Neuroanatomy Questions

[lordman]

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Regarding splanchninc nerves, I wonder if two pathways are (efferent for sympathetic & another afferent for visceral pain ) in such a splanchnic nerve?

Regarding Splanchnic too, Thoracic Splanchnic nerves pass & synapse under diaphragm in the prevertebral ganglia to supply the Abdominal viscera & don't synapse in the paravertebral ganglia.
So how the Thoracic visceral pain fibers accompany these thoracic splanchinc nervers although the latter descend to the abdomen ??


Regarding Grey Ramii, since sympathetic nerves constitute the grey ramus....But the sympathetic distribution is the thoracolumbar T1-L2, i.e 14 in number.
Why there are 31 grey ramii ? What is the function of the remaining 17 (31-14=17) grey rami ??

 

[marqaha]

Here's what I think, but may need to be fact checked.

There are indeed both sympathetic efferent fibers and visceral afferent fibers within a single splanchnic nerve at its most proximal segment. The scenario you mentioned would require them separating. Visceral afferent axons do, in many cases, course through prevertebral ganglia without synapsing and travel within splanchnic nerves, through the paravertebral ganglia (again without synapsing), and terminate in spinal cord. Visceral afferent cell bodies are off course in the dorsal root ganglia with somatic afferent cell bodies.

The remaining 17 grey rami are post-ganglionic sympathetic axons from the neurons in the "extra" paravertebral ganglia. Even though pre-ganglionic sympathetic axons leave the spinal cord at only 14 levels, they can ascend or descend several levels within the sympathetic cord or chain (which is why they are sometimes called the sympathetic chain ganglia) before synapsing.

 

[lordman]

Thanks for reply 🙂