Tendon function

Image: Your health manager

The tendons, together with the muscles, form the muscular system. This, together with the osteoarticular system, forms the locomotor system, which allows us to move, maintain proper body posture, support other important systems of the human body, etc. Within this entire system, the tendons perform a secondary but fundamental role for the proper functioning of the muscles. In this lesson from a TEACHER we will review what they are and function of tendons in the body. If you want to discover more about this structure, we invite you to continue reading!

Index

1. What are tendons?
2. The transmission of force: main function of the tendons
3. Tendons as energy stores
4. A third function of the tendons: maintaining position

Tendons are bands of connective tissue, more or less thick, very resistant and elastic. This type of dense connective tissue is made up of collagen fibers I (30% of the total mass of the tendon), elastin fibers (only 2% of the total mass) and, fundamentally by

The bundles of collagen fibers, type 1, provide the tendon with resistance to stretching, the elastin fibers for their part it gives tendons their characteristic elasticity while tenocytes are highly specialized connective tissue cells. Surrounding all of them is a kind of broth, called extracellular matrix, composed of substances rich in proteins and sugars (proteoglycans, glycosaminoglycans, glycoproteins and others) that are responsible for nourishing and regenerating collagen fibers, elastin fibers and tenocytes.

Tendons are structures found where they are join muscles and bones. As we will see below, its main function is to join the muscles to the bones, so that the muscles can transfer the movement and the bones, in the places of joint, move on. But this is not the only function of tendons. Tendons, due to their variable composition, but generally rich in collagen, are capable of storing energy.

Image: Slideshare

The best known tendon function is to transmit the force exerted by the muscles, during muscle contraction, to the bones so that they can move. With this, our body can move, breathe, move the limbs and each of our fingers, etc.

This property is due to the union of elastic properties, which provides the elastin and the resistance that is given by the collagen fibers I. The force transmission capacity of each of the tendons will depend, among other things, on the ratio between elastin fibers and collagen fibers and their size. Thus, longer fibers will have greater resistance than short fibers, which will be more elastic as a general rule.

In addition, it depends on the type of joint to which it belongs, the movement in which it intervenes or the muscle length with which it is attached, tendons can have different shapes: narrower, more flattened, more cylindrical, etc. The tendons associated with muscles that make movements called gross, which normally require little delicacy or precision, are usually short and thick.

This is the case of the tendons associated with the glutes or quadriceps. In contrast, tendons associated with muscles that perform fine and precise movements require long and fine tendons; an example is the flexor tendons of the fingers.

The function of tendons as energy transmitters is not the only one. The tendons are also capable of retain that energy to release it later. The energy storage capacity of tendons is given by the collagen fibers.

Collagen fibers are in turn made up of filament-shaped cells called collagen fibrils; collagen fibrils are gathered into collagen fibers by cross-linking. In the case of energy-storing tendons, the links between collagen fibrils are trivalent, that is, each joint is made up of three anchors. This allows the collagen fibrils to slide less over each other, which makes the structure of the whole group (the collagen fiber) is capable of being more resistant to deformations. An example is the Achilles tendon, which supports more than 12 times the body weight when we run and which, when posing the standing on the ground accumulates energy as if it were a spring, to release it when we want to raise the foot.

The components that make up tendons are subjected to many cycles of stretching and contraction and are therefore capable of renew and replenish as they wear out. At a structural level, this means that the tendons responsible for storing energy are specialized in creating structures that are highly resistant to fatigue and continuous stretching and contraction. They do not show as much regeneration or remodeling as the anterior tendons, which must be more elastic and therefore suffer more wear and tear.

Imagine that the tendons are an elastic rubber: the tendons specialized in the transmission of movement would be a more elastic, thin and loose rubber, which does not offer resistance while the tendons tendons responsible for storing energy are those thicker and more resistant elastic rubbers, to which you have to add more force to stretch but which, in return, last longer and tighten more strongly.

Image: Slideplayer

An often overlooked function of tendons is that of maintaining position. In this case, these types of tendons do not intervene in the movement directly, but rather keep the joint components in the correct position, so that they do not shift and dislodge.

An example is the tendons found in the joints of the phalanges of the fingers. These tendons allow our fingers to have mobility, for example, when we type on a computer, without the bones that make up our fingers moving due to movements.

If you want to read more articles similar to Tendon function, we recommend that you enter our category of biology.

• Wavreille, G., & Fontaine, C. (2009). Normal tendon: anatomy and physiology. EMC-Locomotor Apparatus, 42 (1), 1-12.
• Smart Design (March 27, 2018). Tendons are irreducibly complex. Recovered from https://xn--diseointeligente-9tb.org/los-tendones-irreductiblemente-complejos/
• Wikipedia (September 6, 2019). Tendon. Recovered from https://es.wikipedia.org/wiki/Tend%C3%B3n