About Tendons and Ligaments

By Thomas Griner with Tamsin Lee

For a long time it was thought that a tendon and the fascia of its corresponding muscle were all one continuous piece, because both are fibroblastic tendon cells, and because each fascicle in the muscle belly is identical to the fascicles in the corresponding tendon.  With the advent of the electron microscope however, we were able to see that muscle endomysium is a separate entity with its own desmosome; i.e. the connective tissue, or fascia that wraps the muscle is not the identical tissue as the tendon issuing from the muscle, even though they are the same type cells.

The Golgi tendon organ attaches to the tendon just at this point of union between the muscle and tendon. The GTO is actually attached to what has been, in the muscle, the endomysium surrounding the individual cell (except, as stated above, at that point the endomysium has run out and the tendon begun).  However, the distinction of the endomysial layers around the muscle fibers, and the perimysial layers around the fascicles (which is not attached to the muscles, but forms a sheath around them), continues in the tendon. Therefore, tendons have the same logistical separation into fascicles as do muscles, for the same logistical reasons. Many book illustrations do not depict the endomysium – they show nothing around each of the individual muscle fibers, nor do they show the desmosomes separating muscle from tendon.  Instead most show the tendon attaching directly to the muscle fibers, which is not possible.

It is usually said that the while the muscle spindle is in parallel with the muscle, the Golgi organ is in series with it; actually, both the spindle and Golgi organ are in parallel.  The muscle spindle is attached to the side of the perimysium, whereas the Golgi organ is attached to the side of the endomysial layer of the tendon. Therefore, the Golgi organ is actually in parallel with the tendon that happens to be in series with the muscle.  Incidentally, “in parallel’ and ‘in series’ are anatomical designations, rather than neurological.

It is the tendon which is struck when checking tendon reflexes. And striking a tendon reflex point – knee, elbow, ankle – does not activate a Golgi tendon organ. It is often mistakenly thought that the term “tendon reflex” refers to activating the Golgi tendon organ, but Golgi organs actually inhibit rather than cause muscle contraction; it is the muscle spindle bag fibers which cause muscle contraction through the myotatic stretch reflex.

In the case of the knee tendon reflex, the Golgi organ is located above the knee, in the deflective portion at the end of the muscle belly; striking there would produce only a local action from the deflection of the giving fibers of the muscle. But striking just under the patella is striking the less deflective tendon, which activates the entire muscle. And because we know that Golgi organs inhibit contraction, an erroneous assumption exists in some camps that grinding away on the Golgis will relax muscle in spasm. But in fact, one cannot gnarl the Golgis without activating the muscle spindles (stretch reflex). 

Because ligaments and tendons are both connective tissue made from collagen fiber bundles, they are usually grouped together and thought of as closer relatives than tendons and muscles. But the muscle belly is not the total muscle; its tendons are a part of the muscle. In fact, the tendon is called the “stroma”, or supporting framework, and the muscle belly is called the “parenchyma”, or functional tissue of an organ as distinguished from its connective or supporting tissue. Together the stroma and the parenchyma make up the “muscle-tendon unit”.

There are two main differences between tendons and ligaments. The first difference is that while both ligaments and tendons have bundles of parallel collagen fibers (collagen fibers are inherently elastic because they are parallel fibers of helical crystals, which look like a coiled spring), the fibers in ligaments are arranged in criss-crossed layers, whereas the tendon’s fibers remain in strictly parallel strands.

Ligaments are composed mainly of bundles of white fibrous tissue closely interlaced with one another, and present a white, shining, silvery aspect. Although ligaments are pliant and flexible, so as to allow freedom of movement, they are nevertheless strong, tough, and not able to extend. They are not involved in stretching, and even though their main job is to keep the joints together, ligaments do not become involved in maintaining the integrity of movable joints unless the muscles are breached. Elasticity is not a desirable quality in ligaments because they act as backup to the muscle-tendon unit; therefore, their inherent collagen elasticity is neutralized by the criss-crossed layers of their fibers.  However, white elastin between each layer of the ligament allows some movement between the layers for flexibility, change of motion, or direction; otherwise it would be an almost rigid structure. 

However, there are four examples of truly elastic ligaments in the human body, which are:

1. Ligamentum flavum, made from yellow elastic fibers rather than white elastic fibers, coloring the ligament yellow. It runs through the entire spinal column, all the way from top to bottom. Because its job is to protect the spinal cord from the spinal column, it doesn’t hold anything in place or to stop any joints from dislocating, but is rather a soft, elastic curtain which gives with all the movements of the spinal column.

2. Broad ligament of the uterus holds the uterus in place, and of course has to stretch when the uterus expands, which is why it’s elastic.

3.  The vocal chords.  We have two sets of vocal chords: vocal ligaments and vocal muscles. We get falsetto by relaxing the muscles so that nothing but the ligament is vibrating.

4. The suspensory ligaments in the lens of the eye.  They have to be elastic, because when the eye muscles want to change the diameter of the lens, the ligaments have to stretch. 

Tendon fiber bundles, on the other hand, are parallel and twisting rather than criss-crossed and overlapped, which allows them much more movement than ligaments. The reason the tendon is twisting, by the way, is because each one of its collagen fibers is twisting; so when these fibers are combined, the tendon tends to twist, just like the DNA helix. When DNA molecules are put together, one twists the next, and that in turn twists the next one.  In the same way, the inherent twisting of the collagen fiber creates the twisting in the tendon.

The second difference between tendons and ligaments is that while ligaments are totally passive structure, tendons, including retinaculae, are active structure.  This is because the tendon’s helical crystals are piezoelectric.  

Piezoelectricity has to do with electricity or electric polarity produced in certain non-conducting crystals when subjected to pressure or strain; piezoelectricity turns rapidly pulsing electrical currents into rapidly pulsing mechanical action, as in an ultrasound unit.  Piezoelectric crystals expand and contract when injected with electricity, and they also generate electricity when mechanically distorted.  The muscle therapist is mainly interested in the fact that when electricity (innervation) is introduced into the piezoelectric helical coil spring of the collagen tendon fiber, it tenses, or stiffens (rather than contracts).

Where does that electricity/innervation come from? The motor nerves that innervate muscle fibers give off co-laterals (little parallel sidetrack nerves), some of which go to the muscle spindles and some to tendons of the muscles they’re innervating.  Tendons must stiffen at the same time the muscles contract, or they would stretch out and counteract the contracting action of the muscle belly. There would be no shortening of the muscle tendon unit. So again, tendons are active, while ligaments are passive.

Some articles state that tendons, when over-stretched, “undergo permanent elongation and loss of elasticity”. If this were true, we would become permanently disjointed.  What really happens is the muscle becomes hypertonic because more and more fibers are contracting continually, which creates added stress on the tendons, which then become extra-fibrotic.

Remember, each collagen fiber is a coiled spring; say there are four coiled springs which are operating very well within their limits of stretch under a certain stress; but if more stress were added, it would overstretch the springs until additional coils were also added. The tendons have the ability to call for more springs, (because the extra piezoelectric voltage given off stimulates the fibroblasts to produce more fibers), thus spreading the stress of the permanently contracting (hypertonic) muscle over a larger number of coils, until the tendons are back within the range of their allowed limits.  But now it is harder to move and stretch the tendon.  That extra fibrosity is the only real loss of movement; although still elastic, it takes more force to make it happen. For that reason, when muscle tone increases, the stretch reflex decreases; the muscle no longer needs to resist force – protect itself through dynamic contraction – as much because it can’t stretch as much to begin with.

However, even when one’s tendons are fibrotic, the stretch reflex mechanism is activated in repeated or intense stretching, driving the muscle crazy. And even someone with an extremely shortened muscle belly can temporarily extend the tendon, which is why ballet theaters have a barre in the back of the stage; as dancers dance and use their muscles, the co-lateral nerves running to their tendons tell the tendons to stiffen. Once offstage, the dancers stretch out their tendons at the barre, but as soon as they dance again, the tendons shorten up. This stretching/stiffening of the tendons does nothing except possibly thicken them with more coils.  But a dancer’s shortened muscle bellies, which have lost their range of motion, are also stretched at the barre, driving them into more contraction (hypertonic spasm). That’s why the derrières of ballet dancers tend to bulge out – the gluteal muscles are incredibly spastic.

Muscle fibers twitch on and off in a fraction of a second, but tendons, once stiffened, take longer to let go; because of this and the fact that they don’t provide much movement, tendons cannot be used in place of muscles.   

This article was found in http://www.tendonitis.net  and is provided to you on this webpage by John Chow, a registered practitioner of Chinese medicine, acupuncturist, masseur, healer, teacher of Tai Chi, Chi Kung, martial arts and spiritual path.     Contact:  Vajra_master@yahoo.com http://www.yellowbamboohk.com