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ANS - The Sympathetic SYSTEM
The Autonomic Nervous System
The autonomic nervous system (ANS) regulates the
functions of our internal organs (the viscera) such as the
heart, stomach and intestines. The ANS is part of the
peripheral nervous system and it also controls some of
the muscles within the body. We are often unaware of
the ANS because it functions involuntarily and reflexively.
However, some people can be trained to control some
functions of the ANS such as heart rate or blood pressure.
The ANS is most important in two situations:
• In emergencies that cause stress and require us to
"fight" or take "flight" (run away)
• In non emergencies that allow us to "rest" and "digest."
REST AND DIGEST
TAKE FLIGHT
The ANS regulates:
• Muscles
• - in the skin (around hair follicles; smooth muscle)
- around blood vessels (smooth muscle)
- in the eye (the iris; smooth muscle)
- in the stomach, intestines and bladder (smooth
muscle)
- of the heart (cardiac muscle)
• Glands
• The ANS is divided into three parts:
a) The sympathetic nervous system
b) The parasympathetic nervous system
c) The enteric nervous system
The Sympathetic Nervous System
As we notice in the picture, the sympathetic nervous
system originates in the spinal cord. Specifically, the
cell bodies of the first neuron (the preganglionic
neuron) are located in the thoracic and lumbar spinal
cord. Axons from these neurons project to a chain of
ganglia located near the spinal cord. In most cases,
this neuron makes a synapse with another neuron
(post-ganglionic neuron) in the ganglion. A few
preganglionic neurons go to other ganglia outside of
the sympathetic chain and synapse there. The postganglionic neuron then projects to the "target" either a muscle or a gland.
The fight or flight response
Situation: It is a nice, sunny day...I’m going on a nice
walk in the woods. Suddenly, a fierce boar appears in
front of me.
What shall I do? Stay and fight OR run away?
These are "Fight or Flight" responses. In these types
of situations, the sympathetic nervous system is
called into action - it uses energy - so blood pressure
increases, heart beats get faster, and digestion slows
down.
Neurotransmitters
The synapse in the sympathetic ganglion uses
acetylcholine as a neurotransmitter; the synapse of
the post-ganglionic neuron with the target organ uses
the neurotransmitter called norepinephrine.
Acetylcholine
• Acetylcholine (often abbreviated ACh) is the most
common neurotransmitter. It is located in both the
central nervous system (CNS) and the peripheral
nervous system (PNS).
• Acetylcholine was the first neurotransmitter to be
identified. It was discovered by Henry Hallett Dale in
1914 and its existence was later confirmed by Otto
Loewi. Both individuals were awarded the Nobel Prize
in Physiology in 1936 for their discovery.
Norepinephrine
Norepinephrine is both a neurotransmitter and a hormone. It is a catecholamine (a)
produced by the (b) adrenal glands using (c) dopamine as a starting point.
• (a) Catecholamines are a type of hormone known to strongly affect blood pressure
by acting on the blood vessels and the heart. They are made from the amino acid
tyrosine. Illness and certain types of cancers can increase the level of catecholamines
in the body, leading to elevations in blood pressure and heart rate.
• (b) The adrenal glands are small, triangle- or pyramid-shaped organs found near the
top of each kidney. There are two adrenal glands - one on each side of the body. The
adrenal glands produce a variety of hormones involved in stress reactions, blood
pressure regulation, and the handling of vitamins and minerals. Certain types of
adrenal gland problems can cause an increase in hormone release, leading to elevated
blood pressure, rapid heart beat, or high/low levels of minerals and/or nutrients.
• (c) Dopamine is a body chemical that plays important roles at several locations in the
body.
Dopamine levels are high in the brain, where it is necessary for:
- Learning
- Mood regulation
- Information processing/integration
Dopamine can also be given intravenously as a medication. In this capacity, it acts as a
stimulant on the cardiovascular system and results in increased heart rate, increased
blood pressure, and increased blood flow. Dopamine given this way does not affect the
brain. Dopamine is the root chemical the body uses to synthesize catecholamines.
The parasympathetic nervous system
In the picture the cell bodies of the parasympathetic
nervous system are located in the spinal cord (sacral
region) and in the medulla. In the medulla, the cranial
nerves III, VII, IX and X form the preganglionic
parasympathetic fibers. The preganglionic fiber from
the medulla or spinal cord projects to ganglia very
close to the target organ and makes a synapse. This
synapse
uses
the
neurotransmitter
called
acetylcholine. From this ganglion, the post-ganglionic
neuron projects to the target organ and uses
acetylcholine again at its terminal.
The rest and digest response
Situation: It is a bright, summer day...John is playing
on the sand with Richard, his son, while Margie, his
wife, is sitting on a beach towel in total relax. After
some time, John decides to sit on a chair to relax, too.
This calls for "Rest and Digest" responses. Now it is
the time for the parasympathetic nervous to work to
save energy. This is when blood pressure can
decrease, pulse rate can slow, and digestion can start.
The restless activity of ANS
It should be noted that the autonomic nervous system
is always working. It is NOT only active during "fight or
flight" or "rest and digest" situations. Rather, the
autonomic nervous system acts to maintain normal
internal functions and works with the somatic
nervous system.
The enteric nervous system is a third division of the
autonomic nervous system. It is a meshwork of nerve
fibers that innervate the viscera (gastrointestinal
tract, pancreas, and gall bladder).
The Enteric Nervous System
Summing up: the effects of sympathetic and parasympathetic
stimulation
Structure
Sympathetic Stimulation
Parasympathetic Stimulation
Iris (eye muscle)
Pupil dilation
Pupil constriction
Salivary Glands
Saliva production reduced
Saliva production increased
Oral/Nasal Mucosa
Mucus production reduced
Mucus production increased
Heart
Heart rate and force increased
Heart rate and force decreased
Lung
Bronchial muscle relaxed
Bronchial muscle contracted
Stomach
Peristalsis reduced
Gastric juice secreted; motility
increased
Small Intestine
Motility reduced
Digestion increased
Large Intestine
Motility reduced
Secretions and motility increased
Liver
Increased conversion of
glycogen to glucose
Kidney
Decreased urine secretion
Adrenal medulla
Norepinephrine and
epinephrine secreted
Bladder
Wall relaxed
Sphincter closed
Increased urine secretion
Wall contracted
Sphincter relaxed
Two effects of the sympathetic/parasympatetic
stimulations
a) DILATED PUPIL
(an effect of the sympathetic
stimulation)
b) SALIVA PRODUCTION INCREASED
(an effect of the parasympathetic
stimulation)
LICEO SCIENTIFICO STATALE
«G. GALILEI»
Pescara
A.S. 2014-15
UDA CLIL: The Sympathetic/Parasympathetic
Systems and Humour
English Teacher: Miscia Roberta
Class: III A