This document describes the opposing functions of the parasympathetic and sympathetic nervous systems. The parasympathetic nervous system is responsible for "rest and digest" functions like slowing the heart rate and increasing digestion. It uses acetylcholine as a neurotransmitter. The sympathetic nervous system is responsible for the "fight or flight" response, increasing heart rate, blood pressure, and diverting blood flow away from digestion to muscles. It uses epinephrine, norepinephrine, and acetylcholine as neurotransmitters. Both systems work together to maintain homeostasis in the body.

1. Sympathetic and
Parasympathetic Nervous
Systems
EHS unit 4

2. Learning Targets
• Describe the opposing functions of the
parasympathetic and sympathetic
divisions of the autonomic nervous
system.

3. Autonomic Nervous System,
Review
• This is the automated system that controls
our vital functions.
– Modifies heart and respiratory rate
– Controls smooth muscles through out the
body
– Controls processes of digestive, urinary, and
reproductive systems.
– Controls functions of glands through out the
body.

4. Parasympathetic Nervous System
• The “rest and digest” or “feed and breed”
system.
– Opposed by the sympathetic nervous system.
• Major pathways:
– Cranial nerves III, VII, IX
– Vagus Nerve**
– Pelvic Splanchnic Nerve

5. Neurotransmitters in the PSNS
• The PSNS uses Acetylcholine as it’s
primary neurotransmitter.
– It is used to stimulate the smooth muscles in
the vital organs.
– Other chemicals used to stimulate excretion
are used as well.

6. Functions of the PSNS
• Again, Rest and Digest + Feed and Breed.
– This is the “chill” nervous system.
• It encourages our digestive and urinary tracts to do
their jobs by increasing blood flow to them.
• It increases secretion in the mucous membranes.
• Sexual response is rooted in this system.
• Heart rate and respirations are slowed to resting rates.
• Helps to initiate sleep.

7. Sympathetic Nervous System
• This is the “freak out” or “fight/flight”
response system.
– This system is in control when we perceive
danger, urgency, or anxiety.
• Major Pathways for this system:
– Sympathetic Pathways are primarily from T1
(thoracic) to L2 (lumbar).

8. Neurotransmitters of the SNS
• The SNS relies on several
neurotransmitters to functions.
– Epinephrine and Norepinephrine
(adrenalines)
Adrenaline is a hormone and a
neurotransmitter.
– ACH is also used to stimulate sweat glands,
etc.

9. Actions of the SNS
• Fight or Flight + Freak Out Response
– When we perceive a threat:
• Diverts blood away from the digestive,
reproductive, and urinary tracts to the muscles,
brain and heart.
• Slows mucous production.
• Increases heart and respiratory rate.
• Blood pressure increases
• Pupil dilate
• Sets our sensory receptors on “alert”

11. Working Together for Homeostasis
• At any given time, both systems are working. But,
one may be “in charge” in the moment.
– Sympathetic response is necessary for our survival. It
also feels exciting. We sort of like it and getting
amped up is healthy from time to time.
– Too much “fight or flight” means the body cannot
digest, rest, and heal effectively. It also makes the
heart work too hard. Long term stress can disrupt the
body’s function.
– Too much “rest and digest” makes us lethargic, under
stimulated, and can lead to weight gain or depression.