Relation between "muscles" and "tendons"

[gouttegd]

In Uberon, tendon is textually defined as “dense regular connective tissue that connects muscle to bone”, and is a subclass of connects some 'muscle organ'.

Several individual tendon classes do fit that definition, such as tendon of triceps brachii, which is attached to 'triceps brachii, or calcaneal tendon, which connects some 'muscle of leg'.

However in some cases, the tendon term is said to be part of the associated muscle, e.g.

• tendon of quadriceps femoris, which is part of some 'quadriceps femoris';
• central tendon of diaphragm, which is part of some diaphragm;
• infraspinatus tendon, which is part of some 'infraspinatus muscle' (and also connects some 'infraspinatus muscle').

So should tendons be generally considered to be part of the associated muscles or rather be considered distinct from the muscles and merely attached to them?

(Context: In FBbt we are currently considering introducing proper terms to represent muscles – we only have terms to represent muscle cells at the moment –, and we are not sure yet what to do with the tendons with respect to the muscles. I’d like to be somewhat consistent with what Uberon is doing.)

[cmungall]

Can we have a look at how the pattern varies across ontologies, particularly FMA - we should not be beholden to what has been done but I think this can be informative

[rays22]

The word

1. muscle can mean a type of tissue. Alternatively, the word
2. muscle is used in a broader sense: an anatomical/physiological unit composed of contractile and other tissues, for example tendons. In this sense, an anatomical muscle unit is the result of the subdivision of a complex organ composed of various tissue types.

When muscle is used in the sense of skeletal muscle tissue that is composed primarily of some skeletal muscle fiber than the *tendon(tissue) part of muscle(tissue)` relationship would not be appropriate.

In my opinion it would make more sense to apply the connects some 'muscle organ' pattern to all individual tendons (i.e. anatomical units of tendons resulting from the subdivision of an imaginary tendon organ-system). This would treat tendon units attached to muscles consistently as pieces of tendon tissue.

I hope this helps.

[gouttegd]

Thank you both for your inputs.

In FMA, tendon is defined as an “organ component of muscles”. All tendon classes I have looked at seem to be consistent with that definition, as they are constitutional part of the associated muscles (e.g., distal tendon of deltoid constitutional part of deltoid).

I agree with the double meaning of the word “muscle”. I think this is why in Uberon we have both muscle tissue, which clearly corresponds to the first meaning you mention, and muscle organ, which could correspond to the second meaning. But the way muscle organ is currently defined (“organ consisting of a tissue made up of various elongated cells that are specialised to contract”) does not really fit, as it does not leave room for any other tissue beyond the muscle tissue itself.

[shawntanzk]

@gouttegd assigning this to you, hope you don't mind

[gouttegd]

Follow-up on this.

I dug a bit more on how we represent muscles in Uberon and found another possible problem: how we represent “complex” muscles. That problem could possibly be solved by the same solution as the tendon problem.

We have a very narrow notion of muscle group, which is used for only one muscle: the digastric muscle (digastric muscle group, UBERON:0001562), made of two muscle “bellies” (each belly actually being a muscle in its own right) that are considered together because they both attach to the hyoid bone through a common tendon.

Formally, these notions of “muscle groups” and “muscle bellies” do not seem to be used anywhere else in Uberon.

Informally however (e.g. in text definitions), the notion of “muscle group” does appear elsewhere, as in the quadriceps femoris (UBERON:0001377), which is a group of 4 distinct muscles that are considered together because they all share a common distal tendon that attaches them to the patella.

The way quadriceps femoris is defined conflicts with the way the term is used, however. Textually, quadriceps femoris is defined as “one of the muscles that belong to the group consisting of the rectus femoris and the three heads of the vasts (lateralis, medialis, intermedius)”. That is, the term does not actually refer to the group, but to any of the individual muscles that make up the group (the logical definition matches that textual definition).

But in several places, quadriceps femoris is used as if the term referred to the group, not to the individual muscles. For example, the common tendon of quadriceps femoris (UBERON:0014848) is part_of 'quadriceps femoris' – this can only be correct if quadriceps femoris is understood as referring to the entire group, not to any of the individual muscles. Even worse, each individual muscle (rectus femoris, vastus lateralis, etc.) are also said to be part_of 'quadriceps femoris' – again, this can only be correct if quadriceps femoris refers to the group itself. As a result of this confusion, rectus femoris is both is_a 'quadriceps femoris' (correct only if quadriceps femoris refers to any of the individual muscles of the group) and part_of 'quadriceps femoris' (correct only if quadriceps femoris refers to the entire group).

This kind of problems, combined with the problems of tendons highlighted in the first message of the ticket (some tendons are said to be part_of their corresponding muscles while other are said to be attached_to them) calls for an overhaul of the way we represent muscles, groups of muscles, and their tendons.

I tentatively propose:

• define muscle organ to match with “meaning 2” in Ray’s message above: that is, the muscle organ is the complete anatomical organ, comprising the tendons (so all tendons would be part_of, not attached_to, some muscle organ;
• generalise the notion of “muscle group” that is currently only used for the digastric muscle; that is, create a muscle group term (which could be a subclass of anatomical cluster?) to be used for all “complex” muscles (muscles made of more than one “belly”, such as the digastric or the quadriceps);
• the individual “bellies” that make up a “complex muscle” would themselves be muscle organ, and would be part_of the muscle group;
• muscle group itself would be a subclass of muscle organ; this would allow tendon to also be part of some muscle group, which would cover the case of tendons that are shared by several individual muscles within a muscle group (such as the common tendon of the quadriceps).

See attached figure, which may (or may not…) make my proposal clearer.

[gouttegd]

For the record: the tentative proposal outlined above has been agreed upon in principle in the Uberon call of May 23rd. I’ll implement the proposal and submit PR(s) for definitive approval.

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[emquardokus]

In your example on quadriceps femoris, this is only a muscle group not a single muscle and if any of the individual muscles that create this muscle group are using "is a" then that is not correct from the anatomy side of things. quadriceps femoris is composed of 4 muscles (rectus femoris (RF), vastus medialis (VM), vastus lateralis (VL) and vastus intermedius (VI)) which share a tendon called the quadriceps tendon which is how the muscle group attaches to bone (top of knee cap (patella)). https://en.wikipedia.org/wiki/Quadriceps_tendon#/media/File:Knee_diagram.svg