Now, the sympathetic nervous sytem, this
is the kind of fight or flight response.
Here you’re trying to decrease secretions,
decrease motility, increase constriction
of the sphincter and decrease blood flow.
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.
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.
Where do the nerves
come off here?
These almost all come off either the thoracic
or the lumbar region of the spinal cord.
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.
So parasympathetic, sympathetic systems
are very important in undergoing
the digestion or stopping
digestion from occurring.
Now the control of blood flow also has
parasympathetic and sympathetic components.
The parasympathetic control of
blood flow is to increase it.
So what does it utilize
to increase blood flow?
There are two primary
neurotransmitters associated with
increasing blood flow to the
The first is acetylcholine and the
second is vasoactive intestinal peptide.
Both of these are released from
the parasympathetic nerves
and vasodilate or increase the
luminal size of the blood vessels.
The sympathetic nervous does the opposite
with two different neurotransmitters.
It does it through
norepinephrine and ATP.
Both causing vasoconstriction or decreasing
the luminal diameter of the blood vessel.
But I mentioned that there’s a lot of
local reflexes involved in the GI system.
So with the enteric nervous system,
there are these local reflexes
that also increase the
amount of acetylcholine and
vasoactive intestinal peptide
The last way is something that’s
more conscious in nature.
And these particular neurons secrete
calcitonin gene-related peptide
and substance P to cause a
small amount of vasodilation.
So acetylcholine vasoactive intestinal
peptide cause large vasodilation.
Calcitonin-gene related peptide and
substance P, small amount of vasodilation.
This is the only component
of the sensory system
that you will probably
have conscious knowledge.
So the information will
be sent back to brain
and you may feel full or feel distended.
While in the previous example,
those are local reflexes,
and those you probably don’t
have conscious perception of.