Sympathetic and Parasympathetic Nervous Systems

EHS unit 4

Learning Targets• Describe the opposing functions of

the parasympathetic and sympathetic divisions of the autonomic nervous system.

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.

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

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.

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.

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).

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.

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”

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.