#14 Sympathetic Nervous System

Your sympathetic nervous system is the part of your nervous system that responds to stress, and it does its job exceedingly well by focusing on what your body needs to do right now.
Your sympathetic nervous system sweeps these suddenly trivial functions aside to blast all of your energy to your brain and heart and muscles to deal with the threat at hand.
Physiological responses to non-immediate stresses are largely the same as when you're fighting for survival.

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<How Signals Travel to Effectors>
Each neuron travels from its root in the spinal cord to a ganglion, where it synapses - and that is a verb as well - with another nerve fiber.

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<Hormones & Neurotransmitters Communicate Stress>
The stress response includes two kinds of chemicals, both of which I'm sure you've heard of.
The first, of course, are neurotransmitters.
These are made and released from neurons themselves, and like we talked about in our lesson about synapses, they are what neurons use to communicate with each other - or their effector organs - across a synapse.
The other chemicals involved in stress are hormones, which are secreted by your glands.
The very same substance can have different effects, actually, sometimes, totally opposite effects depending on where it's received in your body.

Neurotransmitters:
products of nervous tissue

Hormones:
products of epithelial tissue

A compound can be considered either a neurotransmitter or a hormone.

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<Preganglionic Fibers Release Acetylcholine>
Your brain sends action potentials down your spinal cord and preganglionic neuronal axons.
Those signals flow all the way to their ganglia.
When the signals reach the synapses inside the ganglia, the nerve fibers then release a neurotransmitter - called acetylcholine, known to its friends as ACh.
ACh is really the coin of the realm.

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<Postganglionic Fibers Release Norepinephrine>
Those postganglionic neurons then carry the action potential to the effector organs - in this case, let's say your leg muscles, which are going to need an influx of blood if they're going to hustle you out of that house.
This one's called norepinephrine. And it is always norepinephire that's released from postganglionic fibers in the sympathetic nervous system.

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<Adrenal Glands Release Norephinephrine and Epinephrine as Hormones>
Like all preganglionic fibers, these release actylcholine.
The signal doesn't end up in another neuron that triggers blood, vessels to open or whatever.
The adrenal glands release norepinephrine as a hormone.

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<Neurotransmitters vs. Hormones>
Norepinephrine is both a neurotransmitter and a hormone, and which one it is depends on how it's being used.
Hormonal norepinephrine is just as good as neurotransmitter norepinephrine.
We describe them differently, because they're functioning differently.

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<How Norephinephrine Works: Alpha and Beta Receptors>
In the case of norepinephrine, its effector is smooth muscle - the muscle that controls all of your involuntary functions of hollow argans, like the stomach, and bladder, all of your involuntary functions of hollow organs, like the stomach, and bladder, and also your blood vessels.
You want those blood vessels to relax, and provide plenty of oxygen to the muscles in your arms and legs.
Throwing parts of your body into overdrive, while depriving others of blood and oxygen.
The frequent activation of your sympathetic nervous system, and the triggering the other part of your stress response -the part that's driven by hormones - can have nasty consequences, like high blood pressure, digestive problems, and even the supperssion of your immune system.
That is where your sympathetic system's more mellow half-brother, the parasympathetic system comes in.