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If you're taking anatomy and have tried to memorize the nerves of the abdomen/thorax, you may find this email our anatomy profs sent out as amusing as I did.
We would like to enlist your help in finding a cure for the dreaded disease, FOS (fear of splanchnics). As you know, this is an affliction that normally strikes healthy, young, intelligent, first year medical students. Symptoms include nightmares, uncontrollable screaming and hair pulling, and the look of fear when the word splanchnic is mentioned. Sadly, there is no known cure; symptoms, however, disappear spontaneously, usually after the first anatomy exam and ingestion of a large amount of a recreational beverage of choice.
Since Penn is an institution renowned for its research, we are offering a trial in a new therapy for FOS. Please read the attached information and let us know if the material decreases your symptoms.
Splanchnics
1. The term splanchnic nerve refers to a nerve that innervates viscera (organs). They are mixed nerves which contain both motor and sensory fibers. We will, however, only talk about the motor division. Because of the targets innervated, a splanchnic nerve must be an autonomic nerve. However, keep the following in mind;
a. A splanchnic nerve can be either sympathetic or parasympathetic.
b. A splanchnic nerve can be either preganglionic or postganglionic
c. Although all autonomic paths from spinal cord to target organ involve two nerves in series, only one of those nerves usually gets the name splanchnic; and it can be either the postganglionic OR the preganglionic fiber. The other nerve in the series is not named.
d. The term splanchnic can be used generically, i.e. any nerve that goes to viscera, or specifically as a name of a nerve (e.g. the greater splanchnic nerve).
e. The term is arbitrary; and some nerves that go to viscera, like the vagus nerve, should be called splanchnic but are not given that name.
f. Regardless of their name, all preganglionic autonomic fibers are myelinated (and look white) while all postganglionic autonomic nerves are non-myelinated and look gray.
2. There are 3 general classes of splanchnics:
a. preganglionic parasympathetic splanchnics
b. preganglionic sympathetic splanchnics
c. postganglionic sympathetic splanchnics
3. Sympathetic splanchnics:
a. Generically, there are thoracic, lumbar, and sacral preganglionic, sympathetic splanchnics. The preganglionic sympathetic fibers enter the sympathetic chain via white rami communicantes, as do all sympathetic nerves. However, rather than synapsing on the paravertebral ganglia in the chain, they leave the chain and synapse at the prevertebral ganglia, such as the celiac, SMA and IMA ganglia. It is the preganglionic fibers that get the name splanchnic. The postganglionic fibers in this situation are not named. Some of these preganglionic splanchnics (the ones from the thoracic region) have specific names: greater (from T5-T9), lesser (T10 and T11), and least splanchnic (T12) nerves. The others are just called lumbar and sacral splanchnics.
b. T1-T4 contribute sympathetic fibers to the postganglionic sympathetic splanchnics. The preganglionic fibers from T1-T4 enter the sympathetic chain as usual, through white rami communicantes, and synapse on the paravertebral ganglia. However, rather than exiting the sympathetic chain via gray rami communicantes, many of these fibers exit directly, dont enter a spinal nerve, and go directly to the lungs and heart. These postganglionic sympathetic nerves are specifically called the cardiopulmonary splanchnics. In this case, the preganglionic fibers are not named.
4. Parasympathetic splanchnics
a. The one group of parasympathetic splanchnics are preganglionic parasympathetic splanchnics and are called the pelvic splanchnic nerves. These fibers have nothing to do with the sympathetic trunk. They are derived directly from the ventral rami of S2-S4 and synapse in ganglia in the inferior hypogastric plexus, or in the wall of the bladder and hindgut. The postganglionic fibers are in the descending and sigmoid colons and rectum and bladder. The postganglionic fibers are not named.
We would like to enlist your help in finding a cure for the dreaded disease, FOS (fear of splanchnics). As you know, this is an affliction that normally strikes healthy, young, intelligent, first year medical students. Symptoms include nightmares, uncontrollable screaming and hair pulling, and the look of fear when the word splanchnic is mentioned. Sadly, there is no known cure; symptoms, however, disappear spontaneously, usually after the first anatomy exam and ingestion of a large amount of a recreational beverage of choice.
Since Penn is an institution renowned for its research, we are offering a trial in a new therapy for FOS. Please read the attached information and let us know if the material decreases your symptoms.
Splanchnics
1. The term splanchnic nerve refers to a nerve that innervates viscera (organs). They are mixed nerves which contain both motor and sensory fibers. We will, however, only talk about the motor division. Because of the targets innervated, a splanchnic nerve must be an autonomic nerve. However, keep the following in mind;
a. A splanchnic nerve can be either sympathetic or parasympathetic.
b. A splanchnic nerve can be either preganglionic or postganglionic
c. Although all autonomic paths from spinal cord to target organ involve two nerves in series, only one of those nerves usually gets the name splanchnic; and it can be either the postganglionic OR the preganglionic fiber. The other nerve in the series is not named.
d. The term splanchnic can be used generically, i.e. any nerve that goes to viscera, or specifically as a name of a nerve (e.g. the greater splanchnic nerve).
e. The term is arbitrary; and some nerves that go to viscera, like the vagus nerve, should be called splanchnic but are not given that name.
f. Regardless of their name, all preganglionic autonomic fibers are myelinated (and look white) while all postganglionic autonomic nerves are non-myelinated and look gray.
2. There are 3 general classes of splanchnics:
a. preganglionic parasympathetic splanchnics
b. preganglionic sympathetic splanchnics
c. postganglionic sympathetic splanchnics
3. Sympathetic splanchnics:
a. Generically, there are thoracic, lumbar, and sacral preganglionic, sympathetic splanchnics. The preganglionic sympathetic fibers enter the sympathetic chain via white rami communicantes, as do all sympathetic nerves. However, rather than synapsing on the paravertebral ganglia in the chain, they leave the chain and synapse at the prevertebral ganglia, such as the celiac, SMA and IMA ganglia. It is the preganglionic fibers that get the name splanchnic. The postganglionic fibers in this situation are not named. Some of these preganglionic splanchnics (the ones from the thoracic region) have specific names: greater (from T5-T9), lesser (T10 and T11), and least splanchnic (T12) nerves. The others are just called lumbar and sacral splanchnics.
b. T1-T4 contribute sympathetic fibers to the postganglionic sympathetic splanchnics. The preganglionic fibers from T1-T4 enter the sympathetic chain as usual, through white rami communicantes, and synapse on the paravertebral ganglia. However, rather than exiting the sympathetic chain via gray rami communicantes, many of these fibers exit directly, dont enter a spinal nerve, and go directly to the lungs and heart. These postganglionic sympathetic nerves are specifically called the cardiopulmonary splanchnics. In this case, the preganglionic fibers are not named.
4. Parasympathetic splanchnics
a. The one group of parasympathetic splanchnics are preganglionic parasympathetic splanchnics and are called the pelvic splanchnic nerves. These fibers have nothing to do with the sympathetic trunk. They are derived directly from the ventral rami of S2-S4 and synapse in ganglia in the inferior hypogastric plexus, or in the wall of the bladder and hindgut. The postganglionic fibers are in the descending and sigmoid colons and rectum and bladder. The postganglionic fibers are not named.
