Muscle classification

The one described in the previous article is a simple example, but many muscles in the human body have a much more complex structure.

The biceps and triceps muscles, for example, have respectively two and three heads of origin, to which correspond as many bellies and as many tendon origins. For both, on the other hand, the insertion is unique (the flexor and the common extensor of the fingers, on the other hand, have several insertion heads and a single head of origin).

In general, the muscles provided with several heads, in addition to having a "single insertion, are innervated by branches of the same nerve; all this allows a better muscular efficacy, resulting on the one hand in a finer control of the movement and on the other" in a greater development of strength.

Other muscles, with their terminal head, on the other hand, have multiple insertions; in this we speak of bicaudate, tricaudate and quadricaudate muscles.

Based on the number of POINTS OF ORIGIN, muscles are classified into:

monociceps muscles: they are those that have only one point of origin
biceps muscles: are those that have two points of origin
triceps muscles: they are those that have three points of origin
quadriceps muscles: they are those that have four points of origin

Based on the number of INSERTION POINTS, muscles are classified into:

monocaudate muscles: they are those that have only one point of insertion.
bicaudate muscles: these are those that have two insertion points.
tricaudate muscles: these are those that have three insertion points.
pluricaudate muscles: they are those that have more insertion points.

It being understood that most of the muscles are fixed on two movable bones, there are also muscles in which one or both points of attachment are inserted on fixed bones, or on the skin or mucous membranes. The mimic or furry muscles, for example, are insert with at least one end into the dermis (middle layer of the skin).

Based on their POINT OF ORIGIN and POINT OF INSERTION, muscles are classified into:

Skeletal muscles: they are those that have both origin and insertion in the bones.
Furry muscles: they are those that have at least one of the attachment points in the dermis; their contraction moves the skin.

The morphology of the muscles allows them to be distinguished into four main categories:

LONG or FUSIFORMS MUSCLES: they are very developed in length and generally have a very voluminous fleshy mass (called muscular belly) that narrows in the periphery; in many cases it is possible to notice several muscular bellies (biceps, triceps, quadriceps), with multiple origin and single distal tendon insertion.
The long muscles are endowed with a remarkable shortening and elongation capacity (they are strong muscles, but they tire easily); they are mainly present in the limbs and allow the execution of large movements.
WIDE MUSCLES: they are developed in width; consequently they generally have a broad and flattened belly. They have little capacity for lengthening and shortening, generally covering important areas of the body. They form the wall of the abdomen, thorax and pelvis (rectus abdominis, great dorsal); they are power muscles (they allow prolonged efforts, but with less effective), containment and hedging.
The large muscles are inserted into the skeleton through aponeurosis, a sort of enlarged tendons made up of robust connective fibers.
SHORT MUSCLES: length, width and thickness are almost the same, but the shape can be very different; they are located around the joints or the spine. They have a stabilizing and synergistic function with other muscles.
ANULAR or CURVILINEAL MUSCLES: their muscle fibers, which form a ring capable of narrowing the opening they delimit, surround the natural orifices of the body. the other skeletal muscles) and in sphincter muscles (they have a muscle tone so accentuated that they remain in a continuous state of contraction; this state can be modified by a reflex mechanism or by the effect of the will: the anal sphincter muscles are an example).

According to the SHAPE, the muscles are classified into:

long muscles: those in which length prevails over width and thickness
large muscles: they are those in which the thickness is clearly less than the length and width
short muscles: are those in which the length, width and thickness are almost equal
annular muscles: are those that surround the natural orifices of the body
- orbicular: they are those that, due to their characteristics, behave like other skeletal muscles;
- sphincters: they are those that due to their characteristics behave in a particular way, with an accentuated muscle tone and in continuous contraction.

When the muscles are formed by two bellies like the biceps, but joined by an "intermediate common tendon insertion, we speak of digastric muscles (gastèr in Greek it means, precisely, belly). An example is the digastric of the neck, which is part of the muscles that move the lower jaw down to the hyoid bone.

Based on the PRESENCE OR LESS OF INTERMEDIATE TENDONS, the muscles are classified into: