Autonomics of the gut Flashcards
What fibers can be found in an autonomic plexus?
Pre and post synaptic sympathetic fibers, pre-synaptic parasympathetic fibers, and afferent fibers.
Where are the post-synaptic parasympathetic fibers?
In the walls of the target organ.
What is the general effect of parasympathetic action?
Stimulate glandular secretion and peristalsis, as well as cause relaxation of sphincters.
What is the general effect of sympathetic action?
Constrict sphincters, increases vasomotor tone, and decrease glandular secretion.
What do afferents (GVA) that travel with parasympathetics convey?
Hunger, nausea, stretch/distension, and contribute to visceral reflexes.
What do afferents (GVA) that travel with sympathetics convey?
Acute pain from the viscera.
Where are the abdominal autonomic plexuses located?
They course on the surface of the aorta and its branches.
What do abdominal autonomic plexuses contain?
preganglionic fibers from splanchnic nerves and post-ganglionic sympathetic fibers which originate in pre-vertebral ganglia. Also pre-ganglionic parasympathetic fibers.
What ANS plexus innervates the foregut?
The celiac plexus. Distributes via the celiac trunk artery.
What ANS plexus innervates the midgut?
The superior mesenteric plexus. Distributes via branches of the SMA.
What ANS plexus innervates the hindgut?
The inferior mesenteric plexus. Distributes via branches of the IMA.
What nerve provides parasympathetic fibers to the foregut and midgut?
The Vagus nerve.
Where are pre-ganglionic cells bodies of the Vagus located?
In the brainstem (dorsal motor nucleus).
Where does the Vagus nerve enter the abdomen?
At the esophageal hiatus (T10).
What provides parasympathetic fibers to the hindgut?
Pelvic splanchnic nerves.
Where are the pre-ganglionic cell bodies of the pelvic splanchnic nerves located?
In the IML horns of S2-S4 spinal cord.
How do pre-ganglionic fibers of pelvic splanchnic nerves travel from the spinal cord?
They travel with ventral rami of S2-S4 spinal nerves and then exit the nerve as pelvic splanchnic nerves in the pelvis.
Where are the pre-ganglion cell bodies of sympathetics to the abdominal viscera located?
In the T5-L2 spinal cord.
How do the pre-ganglionic sympathetic fibers exit the spinal cord?
They enter the sympathetic chain and then exit as splanchnic nerves which enter the aortic plexuses.
Do pre-ganglion sympathtetics synapse in the sympathetic chain?
No. They only travel through without synapsing (what makes them splanchnic nerves). Boards will try and trick you on this.
What happens after pre-ganglionic sympathetics enter aortic plexuses?
They synapse with post-ganglionic neurons in various pre-vertebral ganglia. These post-ganglionic fibers then distribute via aortic plexuses.
What splanchnic nerve provides sympathetic innervation to the foregut?
The greater splanchnic nerve.
What splanchnic nerves provide sympathetic innervation to the midgut?
The greater, lesser, and least splanchnic nerves. (also to the kidney in the case of the lesser and least)
What splanchnic nerve provides sympathetic innervation to the hindgut?
The lumbar splanchnic nerves.
