General visceral afferent fiber
General visceral afferent fibers | |
---|---|
Sympathetic efferent. 6,7. Autonomic nervous system (ANS) afferent. This image merely depicts pathways in a schematic fashion – it is not anatomically correct. The efferent sympathetics exit in a loop. | |
Anatomical terminology] |
The general visceral afferent (GVA) fibers conduct sensory impulses (usually pain or reflex sensations) from the
GVA fibers create referred pain by activating general somatic afferent fibers where the two meet in the posterior grey column.
The
Generally, they are insensitive to cutting, crushing or burning; however, excessive tension in smooth muscle and some pathological conditions produce visceral pain (referred pain).[4]
Pathway
Abdomen
In the abdomen, general visceral afferent fibers usually accompany sympathetic efferent fibers. This means that a signal traveling in an afferent fiber will begin at sensory receptors in the afferent fiber's target organ, travel up to the ganglion where the sympathetic efferent fiber synapses, continue back along a
The only GVA nerves in the abdomen that do not follow the above pathway are those that innervate structures in the distal half of the sigmoid colon and the rectum. These afferent fibers, instead, follow the path of parasympathetic efferent fibers back to the vertebral column, where the afferent fibers enter the S2-S4 sensory (dorsal root) ganglia followed by the spinal cord.[5]
Pelvis
The course of GVA fibers from organs in the pelvis, in general, depends on the organ's position relative to the pelvic pain line. An organ, or part of an organ, in the pelvis is said to be "above the pelvic pain line" if it is in contact with the peritoneum, except in the case of the large intestine, where the pelvic pain line is said to be located in the middle of the sigmoid colon.[6] GVA fibers from structures above the pain line follow the course of the sympathetic efferent fibers, and GVA fibers from structures below the pain line follow the course of the parasympathetic efferents.[6] Pain from the latter fibers is less likely to be consciously experienced.[6]
Neurotransmitters
For many of these visceral afferents, their endings in the periphery and in the spinal cord contain substance P and other neuropeptides of the tachykinin family, such as neurokinin A and neurokinin B, specifically in the sympathetic portion of these fibres.[7]
See also
- General visceral efferent fiber (GVE)
- Referred pain
- General somatic afferent fiber (GSA)
- Special somatic afferent fiber(SSA)
- Special visceral afferent fiber (SVA)
References
- ISBN 978-0-7817-6274-8.
- ^ ISBN 978-0-7817-6274-8.
- ^ Mehta, Samir et al. Step-Up: A High-Yield, Systems-Based Review for the USMLE Step 1. Baltimore, MD: LWW, 2003.
- OCLC 920806541.
- ^ ISBN 978-0-7817-6274-8
- ^ ISBN 978-0-7817-6274-8.
- PMID 8685245.