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Chapter 16:

The Autonomic Nervous System and
Higher-Order Functions
Introduction
The ANS adjust our basic life support systems without our conscious control
...


16-1
The autonomic nervous system is involved in the unconscious
regulation of visceral functions and has sympathetic and
parasympathetic divisions
The ANS makes routine homeostatic adjustments in physiological systems
...
It adjusts internal water,
electrolyte, nutrient, and dissolved gas concentrations in body fluids---without instructions or
interference from the conscious mind
...

The SNS controls skeletal muscles, and the ANS controls visceral effectors such as smooth muscle,
glands, cardiac muscle, and adipocytes
...

The hypothalamus contains the integrative centers for autonomic activity
...


Preganglionic neurons) what the visceral motor neurons in the brain stem and spinal cord are
known as because they extend to ganglia
...


Preganglionic fibers) what the axons of preganglionic neurons are called
...

These ganglia, which contain 100's of 1000's of ganglionic neurons are called
...


Tips & Tricks
Each autonomic ganglion functions somewhat like a baton handoff in a relay race
...


Divisions of the ANS
The subdivisions of the ANS:

(SNS) Sympathetic division----Thoracolumbar
(PNS) Parasympathetic division----Craniosacral
(SNS) Sympathetic division---Thoracolumbar

(PNS) Parasympathetic division---Craniosacral

(fight or flight)

(rest and digest)

Preganglionic neurons:
are located in the lateral gray
horns of spinal segments T1 - L2

Organs:
•

Eye

•

Preganglionic neurons:
in the brain stem and in lateral
portion of anterior gray horns of

Organs:

Skin

•

Salivary glands

Salivary glands

•

Heart

•

Lungs

•

Lungs

•

Heart

•

Stomach/sm
...
Preganglionic fibers
release AcH, stimulating
ganglionic neurons
...
Preganglionic fibers
release AcH, stimulating
ganglionic neurons
...


•

Adrenal

Pancreas
Liver and

Gallbladder

Liver and

Gallbladder

•
•

sm
...
Intestine

postganglionic fibers release AcH
at neuroeffector junctions
...
Intestine

•

Bladder

•

Genitals

2

Chapter 16:

Summarization of the general pattern of responses to increased levels of
sympathetic activities:
1
...
Increased metabolic rate
3
...
Activation of energy reserves
5
...
Increased heart rate and blood pressure
7
...
Decreased metabolic rate
2
...
Increased secretion by salivary and digestive glands
4
...
Stimulation of urination and defecation

The Enteric Nervous System
Enteric nervous system (ENS) a 3rd division of the ANS: The ENS an extensive network
of neurons and nerve networks in the walls of the
digestive tract
...

They operate without instructions from the CNS
...
It also uses the same neurotransmitters found in the
brain
...

The cell bodies of the preganglionic neurons are in the lateral gray horns, and their axons enter
the ventral roots of these segments
...


Sympathetic Chain Ganglia: also called paravertebral ganglia, lie on both sides of the
vertebral column
...


2
...
These ganglia contain ganglionic neurons that innervate tissues and organs in the
abdominopelvic cavity
...


Adrenal Medullae: what the center of each adrenal gland is known as or suprarenal
medulla
...
The ganglionic neurons of the adrenal medulla
have very short axons
...
This mode of release allows the neurotransmitters to function as
hormones, affecting target cells throughout the body
...


Postganglionic fibers
Are relatively long, except at the adrenal
medullae
...
They diverge extensively on 2 dozen or more ganglionic neurons
...

Each ganglion in the sympathetic chain innervates a particular body segment or group of
segments
...

These postganglionic fibers innervate sweat glands, smooth muscles in superficial blood
vessels, and arrector pili muscles
...


Cranial nerves III, VII, IX, and X

In Summary:
•

The cervical, inferior lumbar, and sacral chain ganglia receive preganglionic
fibers from spinal segments T1 – L2
• Only the thoracic and superior lumbar ganglia (T1 – L2) receive preganglionic
fibers from white rami
• Every spinal nerve receives a gray ramus from a ganglion of the sympathetic
chain

5

Chapter 16:

Collateral Ganglia
The abdominopelvic viscera receive sympathetic innervation by sympathetic preganglionic
fibers that synapse in separate collateral ganglia
...

They form the
...
The splanchnic nerves
innervate 3 collateral ganglia
...

Preganglionic fibers from the lumbar segments form splanchic nerves that end at the inferior
mesenteric ganglion
...


Adrenal Medullae
Preganglionic fibers synapse on neuroendocrine cells, specialized neurons that secrete
hormones into the bloodstream
...

The rest is NE or norepinephrine
...

They differ, however, in 2respects:
1
...

The effects last much longer than those produced by direct sympathetic innervation, because
the hormones continue to diffuse out of the bloodstream for an extended period
...
It is controlled by sympathetic centers in the hypothalamus
...

In general, the effects of NE on the postsynaptic membrane last for a few seconds, significantly longer
than 20msec duration of AcH effects
...

• AcH causes vasodilation
• NE causes vasoconstriction

This means that the sympathetic division can increase blood flow to the skeletal muscles, by releasing
AcH to activate cholinergic terminals
...

The sympathetic division also includes nitroxidergic synapses, which release nitric oxide (NO)
as a neurotransmitter
...
Preganglionic Neurons in the Brain Stem
and in the Sacral Segments of the Spinal
Cord:
2
...
In sacral segments of the spinal cord, the parasympathetic
nuclei lie in the lateral gray horns of spinal segments S2 –
S4
Preganglionic fibers of the parasympathetic division do not
diverge as extensively as do those of the sympathetic
division
...


Parasympathetic Activation
The functions of the parasympathetic division center on relaxation, and food processing, and
nutrient absorption
...


The major effects of the parasympathetic division include the following:

↓
•

Constriction of the pupils (to restrict the amount of light that enters the eyes) and focusing the
lenses of the eyes on nearby objects

•

Secretion by digestive glands, including salivary glands, gastric glands, duodenal glands,
intestinal glands, the pancreas (exocrine and endocrine)

•

Secretion of hormones that promote the absorption and use of nutrients by peripheral cells

•

Changes in blood flow and glandular activity associated with sexual arousal

•

An increase in smooth muscle activity along the digestive tract

•

The stimulation and coordination of defecation

•

Contraction of the urinary bladder during urination

•

Constriction of the respiratory passageways

•

A reduction in heart rate and force of contraction

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Chapter 16:

16-5
Stimulation of the Parasympathetic neurons leads to the release
of the neurotransmitter AcH
All parasympathetic neurons release AcH as a neurotransmitter
...


Membrane Receptors and Responses
The parasympathetic division uses the same transmitter, AcH, at all of its synapses (neuron to
neuron) and neuromuscular or neuroglandular junctions
...


2types of AcH receptors occur on the postsynaptic membranes:
Nicotinic receptors) occur on ganglion cells of both ANS divisions
...


2
...
Muscarinic receptors are G protein-coupled receptors
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16-6
The sympathetic and parasympathetic divisions interact,
creating dual innervation
The sympathetic division has widespread impact, reaching organs and tissues throughout the
body
...


Some organs are innervated by just 1 division, but most vital organs receive

Dual innervation) receiving instructions from both divisions
...

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Chapter 16:

Anatomy of Dual Innervation
Autonomic plexuses) a series of nerve networks formed by the mingling of the sympathetic
postganglionic fibers and parasympathetic preganglionic fibers, which takes place in the thoracic and
abdominopelvic cavities
...


↓
➢
➢
➢
➢
➢
➢

Cardiac plexus:
Pulmonary plexus:
Esophageal plexus:
Celiac plexus:
Inferior mesenteric plexus:
Hypogastric plexus:

Autonomic Tone
Autonomic tone) the background level of activity, even without stimulation to autonomic motor
neurons showing a resting level of spontaneous activity
...

Consensual reflex) constriction of the pupils when a light is shone in one of the eyes
...


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Chapter 16:

Visceral Reflexes
Visceral reflex arc) consists of a receptor, sensory neuron, processing center, and 2 visceral
motor neurons
...

They can be long reflexes or short reflexes

Long reflexes) are the autonomic equivalents of the polysynaptic reflexes
...


Short reflexes) bypass the CNS entirely
...

Short reflexes control very short motor responses with localized effects
...
The cerebral cortex is required for their performance
...
They involve both conscious and unconscious information processing
3
...
For this reason, higher-order functions
are subject to adjustment over time
...


Skill memories) are learned motor behaviors
...
(E
...
Playing piano, riding a bike, etc)
Continued on next page

11

Chapter 16:
There is 2 classes of memory:
1
...
Repetition helps to incorporate it to long-term memory
2
...

The 2 types of long-term memories
1
...

2
...


Memory consolidation) the conversion from short-term memory to long-term memory
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Nucleus basalis) a cerebral nucleus near the diencephalon, plays an uncertain role in memory
storage and retrieval
...


Most long-term memories are stored in the cerebral cortex
...
This definition is based
on function rather than structure
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States of Consciousness
A conscious individual is alert, and unconscious individual is not
...

Unconscious) can refer to conditions ranging from the deep, unresponsive state induced by
anesthesia before major surgery, to deep sleep, to the light drifting some students experience from
reading anatomy and physiology textbooks
...


Deep sleep: also called slow wave or non-REM (NREM) sleep) your entire body relaxes,
and activity at the cerebral cortex is at a minimum
...


Rapid eye movement (REM): active dreaming, BP and respiratory rate change
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Reticular activation system (RAS) one of the most important brain stem components, this
network extends from the medulla oblongata to the midbrain
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16-9
Neurotransmitters influence brain chemistry and behavior
Changes in 2 or more neurotransmitters can profoundly affect brain function

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