Sympathetic Nervous System – Gastrointestinal System

00:01 Now, the sympathetic nervous sytem, this is the kind of fight or flight response.

00:07 Here you’re trying to decrease secretions, decrease motility, increase constriction of the sphincter and decrease blood flow.

00:19 Because in a fight or flight response, what you want to do is to stop digesting just in case you might get digested by that lion.

00:30 So what you really want to do is to think about what kind of things you’d want to stop because they are less important at that particular time.

00:39 Where do the nerves come off here? These almost all come off either the thoracic or the lumbar region of the spinal cord.

00:46 And these will engage everything from the salivary glands, the upper part of the esophagus, And then you have a number of ganglia that are located in the GI system that will synapse the signal so that you get more information to the stomach, the small intestine, and the large intestine.

01:06 So parasympathetic, sympathetic systems are very important in undergoing the digestion or stopping digestion from occurring.

01:21 Now the control of blood flow also has parasympathetic and sympathetic components.

01:27 The parasympathetic control of blood flow is to increase it.

01:29 So what does it utilize to increase blood flow? There are two primary neurotransmitters associated with increasing blood flow to the gastrointestinal system.

01:39 The first is acetylcholine and the second is vasoactive intestinal peptide.

01:45 Both of these are released from the parasympathetic nerves and vasodilate or increase the luminal size of the blood vessels.

01:55 The sympathetic nervous does the opposite with two different neurotransmitters.

02:00 It does it through norepinephrine and ATP.

02:03 Both causing vasoconstriction or decreasing the luminal diameter of the blood vessel.

02:09 But I mentioned that there’s a lot of local reflexes involved in the GI system.

02:14 So with the enteric nervous system, there are these local reflexes that also increase the amount of acetylcholine and vasoactive intestinal peptide causing vasodilation.

02:24 The last way is something that’s more conscious in nature.

02:29 And these particular neurons secrete calcitonin gene-related peptide and substance P to cause a small amount of vasodilation.

02:37 So acetylcholine vasoactive intestinal peptide cause large vasodilation.

02:42 Calcitonin-gene related peptide and substance P, small amount of vasodilation.

02:48 This is the only component of the sensory system that you will probably have conscious knowledge.

02:54 So the information will be sent back to brain and you may feel full or feel distended.

03:00 While in the previous example, those are local reflexes, and those you probably don’t have conscious perception of.