The autonomic nervous system controls involuntary homeostatic mechanisms
that control target cells in exocrine and endocrine glands, smooth muscle in the
intestine and blood vessels, and cardiac muscle. The A.N.S. is directly regulated
by the medulla and hypothalamus and indirectly by the limbic system. See pg 533.

Sympathetic Nervous System - See page 535-542.

"Sympathetic" means sympathetic to flight-fight activities. It is also called the
thoraco-lumbar system because its nerve processes from the spinal cord proceed
via the thoracic and lumbar spinal nerves and rami communicantes to the collateral
sympathetic trunks and associated ganglia. Ascending towards the neck are the
inferior (largely to the heart), middle (to the heart) and superior (to the eye,
nasal cavities, and the salivary glands) cervical ganglia. In the abdominal
cavities the Sympathetic N.S. communicates with to the kidneys, liver, and
stomach through the greater splanchnic nerve and on through the celiac ganglion.
The superior mesenteric ganglion controls the ascending colon, transverse
colon and the small intestine.
-

Label the sympathetic ganglia in the neck.

The lumbar splanchnic nerve connects to the inferior mesenteric ganglion to
send sympathetic impulses to the genitals, urinary bladder, descending colon, and rectum.

The Sympathetic N.S. conducts those involuntary activities which tend to enhance
one's Flight-Fight response, i.e, widespread vasoconstriction to increase blood pressure,
bronchial dilation, heart rate increase (particularly with the release of epinephrine
(adrenaline) and norepinephrine from the adrenal gland, and vasodilation to certain
blood vessels serving the heart and lungs (again with epinephrine and norepinephrine),
the effect locally is to increase blood volume to these organs), and vasoconstriction to
the gut (locally decreasing blood volume, where its not needed). The Sympathetic N.S.
is also responsible for orgasm as it kicks in to homeostatically balance the stimulation
of the Parasympathetic N.S.

Parasympathetic N.S. (See pg. 535) - also called the cranio-sacral system because
it consists of various cranial nerves and sacral nerves. The Oculomotor nerve (III) sends
parasympathetic impulses to the eye. The Facial nerve (VII) sends impulses to
the tear glands and nasal cavities, the Glossopharyngeal nerve (IX) directs
salivary glands under the tongue, and the major "motor" of the Parasympathetic N.S.,
the Vagus nerve (X) sends branches to the larynx, heart, and most of the gut.
The sacral nerves send branches to the rectum, urinary bladder and genitals via
the pelvic splanchnic nerves. The Parasympathetic N.S. controls activities of
digestion, relaxation and sexual arousal.  It is responsible for defecation and
urination reflexes.  Where parasympathetic impulses to the stomach are overactive,
ulcers may result from increased acid secretions (although 70% of ulcers are due
to bacterial infections).  Where parasympathetic ganglia are genetically absent or
destroyed by parasites, a greatly enlarged flaccid megacolon may result.

Why was cutting the vagus branch to the stomach (vagotomy) used to treat
chronic ulcers?

A.N.S. neurotransmitters include Ach (from cholinergic neurons) for the
Parasympathetic N.S. and Ach, epinephrine and norepinephrine
(from adrenergic neurons) for the Sympathetic N.S.  Ach is a sympathetic
neurotransmitter for most sweat glands, tear glands, and the adrenal glands.

The receptors for Ach are nicotinic (stimulated by Ach and nicotine),
muscarinic (stimulated by the mushroom poison muscarine, and, of course, Ach).
The symptoms of toad stool poisoning include tearing, slowing of the heart,
and increased salivary secretions. Why? See p. 545, Table 14.3 and table 14.4., and 14.5, p. 546.
See http://familydoctor.org/handouts/129.html
 
 

CNS System	Peripheral N.S. Effectors	Neurotransmitter/Receptor  (postganglionic if applicable
Somatic	long axon in spinal nerve to  skeletal muscle	Ach/nicotinic
Sympathetic	long axon in spinal nerve to the adrenal gland	Ach/nicotinic stimulates secretion of Epinephrine (alpha & beta)  & Norepinephrine (alpha, mostly)
Sympathetic	chain & collateral ganglia to heart, sweat glands	Ach-nicotinic in ganglion, NE secreted by postganglionic neuron.
Parasympathetic	terminal ganglion in glands, smooth muscle of  gut	Ach-nicotinic/preganglionic to postganglionic neuron. Ach-muscarinic/ postganglionic neuron to effector (may be in target organ).

Norepinephrine acts mostly on alpha receptors, causing generalized sympathetic peripheral
vasoconstriction that raises blood pressure. NE binding to alpha receptors in the arteries
of the skin and gut result in reduced blood flow to those organs and decreased motility
of gut smooth muscle. NE binding to beta receptors in the lung arteries and heart muscle
arteries results in relaxation of smooth muscle and therefore vasodilation, resulting in
more blood flow to those organs. In the lungs and heart, sympathetic Ep/NE binding to
causes airway dilation. Many asthmatic medication mimic these neurotransmitters. Why
do some kids die of heart attacks while taking these medications? See below. NE is also
a metabotropic hormone - one which has long-lasting effects on target cells by increasing
their metabolism.

In the heart, binding of Epinephrine to alpha and beta₁ receptors increases heart rate
and force of blood ejection. Binding to beta₂  receptors  receptors in the blood vessels
of the heart and lungs causes relaxation of smooth muscle and therefore vasodilation.
The same applies to the bronchioles under sympathetic stimulation. NE binds to beta
receptors in heart/cardiac muscle and to the pacemaker to increase stroke volume, and
rate respectively. For heart patients who have irregular heartbeats and high heart rates,
beta blockers such as Inderal are prescribed.

Parasympathetic secretions of Ach on heart muscle slow and weaken its force.
Parasympathetic secretions of Ach causes vasodilation in the salivary glands and
increases gut motility and secretions.

The A.N.S. may be strongly controlled by the limbic system and hypothalamus
under conditions of emotional stress. The A.N.S. may increase heart rate (sympathetic)
or cause fainting (inhibiting vasoconstriction) by causing massive vasodilation.  Levels
of steroid hormones increase that lead to heart disease and high blood pressure.

Mass or autonomic dysreflexia syndrome is an epilepsy of the spinal cord and
sympathetoic trunks. Neural depolarizations spread up the sympathetic trunks to the
cervical ganglia that greatly increase heart rate and blood pressure. Strokes result.
This is seen in quadriplegics like General George Patton as a result of an automobile
accident following World War II. They didn't have seat belts then. Some odd stimulus
like a puff of air or a full bladder sets off the autonomic reflex.  Remember
that the connection with the brain is not there to control the spreading depolarizations,
but to dampen them.

Study Questions

1. You sit down for a relaxing dinner. Explain the physiological changes that now occur.
2. A bear invades your camper at Yellowstone looking for the Salmon you just grilled.
Explain the physiological changes that now occur.
3. Explain the addictive aspects of nicotine. What parts of the CNS and PNS have
nicotinic receptors?
4. Explain the symptoms of muscarine/toadstool mushroom poisoning.
 
 

e-mail:jaliff @ gpc.edu