SNOMED CT Editorial Guide

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The nervous system has two parts, central and peripheral.

  • The central nervous system, sometimes also called the neuraxis, consists of the brain and spinal cord. The pyramidal system is a subdivision of the central nervous system; the extrapyramidal system is part of the brain. 
  • The peripheral nervous system includes all neural structures outside the central nervous system. 

The nervous system is also divided as: autonomic, somatic, and enteric.

  • The autonomic system is further divided as sympathetic and parasympathetic. The autonomic system is not entirely a part of the peripheral nervous system, but the autonomic nerves are peripheral.

Nerve

The word nerve has multiple meanings according to the FMA:

  • nerve trunk
  • neural organ (trunk plus branches, excluding nuclei, ganglia, and roots)
  • neural tree organ, including nuclei, ganglia, roots, etc.

A neural tree organ is defined in FMA as a nonparenchymatous organ which has as its parts an aggregate of neurons (nuclei or ganglia) and their axons which are grouped into fasciculi by connective tissue to form elongated, cable-like structures that are arranged into a tree. A nerve, according to FMA, is defined as a segment of a neural tree organ which has as its parts a nerve trunk and its branches; together with other nerves of the same tree, it constitutes a neural tree. The neural tree structure includes:

  • Cranial nerve
    • Complex cranial nerve-tract
  • Spinal nerve
  • Spinal accessory nerve (strictly neither cranial or spinal nerves)
  • Peripheral nerve
  • Autonomic nerve

Nerve, conventionally has two meanings:

  • An anatomically distinct nerve trunk (without branches) that is identified in a dissection (e.g. the structure that student identifies when a pin is placed in the trunk of the vagus nerve, for instance located on the arch of the aorta)
  • A larger anatomical entity which supports a related set of functions (e.g. all anatomical components of the vagus nerve that are necessary for it to execute its functions (e.g. when a student is asked which nerve is responsible for slowing the heart the answer, the vagus nerve, includes the vagal nucleus, as well as the trunk and branches of the vagus). 
  • Neural tree designates the second concept in order to distingiush it from the first which is only a part (subdivision of) the vagal neural tree.

A third meaning of nerve, defined by the FMA is: Segment of neural tree organ which has as its parts a nerve trunk and its branches; together with other nerves of the same tree it constitutes a neural tree.

For example,

    • Chorda tympani, digastric branch of facial nerve, greater petrosal nerve, posterior cutaneous branch of posterior ramus of cervical nerve, superior lateral cutaneous nerve of arm.
    • If one severs the facial nerve, the meaning refers to the trunk. But if one has facial nerve palsy, the meaning refers to the entire distribution of the nerve and the functions served by it.

Inactivation

There were several concepts with the phrase x nerve and its branches, interpreted as meaning the entire nerve and its branches. Therefore, x nerve and its branches would be a duplicate of entire x nerve, when we interpret entire x nerve as being a neural tree organ.

For example,

    • Entire facial nerve is a neural tree organ, so there is no need for an additional concept called facial nerve and its branches. 
    • Entire cranial nerve is a neural tree organ and structure of cranial nerve is that organ or any part (or branch) thereof. Branches of the cranial and spinal nerves are segments of the neural tree organs from which they branch. 

All concepts named nerve x and its branches were inactivated due to their ambiguity. There are MAY BE A links to structure of nerve x, and entire nerve x. Specifying trunk of a nerve requires a specific concept.

Supratentorial brain

Cerebrum may refer to the supratentorial brain, which is everything except the midbrain, medulla, pons, and cerebellum. In this interpretation, the telencephalon and diencephalon are in the cerebrum. On the other hand, cerebrum may only refer to the parts derived embryologically from the telencephalon, the cerebral hemispheres and the intercerebral commissure (corpus callosum and anterior commissure).

Supratentorial brain may be used for categorizing tumors and for designating the location of swelling that can result in herniation. The telencephalon and diencephalon (including thalamus, geniculate bodies, pineal body, habenulae, and hypothalamus) are definitely supratentorial. The upper part of the midbrain (mesencephalon) is also supratentorial. SNOMED CT excludes all midbrain structures from the supratentorial brain.

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