Download Chapter 16: The Autonomic System and Higher

Chapter 16: The Autonomic System and Higher-Order Functions
Learning Outcomes
 Upon completing this chapter, you will be able to
 16-1 Compare the functions of the autonomic nervous system with that of the somatic nervous
system.
 16-6 Discuss the functional significance of dual innervation and autonomic tone. Discuss
examples of organs that are controlled by dual innervation vs. single division of ANS and the
result on autonomic tone.
 16-7 Describe or recognize an example of a visceral reflex.
 Compare and contrast the sympathetic and parasympathetic divisions of the ANS
 Describe the structure and function of the RAS and describe its importance in the sleep-wake
cycle.
Chapter 16: The Autonomic System and Higher-Order Functions
I.
Introduction to Autonomic Nervous System
A. Makes routine homeostatic adjustments (adjusts internal water, electrolyte, nutrient
and dissolved gas concentrations in body fluids)
B. Adjustments occur without instructions from conscious mind/occur at subconscious
level
II.
16-1 Somatic vs. Autonomic Nervous System
A. Somatic Nervous system (SNS)
1. Operates under conscious control
2. Seldom affects long-term survival
3. controls skeletal muscles
B. Autonomic Nervous System (ANS)
1. Operates without conscious instruction
2. controls visceral effectors (smooth muscles, glands, cardiac muscle)
3. Coordinates system functions
III.
The Organization of the Autonomic Nervous Systems
A. Efferent division that carry motor commands
B. Integrative centers for autonomic activity found in hypothalamus
C. Preganglionic neurons: visceral motor neurons in brains stem/spinal cord (CNS)
1. part of visceral reflex arcs
2. activities represent direct reflex responses
3. contain preganglionic fibers which leave CNS and synapse at visceral motor
neurons (autonomic ganglia) innervating smooth muscle, glands, cardiac muscle
D. Autonomic ganglia (PNS)
1. innervate smooth muscle, glands, cardiac muscle
2. axons called postganglionic fibers
E. visceral/sensory info triggers visceral reflexes
F. ANS distributes motor commands of those reflexes
1. Example: cold weather = ANS stimulate contraction of arrector pili muscles =
goosebumps
2. Example: loud noise = increase heart rate by ANS
IV.
Divisions of the ANS
A. Sympathetic vs. Parasympathetic Division
1. Usually have opposing effects (sympathetic = excitation and parasympathetic =
inhibition)
2. May work independently or together
Chapter 16: The Autonomic System and Higher-Order Functions
B. Functional comparison of the divisions of the ANS
Sympathetic Division (“Fight or Flight”)
Parasympathetic Division (Rest and Digest”)
Kicks in during exertion, stress or emergency situations
Kicks in under resting conditions
Increases:
Alertness/awareness
Metabolic rate
Respiration
Cardiovascular
Activates sweat glands
Increases:
Digestion
Salivary gland secretions
Elimination
Reduces:
Digestion/urinary
Decreases:
Reduces metabolic rate
Cardiovascular
C. Structural comparison of the divisions of the ANS
Sympathetic Division
Location of CNS (preganglionic)
Thoracocolumbar (Thoracic and
neurons
Lumbar Regions)
Locations of PNS ganglia
 Paravertebral (both sides
of vertebral column)
 collateral (anterior to
vertebral column)
 suprarenal (center of
adrenal gland)
Length of preganglionic fibers to
Short to long
postganglionic fibers
Neurotransmitters released by
ACh
preganglionic fibers
Parasympathetic Division
Craniosacral (Cranial and
Sacral Regions)
 Terminal (located near
target organ)
 Intramural (embedded
in tissue of target
organ)
Long to short
ACh
Neurotransmitters released by
preganglionic fibers
Most release Norepinephrine (NE)
ACh
Degree of Divergence
Great divergence (single
preganglionic fiber may innervate
24 or more ganglionic neurons in
different ganglia)
Little divergence (single
pregalnglionic fiber synapses
w/ 6-8 ganglionic neurons)
Chapter 16: The Autonomic System and Higher-Order Functions
V.
16-6 Dual Innervation
A. Most vital organs innervated by both sympathetic and parasympathetic divisions
B. Postganglionic fibers of each division “mingle” to form autonomic plexuses (Example
cardiac plexus)
C. Autonomic Tone
1. Autonomic motor neurons maintain resting level of spontaneous activity
2. Background level = autonomic tone
3. If nerve is inactive under normal conditions, can only increase activity
4. If nerve maintains background level of activity, can increase or decrease activity
D. Dual Innervation and Autonomic Tone
1. Dual innervation = two divisions commonly have opposing effects
a. Example:
i.
Heart receives dual innervation
ii.
Parasympathetic releases ACh = decrease HR
iii.
Sympathetic division release NE = increase HR
iv.
Balance between two = autonomic tone
2. No dual innervation = only one ANS innervation controls response
a. Example:
i.
Blood vessels controlled by sympathetic division
ii.
Sympathetic division release NE = increase partial contraction of
BVs = autonomic tone
iii.
Decrease in NE = dilation of BVs
VI.
16-7 Visceral Reflexes
A. Provide automatic motor responses that can be modified, facilitated or inhibited by
higher centers, such as hypothalamus
B. All are polysynaptic, can be long or short
1. Long reflexes coordinate activities of entire organs, involves CNS
2. Short reflexes bypass CNS and control activity in one small part of organ
C. Examples of Visceral Reflexes Table 16-4
VII.
16-8 Consciousness and Reticular Activating System (RAS)
A. RAS: network found in brain stem
B. Interacts with cerebral cortex via nuclei in thalamus
C. Stimulus = RAS active = cortex active = arousal from sleep + maintaining consciousness
D. Neural fatigue/decrease in response to stimuli = RAS inactive = cortex inactive =
decrease in alertness + lethargy