General visceral afferent fiber

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General visceral afferent fibers
Gray799.svg
Scheme showing pathways of a typical spinal nerve.
1. Somatic efferent.
2. Somatic afferent.
3,4,5. 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 internal organs, glands, and blood vessels to the central nervous system. [1] They are considered to be part of the visceral nervous system, which is closely related to the autonomic nervous system, but 'visceral nervous system' and 'autonomic nervous system' are not direct synonyms and care should be taken when using these terms. Unlike the efferent fibers of the autonomic nervous system, the afferent fibers are not classified as either sympathetic or parasympathetic. [2]

Contents

GVA fibers create referred pain by activating general somatic afferent fibers where the two meet in the posterior grey column.

The cranial nerves that contain GVA fibers include the glossopharyngeal nerve (CN IX) and the vagus nerve (CN X). [3]

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 splanchnic nerve from the ganglion into the sympathetic trunk, move into a ventral ramus via a white ramus communicans, and finally move into the mixed spinal nerve between the division of the rami and the division of the roots of the spinal nerve. The GVA pathway then diverges from the sympathetic efferent pathway, which follows the ventral root into the spinal column, by following the dorsal root into the dorsal root ganglion, where the cell body of the visceral afferent nerve is located. [5] Finally, the signal continues along the dorsal root from the dorsal root ganglion to a region of gray matter in the dorsal horn of the spinal column where it is transmitted via a synapse to a neuron in the central nervous system. [2]

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

Related Research Articles

<span class="mw-page-title-main">Ganglion</span> Clusters of neurons in the peripheral nervous system

A ganglion is a group of neuron cell bodies in the peripheral nervous system. In the somatic nervous system, this includes dorsal root ganglia and trigeminal ganglia among a few others. In the autonomic nervous system, there are both sympathetic and parasympathetic ganglia which contain the cell bodies of postganglionic sympathetic and parasympathetic neurons respectively.

<span class="mw-page-title-main">Peripheral nervous system</span> Part of the nervous system excluding the brain and spinal cord

The peripheral nervous system (PNS) is one of two components that make up the nervous system of bilateral animals, with the other part being the central nervous system (CNS). The PNS consists of nerves and ganglia, which lie outside the brain and the spinal cord. The main function of the PNS is to connect the CNS to the limbs and organs, essentially serving as a relay between the brain and spinal cord and the rest of the body. Unlike the CNS, the PNS is not protected by the vertebral column and skull, or by the blood–brain barrier, which leaves it exposed to toxins.

<span class="mw-page-title-main">Autonomic nervous system</span> Division of the nervous system supplying internal organs, smooth muscle and glands

The autonomic nervous system (ANS), formerly referred to as the vegetative nervous system, is a division of the nervous system that operates internal organs, smooth muscle and glands. The autonomic nervous system is a control system that acts largely unconsciously and regulates bodily functions, such as the heart rate, its force of contraction, digestion, respiratory rate, pupillary response, urination, and sexual arousal. This system is the primary mechanism in control of the fight-or-flight response.

<span class="mw-page-title-main">Splanchnic nerves</span> Type of nerve in the human body

The splanchnic nerves are paired visceral nerves, carrying fibers of the autonomic nervous system as well as sensory fibers from the organs. All carry sympathetic fibers except for the pelvic splanchnic nerves, which carry parasympathetic fibers.

<span class="mw-page-title-main">Parasympathetic nervous system</span> Division of the autonomic nervous system

The parasympathetic nervous system (PSNS) is one of the three divisions of the autonomic nervous system, the others being the sympathetic nervous system and the enteric nervous system. The enteric nervous system is sometimes considered part of the autonomic nervous system, and sometimes considered an independent system.

<span class="mw-page-title-main">Sympathetic nervous system</span> Part of the autonomic nervous system which stimulates fight-or-flight responses

The sympathetic nervous system (SNS) is one of the three divisions of the autonomic nervous system, the others being the parasympathetic nervous system and the enteric nervous system. The enteric nervous system is sometimes considered part of the autonomic nervous system, and sometimes considered an independent system.

<span class="mw-page-title-main">Spinal nerve</span> Nerve that carries signals between the spinal cord and the body

A spinal nerve is a mixed nerve, which carries motor, sensory, and autonomic signals between the spinal cord and the body. In the human body there are 31 pairs of spinal nerves, one on each side of the vertebral column. These are grouped into the corresponding cervical, thoracic, lumbar, sacral and coccygeal regions of the spine. There are eight pairs of cervical nerves, twelve pairs of thoracic nerves, five pairs of lumbar nerves, five pairs of sacral nerves, and one pair of coccygeal nerves. The spinal nerves are part of the peripheral nervous system.

<span class="mw-page-title-main">Glossopharyngeal nerve</span> Cranial nerve IX, for the tongue and pharynx

The glossopharyngeal nerve, also known as the ninth cranial nerve, cranial nerve IX, or simply CN IX, is a cranial nerve that exits the brainstem from the sides of the upper medulla, just anterior to the vagus nerve. Being a mixed nerve (sensorimotor), it carries afferent sensory and efferent motor information. The motor division of the glossopharyngeal nerve is derived from the basal plate of the embryonic medulla oblongata, whereas the sensory division originates from the cranial neural crest.

<span class="mw-page-title-main">Afferent nerve fiber</span> Axonal projections that arrive at a particular brain region

Afferent nerve fibers are axons of sensory neurons that carry sensory information from sensory receptors to the central nervous system. Many afferent projections arrive at a particular brain region.

The dorsal longitudinal fasciculus (DLF) is a longitudinal tract interconnecting the posterior hypothalamus, and the inferior medulla oblongata. It contains both ascending tracts and descending tracts, and serves to link the forebrain, and the visceral autonomic centres of the lower brainstem. It conveys both visceral motor signals, and sensory signals.

<span class="mw-page-title-main">Geniculate ganglion</span> Collection of facial nerve neurons

The geniculate ganglion is a collection of pseudounipolar sensory neurons of the facial nerve located in the facial canal of the head. It receives fibers from the facial nerve. It sends fibers that supply the lacrimal glands, submandibular glands, sublingual glands, tongue, palate, pharynx, external auditory meatus, stapedius muscle, posterior belly of the digastric muscle, stylohyoid muscle, and muscles of facial expression.

<span class="mw-page-title-main">Sympathetic trunk</span>

The sympathetic trunks are a paired bundle of nerve fibers that run from the base of the skull to the coccyx. They are a major component of the sympathetic nervous system.

<span class="mw-page-title-main">White ramus communicans</span>

The white ramus communicans from Latin ramus (branch) and communicans (communicating) is the preganglionic sympathetic outflow nerve tract from the spinal cord.

<span class="mw-page-title-main">General visceral efferent fiber</span>

General visceral efferent fibers (GVE) or visceral efferents or autonomic efferents, are the efferent nerve fibers of the autonomic nervous system that provide motor innervation to smooth muscle, cardiac muscle, and glands through postganglionic varicosities.

<span class="mw-page-title-main">Sympathetic ganglia</span> Ganglia of the sympathetic nervous system

The sympathetic ganglia, or paravertebral ganglia, are autonomic ganglia of the sympathetic nervous system. Ganglia are 20,000 to 30,000 afferent and efferent nerve cell bodies that run along on either side of the spinal cord. Afferent nerve cell bodies bring information from the body to the brain and spinal cord, while efferent nerve cell bodies bring information from the brain and spinal cord to the rest of the body. The cell bodies create long sympathetic chains that are on either side of the spinal cord. They also form para- or pre-vertebral ganglia of gross anatomy.

Pelvic splanchnic nerves or nervi erigentes are splanchnic nerves that arise from sacral spinal nerves S2, S3, S4 to provide parasympathetic innervation to the organs of the pelvic cavity.

<span class="mw-page-title-main">Hepatic plexus</span>

The hepatic plexus is a sympathetic and parasympathetic nerve plexus that provides innervation to the parenchyma of the liver as well as contributing innervation to some other abdominal structures.

<span class="mw-page-title-main">Esophageal plexus</span>

The esophageal plexus is formed by nerve fibers from two sources, branches of the vagus nerve, and visceral branches of the sympathetic trunk. The esophageal plexus and the cardiac plexus contain the same types of fibers and are both considered thoracic autonomic plexus.

Special visceral afferent fibers (SVA) are afferent fibers that develop in association with the gastrointestinal tract. They carry the special sense of taste (gustation). The cranial nerves containing SVA fibers are the facial nerve (VII), the glossopharyngeal nerve (IX), and the vagus nerve (X). The facial nerve receives taste from the anterior 2/3 of the tongue; the glossopharyngeal from the posterior 1/3, and the vagus nerve from the epiglottis. The sensory processes, using their primary cell bodies from the inferior ganglion, send projections to the medulla, from which they travel in the tractus solitarius, later terminating at the rostral nucleus solitarius.

<span class="mw-page-title-main">Salivatory nuclei</span>

The salivatory nuclei are two parasympathetic general visceral efferent cranial nerve nuclei - the superior salivatory nucleus and the inferior salivatory nucleus - that innervate the salivary glands. Both are located in the pontine tegmentum of the brainstem.

References

  1. ↑ Moore, Keith; Anne Agur (2007). Essential Clinical Anatomy, Third Edition. Lippincott Williams & Wilkins. p. 635. ISBN   978-0-7817-6274-8.
  2. 1 2 Moore, Keith; Anne Agur (2007). Essential Clinical Anatomy, Third Edition. Lippincott Williams & Wilkins. pp. 34–35. ISBN   978-0-7817-6274-8.
  3. ↑ Mehta, Samir et al. Step-Up: A High-Yield, Systems-Based Review for the USMLE Step 1. Baltimore, MD: LWW, 2003.
  4. ↑ Susan, Standring (2016). Gray's anatomy : the anatomical basis of clinical practice. ISBN   9780702052309. OCLC   920806541.
  5. 1 2 Moore, K.L., & Agur, A.M. (2007). Essential Clinical Anatomy: Third Edition. Baltimore: Lippincott Williams & Wilkins. 180. ISBN   978-0-7817-6274-8
  6. 1 2 3 Moore, Keith; Anne Agur (2007). Essential Clinical Anatomy, Third Edition. Lippincott Williams & Wilkins. p. 220. ISBN   978-0-7817-6274-8.
  7. ↑ Lundberg, J. M. (March 1996). "Pharmacology of cotransmission in the autonomic nervous system: integrative aspects on amines, neuropeptides, adenosine triphosphate, amino acids and nitric oxide". Pharmacological Reviews. 48 (1): 113–178. ISSN   0031-6997. PMID   8685245.
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