Page 571 - Fundamentals of anatomy physiology
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558 Unit 3 Control and Regulation him, Tim appears pale and confused.
Then he becomes light-headed. His
Clinical Case vision blurs and he hears ringing in his
ears. The last thing Tim remembers is a
The First Day in Anatomy Lab sensation of profound weakness.
It is Tim’s first day in anatomy lab and he is very Tim hits the floor with a thud,
excited. He has been dreaming of this day for landing in a crumpled, prone position.
years. He has a new, white lab coat and a great anatomy and His instructor rolls him over, loosens
physiology textbook, and he is ready to go. his tie and belt, and props his lower
The first thing Tim notices upon entering the lab is the legs up on a chair. Within ten seconds
body lying on the table. A human cadaver certainly resembles a Tim regains consciousness but feels exhausted. It is as if he is
human being, but there is no mistaking the two. There are bright climbing out of a very deep sleep. He is very embarrassed.
lights and a smothering smell of formaldehyde from the em- What happened to Tim? To find out, turn to the Clinical
balming fluid used in the cadaver. Case Wrap-Up on p. 588.
Tim suddenly feels hot and sweaty. He has a vague discom-
fort in his chest and feels sick to his stomach. His instructor says
something to him but he cannot understand the words. He tries
to respond, but is unable to speak. When his instructor looks at
16 An Introduction to the Autonomic (ANS) makes routine homeostatic adjustments in physiologi-
Nervous System and Higher-Order cal systems. The ANS coordinates cardiovascular, respiratory, di-
Functions gestive, urinary, and reproductive functions. It adjusts internal
water, electrolyte, nutrient, and dissolved gas concentrations
In this chapter we focus on the autonomic nervous system in body fluids—without instructions or interference from the
(ANS), which adjusts our basic life support systems without conscious mind.
our conscious control. We also consider aspects of higher-order
functions such as consciousness, learning, and intelligence. Fi- The practice of medicine has benefitted greatly from
nally, we look at the effects of aging on the nervous system and our understanding of the ANS. For example, in 1960, the
conclude with an overview of interactions between the nervous five-year survival rate for patients after their first heart at-
system and other body systems. tack was very low. The problem was that it was difficult and
sometimes impossible to control high blood pressure. Today,
16-1 The autonomic nervous many heart attack survivors lead normal lives. What changed?
We learned to manipulate the ANS with medicine and clini-
system is involved in the unconscious cal procedures. Let’s begin our examination of the ANS by
regulation of visceral functions and comparing its organization with that of the somatic nervous
has sympathetic and parasympathetic system (SNS).
divisions
Organization of the ANS
Learning Outcome Compare the organization of the autonomic
nervous system with that of the somatic nervous system. Figure 16–1 compares the organization of the somatic and au-
tonomic nervous systems. Both are efferent divisions that carry
Your conscious thoughts, plans, and actions are a tiny fraction motor commands. The SNS controls skeletal muscles, and the
of what the nervous system does. If all consciousness were ANS controls visceral effectors such as smooth muscle, glands,
eliminated, your vital physiological processes would continue cardiac muscle, and adipocytes. The primary structural differ-
virtually unchanged. After all, a night’s sleep is not a life-threat- ence between the two is that in the SNS, motor neurons of the
ening event. Longer, deeper states of unconsciousness are not central nervous system exert direct control over skeletal muscles
necessarily more dangerous, as long as you get nourishment (Figure 16–1a). In the ANS, by contrast, motor neurons of the
and other basic care. People with severe brain injuries can sur- central nervous system synapse on visceral motor neurons in
vive in a coma for decades. autonomic ganglia, and these ganglionic neurons control vis-
ceral effectors (Figure 16–1b).
How do people survive under these conditions? Their
survival is possible because the autonomic nervous system The hypothalamus contains the integrative centers for au-
tonomic activity. The neurons in these centers are comparable
558 to the upper motor neurons in the SNS. Visceral motor neurons
