visceral sensory portion
detects stimuli from blood vessels and internal organs
Autonomic motor portion (visceral motor)
transmits nerve signals to cardiac muscle, smooth muscle, and glands
Functions to maintain homeostasis
constant internal environment
Regulates:
heart rate and blood pressure
respiratory rate, sweating, and digestion
Keeps these variables within optimal ranges

7. Figure 15.1b Autonomic Nervous System Autonomic ganglion
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Autonomic Nervous System
Figure 15.1b
Autonomic
ganglion
Preganglionic autonomic motor neuron
transmits nerve signals to a ganglionic
motor neuron.
Ganglionic autonomic
motor neuron transmits
nerve signals to smooth
muscle, cardiac muscle,
and glands.
Visceral sensory
neuron detects
stimuli within blood
vessels and smooth
muscle in the
viscera.
Smooth muscle
in trachea
Sensory receptor
in viscera
(b)

8. Comparison of the Somatic and Autonomic Nervous Systems: Motor Neurons
Lower motor neurons of SNS
Single lower motor neuron
extends from CNS to skeletal muscle fibers
cell body within brainstem or spinal cord
exits CNS in cranial nerve or spinal nerve
myelinated axons with large diameter
fastest conduction
always release acetylcholine (ACh) from synaptic knob

9. Comparison of the Somatic and Autonomic Nervous Systems: Motor Neurons
Lower motor neurons of ANS
Chain of two motor neurons
preganglionic neuron
cell body within brainstem or spinal cord
exits CNS in cranial nerve or spinal nerve
projects to autonomic ganglion in peripheral nervous system
releases ACh from synaptic knob
(post)ganglionic neuron
cell body within autonomic ganglion
exits ganglion to effector (cardiac muscle, smooth muscle, gland)
releases ACh or norepinephrine (NE) from synaptic knob

10. Comparison of the Somatic and Autonomic Nervous Systems: Functional Organization
What criterion is used to organize the nervous system into the SNS and the ANS?
The somatic nervous system involves processes that are perceived or controlled consciously.
The autonomic nervous system includes processes regulated below the conscious level.

11. Comparison of the Somatic and Autonomic Nervous Systems: Motor Neurons
What are the anatomic features that distinguish the motor neurons in the SNS and the ANS?
The somatic nervous system has a single lower motor neuron extending from the CNS. It has large, myelinated axons and always releases ACh.
The autonomic nervous system has a chain of two lower motor neurons extending from the CNS. The pre-ganglionic neuron synapses in a ganglion and always releases ACh. The postganglionic neuron releases ACh or NE.

12. Divisions of the Autonomic Nervous Systems
Learning Objectives:
1) Describe the general functions of parasympathetic and sympathetic divisions of the autonomic nervous system.
Compare and contrast the anatomic differences in the motor neurons and associated ganglia of the parasympathetic and sympathetic divisions.

13. Divisions of the Autonomic Nervous Systems: Functional Differences
Motor component of ANS
Subdivided into parasympathetic and sympathetic divisions
Parasympathetic division
functions to maintain homeostasis at rest
energy conservation and replenishing stage
“rest-and-digest” division
Sympathetic division
prepares the body for emergencies
“fight-or-flight” division
increased alertness and metabolic activity
“three E’s”: emergency, exercise, or excitement

14. Divisions of the Autonomic Nervous Systems: Functional Differences
The parasympathetic division is responsible for what main functions?
Maintains homeostasis at rest, conserves energy, and replenishes nutrient stores

15. Divisions of the Autonomic Nervous Systems: Anatomic Differences
Parasympathetic
Preganglionic neuron in brainstem or S2-S4 spinal cord
Termed craniosacral division
Ganglionic neuron innervating muscles or glands
Preganglionic axons longer
Postganglionic axons shorter
Ganglia close to or within effector
Sympathetic
Preganglionic neuron in lateral horns of T1-L2
Termed thoracolumbar division
Ganglionic neuron innervating muscles or glands
Preganglionic axons shorter
Postganglionic axons longer
Ganglia relatively close to spinal cord

16. Figure 15.3 Autonomic Motor Nervous System Parasympathetic Division
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Autonomic Motor Nervous System
Parasympathetic Division
Sympathetic Division
Origin:
Preganglionic neurons located
in brainstem nuclei and S2–S4
segments of spinal cord
(craniosacral)
Origin:
Preganglionic neurons
located in lateral horns of
T1– L2 segments of spinal
cord (thoracolumbar)
CN III (oculomotor)
CN VII (facial)
Functions:
• “Rest-and-digest” response
• Brings body to homeostasis
CN IX (glossopharyngeal)
Functions:
• Activated in emergency
situations
• “Fight-or-flight” response
• Also involved with
homeostasis
Sympathetic trunk
CN X (vagus)
T1–L2 segments
of spinal cord
S2–S4 segments
of spinal cord
Pelvic splanchnic
nerves

17. (close to or within effector organ wall)
Figure 15.4
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Parasympathetic Division
Sympathetic Division
Short, branching
preganglionic axon
Ganglionic
neuron
Short
postganglionic
axon
Preganglionic
neuron
Long postganglionic axon
Long preganglionic axon
Preganglionic
neuron
Ganglionic neuron
Autonomic ganglion
(close to or within effector organ wall)
Autonomic ganglion
(close to the vertebral column)
(a)
(b)

18. Divisions of the Autonomic Nervous Systems: Anatomic Differences
Compare the parasympathetic and sympathetic divisions, in terms of types of axons and locations of ganglia.
The parasympathetic division has short axons with relatively few branches and ganglia located close to or within the wall of the organ.
The sympathetic division has long axons with many branches and ganglia located in the sympathetic trunk or prevertebral ganglia.

19. Divisions of the Autonomic Nervous Systems: Degree of Response
Parasympathetic activation
Local response
Due to long preganglionic neurons with limited branches

20. Divisions of the Autonomic Nervous Systems: Degree of Response
Sympathetic activation
Usually many structures activated simultaneously
termed mass activation
sometimes only single effector activated
Due to short preganglionic neurons with many branches
Especially important in response to stress
e.g., multiple changes during exercising
increased heart rate, blood pressure, breathing rate, pupil dilation, etc.
See Table 15.2: Comparison of Parasympathetic and
Sympathetic Divisions

21. Interactions Between the Parasympathetic and Sympathetic Divisions
Learning Objectives:
1) Discuss the nature of autonomic tone and its effects.
Explain what is meant by dual innervation.
Describe the antagonistic and cooperative effects of dual innervation.
Describe the systems innervated only by the sympathetic division and how they function.

22. Interactions Between the Parasympathetic and Sympathetic Divisions: Autonomic Tone
Most organs innervated by both divisions of ANS
Termed dual innervation
Stimulating continuously to varying degrees
referred to as autonomic tone

23. Interactions Between the Parasympathetic and Sympathetic Divisions: Autonomic Tone
E.g., diameter of most blood vessels in a partially constricted state
due to sympathetic tone
Decrease in stimulation below tone
causes vessel dilation
Increase above sympathetic tone
causes greater vessel constriction
See Table 15.5: Effects of the Parasympathetic and Sympathetic Divisions
See Figure 15.11: Comparison of the Parasympathetic and Sympathetic Divisions of the ANS

24. Interactions Between the Parasympathetic and Sympathetic Divisions: Dual Innervation
Antagonistic Effects
Parasympathetic and sympathetic effects usually antagonistic
E.g., control of heart rate
parasympathetic stimulation slowing heart rate
sympathetic stimulation increasing heart rate
same cells with both muscarinic and adrenergic receptors
E.g., control of muscular activity in GI tract
parasympathetic stimulation accelerating rate of contraction and motility
sympathetic stimulation decreasing motility
same cells with both types of receptors

25. Interactions Between the Parasympathetic and Sympathetic Divisions: Dual Innervation
Antagonistic Effects (continued)
E.g., control of pupil diameter in the eye
parasympathetic stimulation of circular muscle layer of iris
causes pupil constriction
sympathetic stimulation of radial muscle layer of iris
causes pupil dilation
different effectors innervated

26. Interactions Between the Parasympathetic and Sympathetic Divisions: Dual Innervation
Cooperative Effects
When both parasympathetic and sympathetic produce single result
E.g., male sexual function
penis erect due to parasympathetic innervation
ejaculation due to sympathetic innervation

27. Interactions Between the Parasympathetic and Sympathetic Divisions: Dual Innervation
What are the antagonistic effects of the sympathetic and parasympathetic divisions on pupil size?
Parasympathetic stimulation causes pupil constriction, due to stimulation of the circular muscle layer in the iris.
Sympathetic stimulation causes pupil dilation, due to stimulation of the radial muscle layer in the iris.

28. Parasympathetic and Sympathetic Interactions: Systems Controlled Only by Sympathetic Division
Opposing effects without dual innervation
E.g., blood vessels
cause increased smooth muscle contraction and blood pressure
vasodilation achieved by decreasing stimulation below autonomic tone
E.g., sweat glands in the trunk and arrector pili muscles in the skin
cause sweating and “goosebumps”
E.g., neurosecretory cells of adrenal medulla
release epinephrine and norepinephrine, prolonging fight-or-flight effects

29. Parasympathetic and Sympathetic Interactions: Systems Controlled Only by Sympathetic Division
What are the body structures innervated by the sympathetic division only?
Many blood vessels, sweat glands in the trunk, arrector pili in the skin, adrenal medulla

30. Control and Integration of Autonomic System Function
Learning Objectives:
1) Discuss how autonomic reflexes help maintain homeostasis.
Describe some major types of autonomic reflexes.
Describe the CNS hierarchy that controls the autonomic nervous system.

31. Control and Integration of Autonomic System Function: Autonomic Reflexes
Enable ANS to control visceral function
Consist of:
smooth muscle contractions
cardiac muscle contractions
or secretions of glands
Mediated by autonomic reflex arcs in response to stimulus

32. Control and Integration of Autonomic System Function: Autonomic Reflexes
Autonomic reflex examples
Cardiovascular reflex
stretch receptors stimulated in blood vessel walls with pressure elevation
signals propagated to cardiac center in medulla oblongata
inhibit sympathetic and activate parasympathetic output to heart
slows heart rate and decreases volume ejected
decreases blood pressure

33. Control and Integration of Autonomic System Function: Autonomic Reflexes
Autonomic reflex examples (continued)
Gastrointestinal reflex
control proximal GI tract
stimulates secretion of gastric glands by parasympathetic stimulation
stimulated by sight or smell of food
control rectum
stretch of rectum by fecal matter walls
parasympathetic reflex causing contraction to aid elimination

34. Control and Integration of Autonomic System Function: Autonomic Reflexes
Autonomic reflex examples (continued)
Micturition reflex
mechanism leading to bladder emptying
stretch receptors signaling when urine fills
results in reflex contraction of smooth muscles in bladder
results in relaxation of urinary sphincter
in toilet-trained individuals
urination follows voluntary relaxation of external urethral sphincter

35. Control and Integration of Autonomic System Function: Autonomic Reflexes
Autonomic reflex examples (continued)
Other reflexes
alter respiratory rate and depth
regulate digestive system activities
change pupil diameter

36. Figure 15.13 Ureters Urinary bladder stretches as it fills with urine.
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Ureters
Urinary
bladder
stretches
as it fills
with urine. 2
Nerve signals are transmitted along sensory
neuron to integration center in the spinal cord. 3
Sensory nerve signals are processed
in the integration center.
Sensory neuron
Interneuron 1
Stimulus
activates
receptor.
Spinal cord
Pelvic splanchnic nerve 4
Nerve signals are
transmitted along
motor neurons (via
the pelvic splanchnic
nerves) to an effector.
Postganglionic
axon
Ureter
Urinary bladder
Smooth muscle contracts. 5
Effector responds:
smooth muscle in the
bladder wall contracts
and the internal urethral
sphincter relaxes.
Internal urethral sphincter
relaxes.

37. How does the cardiovascular reflex affect blood pressure?
Control and Integration of Autonomic System Function: Autonomic Reflexes
How does the cardiovascular reflex affect blood pressure?
When blood pressure elevates, stretch receptors in large blood vessels are stimulated. They signal the cardiac center in the medulla. These nerve signals inhibit sympathetic output and activate parasympathetic output to the heart. This slows the heart rate and decreases the volume of blood ejected, decreasing blood pressure.

38. Control and Integration of Autonomic System Function: CNS Control of the ANS
Involvement of CNS
ANS is a regulated nervous system, not independent
Influenced by four CNS regions:
cerebrum, hypothalamus, brainstem, and spinal cord

39. Figure 15.14 Cerebrum Conscious activities in the
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Cerebrum
Conscious activities in the
cerebrum affect hypothalamus
control of the ANS
Hypothalamus
Integration and command center
for autonomic functions; involved in emotions
Brainstem
Contains major ANS reflex
centers
Spinal cord
Contains ANS reflex centers for
defecation and urination

40. Control and Integration of Autonomic System Function: CNS Control of the ANS
What CNS structure is the integration and command center for autonomic function?
The hypothalamus