1. health and fitness
2. exercise

9.4 Homeostasis and the
Autonomic Nervous System
• All autonomic nerves
are motor nerves that
regulate organs
without conscious
control
• Motor nerves lead to
muscles that are
controlled by
conscious control
•
The autonomic
nervous system
maintains
homeostasis by
adapting your body
to the external
environment
• Composed of two
distinct units:
1. Sympathetic
Nervous System
2. Parasympathetic
Nervous System
Sympathetic system
• Prepares the body for stress
Parasympathetic system
• Restores normal body condions
Sympathetic Nerves:
• Come from the
thoracic vertebrae,
and lumbar vertebrae
Parasympathetic
Nerves:
• Exit directly from the
brain, or either the
cervical, or caudal
sections of the spinal
cord
Vagus nerve
• major cranial
nerve
• parasympathetic
• Branches of the
vagus nerve
regulate the
heart, bronchi,
liver, pancreas,
and digestive
tract
Some Effects of the Autonomic Nervous System
Organ
Sympathetic
Parasympathetic
Heart
Increase heart rate
Decrease heart rate
Digestive
Decrease peristalsis
Increase peristalsis
Liver
Stores glucose
Eyes
Increases the release of
glucose
Dilates pupils
Constricts pupils
Bladder
Relaxes sphincter
Contracts sphincter
Skin
Increases blood flow
Decreases blood
flow
Adrenal gland
Causes the release of
epinephrine
No effect
Natural Painkillers
• Pain is interpreted in the substantia gelatinosa
(SG) – grey matter in the dorsal spinal cord
• Upon stimulation, the SG produes a
neurotransmitter that “informs” the injured tissue
or organ of the damage
• The greater the amount of the pain
neurotransmitter attached to the organ, the
greater the perception of pain
• Endorphins and Enkephalins attach to receptor
sites in the SG
Endorphins
They are produced by the
pituitary gland and the
hypothalamus during strenuous
exercise, excitement, pain, death,
and orgasm,
they resemble the opiates in their
abilities to produce analgesia
and a sense of well-being.
Endorphins work as "natural
pain relievers", whose effects
may be enhanced by other
medications.
Endorphins
• Natural painkillers produced by the brain
• They work by occupying sites in the
substantia gelatinosa (SG) of the brain,
which are normally used by pain-signalling
chemicals. The endorphins block the
sites, reducing the intensity of the pain.
Endorphins
• endorphins ("endogenous morphine") are one
of several morphine-like substances (opioids)
that occur within our brains. Their molecular
structure is very similar to morphine but with
different chemical properties.
• Endorphins are polypeptides containing 30
amino acid units. They are manufactured by the
body to reduce stress and relieve pain.
• Usually produced during periods of extreme
stress, endorphins naturally block pain signals
produced by the nervous system.
• The human body produces at least 20 different
endorphins
• Beta- endorphin appears to be the endorphin
that seems to have the strongest affect on the
brain and body during exercise.
• Prolonged, continuous exercise like running,
long-distance swimming, aerobics, cycling or
cross-country skiing appears to contribute to an
increased production and release of
endorphins. This results in a sense of euphoria
that has been popularly labeled the "runner's
high."
• Chocolate is by far the most popular endorphinproducing food on Earth.
• In addition to sugar, caffeine and fat, chocolate
contains more than 300 different constituent
compounds, including anandamide, a chemical that
mimics marijuana's soothing effects on the brain.
• It also contains chemical compounds such as
flavanoids (which are also found in wine) that have
antioxident properties and reduce serum cholesterol.
• Although the combined psychochemical effects of
these compounds on the central nervous system are
poorly understood, the production of endorphins are
believed to contribute to the renowned "inner glow"
experienced by dedicated chocolate lovers.
• endorphins are believed to produce four
key effects on the body/mind:
–they enhance the immune system,
–they relieve pain,
–they reduce stress,
–they postpone the aging process.
–Scientists also have found that betaendorphins can activate human NK
(Natural Killer) cells and boost the
immune system against diseases and
kill cancer cells.
Artificial Painkillers
• Opiates – i.e. heroin,
codeine, and morphine,
also attach to the SG
neurons, preventing
production and release of
Pain neurotransmitters
• Often produce feelings of
tranquality
• Intake of opiates can
reduce the production of
the body’s natural pain
killers
Depressants
i.e. Valium and Librium
• Enhance the action of
inhibitory synapses
• Synthesis of inhibitory
neurotransmitters often
increase in the presence
of depressants
• Alcohol, however, is
different, it does not act
directly on the synapse