Posted on 09 Nov 2011 17:18
By Ground Up Strength
The various scientific names of the body's 600 to 650 or so muscles,1 at first, appear to be a bewildering hodgepodge of Greek and Latin. You may think that anatomists were just picking mysterious words out of an ancient hat in order to confuse you. That is not true at all, however. Although in some cases the methods used to name muscles are not very effective, the names of muscles are based on a naming system and, believe it or not, there is order and logic in how the muscles are identified. The more you are exposed to the study of skeletal muscles, the more you will begin to recognize the underlying structure. Often, knowing the meaning of the words will help you understand what muscle is being referred to just by its name. Sometimes, though, even knowing the meanings of the words will not help and all you can do is memorize them.
Still, being familiar with the meanings and the underlying system of naming is better than relying on rote memorization alone, because even though you won't always be able to find a muscle by its name, you will at least know what muscles are NOT being referred to. Knowing the structure of muscle naming can also help you decipher the function, location, and other information about muscles form their names alone.
There are several primary muscle characteristics that are used to choose a name, but remember that not all of these characteristics will necessarily be used. Understanding this system will not guarantee that you will be able to recognize the location or function of a muscle by its name alone, unfortunately. For instance, you would not be able to predict that the vastus lateralis is a quadriceps muscle. However, you would know that it is quite a large muscle and it is located "on the side."
Muscles May Be Named According to Any of These Characteristics
1. What is the size of the muscle? Its it bigger than a muscle near it, or smaller?
2. Where is the muscle located? This may refer to a body part, or to the origin and insertion of a muscle.
3. What is its basic shape? What does it look like?
4. What is its function? Does it extend a joint or flex it?
5. How many origins does it have ("heads", parts or divisions)?
6. What is the muscle's origin and insertion?
7. What is the muscle orientation relative to the midline of the body? Or, in other words, in what direction do the muscle's fibers run? Are they straight (rectus), or perhaps oblique (slanted)?
Each of these basic characteristics are "coded" with root words used to form the larger name. Many times, as well, a muscles name must be based on its relationship to another similar or paired muscle. Let's look at some of the basic words used to describe muscles:
Words That Refer to Muscle Size
- Maximus: largest (gluteus maximus is the largest muscle of the buttock)
- Minimus: smallest (gluteus minimus is the smallest muscle of the buttock)
- Medius: intermediate in size, do not confuse with medialis (gluteus medius is the the intermediate sized muscle of the three buttock muscles)
- Major: larger (pectoralis major is the larger muscle of the chest)
- Minor: smaller (pectoralis minor is the smaller muscle of the chest)
- Brevis: shortest (peroneus or fibularis brevis is the shortest of the peroneal muscles)
- Longus: longest (peroneus or fibularis longus is the longest of the peroneal muscles)
- Vastus: great or huge (used for two muscles of the thigh: vastus lateralis and medialis)
Words that Refer to Muscle Shape
- Deltoid: triangular (e.g. deltoid muscle of the shoulder)
- Rhomboid: diamond shaped (e.g. rhomboideus minor and major muscles, collectively the "rhomboids")
- Quadratus: square or four-sided (e.g. quadratus lumborum or quadratus femoris)
- Trapezius: trapazoidal shaped (e.g. trapezius muscle)
- Serratus: serrated or saw-toothed (e.g. seratus anterior)
- Teres: round or cylindrical shaped (e.g. pronator teres)
- Platysma: flat (e.g. platysma muscle of neck)
Words that Refer to Body Parts or Regions (Location)
- Pectoral: chest (two muscles, pectoralis major and minor)
- Brachii: arm (biceps brachii)
- Carpus: wrist (flexor carpi radialis and ulnaris)
- Palmaris: palm of the hand (e.g. palmaris longus)
- Digiti: finger or toe, singular (extensor digiti minimi)
- Digitorum (finger or toes, plural (flexor digitorum profundus)
- Indicis: index finger (extensor indicis)
- Hallucis: great or big toe (abductor hallucis)
- Femoris: thigh (rectus femoris)
- Gluteus: gluteal or buttock region (three muscles, gluteus maximum, minimum, and medius)
- Tibialis: lower leg or shin bone (tibia) (tibialis anterior and posterior)
- Peroneus: fibula, sometimes fibularis is used (peroneus longus)
- Spina, Spinalis: spine (erector spinae, spinalis cervicis and capitis)
- Spinatus: spine of the scapula (infraspinatus and supraspinatus)
- Pollicis: thumb (adductor and opponens pollicis)
- Oculi: eye (orbicularis oculi)
- Oris: mouth (depressor anguli oris)
- Labii: Lips (levator labii superioris)
- Capitis: head (splenius capitis)
- Cervicis: neck (semispinalis cervicis)
- Thoracis: thorax (spinalis thoracis)
- Abdominis: abdomen (rectus abdominus)
- Lumborum: lower back or lumbar (quadratus lumborum)
- Scapularis: scapula or shoulder blade (e.g. levator scapulae)
- Costals: ribs (intercostals or internal intercostal muscles meaning "muscles between the ribs")
Words that Refer To Relative Location
- Lateralis: located to the side or laterally (vastus lateralis)
- Medialis: located toward the middle or midline (vastus medialis)
- Anterior: toward the front or anterior surface (tibialis anterior or serratus anterior)
- Posterior: toward the rear or posterior surface (tibialis posterior)
- Superior or Superficialis: superficial or toward the surface (flexor digitorum superficialis and obliquus capitis superior)
- Inferior: underneath or away from the surface (Obliquus capitis inferior)
- Profundus: located deep (flexor digitorum profundus)
- Supra: above or over (supraspinatus)
- Infra: below or beneath (infraspinatus)
- Sub: below or under (subscapularis)
- Internal: inner (internal oblique)
- Inter: between (intercostals)
- Dorsi: of the back (latissimus dorsi)
Words that Refer to Muscle Fiber Direction
Note that some writers confound fiber direction terms with shape terms, so that rectus, which refers to fibers that run up and down, straight and parallel with the midline, are called "straight" muscles in terms of shape. However, fiber direction does not necessarily denote the overall profile of a muscle, only the orientation of the fibers.
- Rectus: straight, or "erect", specifically meaning parallel to the midline (rectus femoris meaning "straight muscle of the thigh")
- Transversus: transverse or perpendicular to the midline (transversus abdominis or transverse abdominis)
- Oblique: slanted or diagonal to the midline (external oblique)
- Orbicularis, Sphincter: a name given to ringlike muscles that encircle and orifice and that may form a constricting passage (lower esophageal sphincter and orbicularis oris and anal sphincter)
Words that Refer to Number of Origins or Heads
The suffix "-ceps" means heads. A head is a major division of a muscle that has its own tendon.
- Biceps: two heads (biceps brachii which means "two headed muscle of arm" and biceps femoris which means "two headed muscle of the thigh")
- Triceps three heads (triceps brachii which means "three headed muscle of arm")
- Quadriceps: four heads (quadriceps femoris which means "four headed muscle of the thigh", commonly called the quadriceps). Technically the "quadriceps" are different muscles, however, not one muscle with multiple origins.
Words that Refer to Actions
Since the various muscle joint actions are so common, muscles that use action terms in their names usually also give other clues as to their appearance or location.
- Flexor: flexes joint, or brings two ends closer together, decreases joint angle (flexor carpi radialus)
- Extensor: extends joint or bring two ends further apart, increase joint angle (extensor carpi radialus)2
- Levator: elevates a structure or part (levator scapulae)
- Depressor: depresses a structure or part (depressor anguli oris)
- Adductor: adducts or moves a part toward the midline
- Abductor: abducts or moves a part away from the midline3
- Pronator: pronates or turns the hand or forearm downward or backward (pronator quadratus and pronator teres muscle)
- Supinator: supinates or turns the hand or forearm upward or forward (supinator muscle)4
- Rotator: rotates one structure relative to another (rotatores spinae)
- Opponens: Refers to thumb actions only and named for the action of opposition, which is when the tip of the thumb is brought into contact with other fingers (opponens pollicis)
Some special action words used for certain muscles:
- Sartorius Muscle: Derived from the muscles activity when crossing the legs and named after the Latin word for tailer, sartor. Tailors used to sit on the floor cross-legged to do their work, before sewing machines were invented. Other explanations are also put forth, such as the cross-legged pedaling action of old sewing machines, which enlarged the muscle in tailors, and the muscles location along the "inseam."
- Buccinator: Derived from the muscles action in compressing the cheeks, which occurs when pursing the lips and blowing forcefully, as when playing the trumpet. The word buccinator means "trumpet player" so the buccinator is the "trumpet player muscle."
- Risorius: Derived from this facial muscle's action in producing the facial expression associated with laughter, which is risor in Latin. The actual expression of the muscle is more appropriately described as a grimace. 2
- Masseter: Derived from the muscles major action in chewing, coming from the Greek masētēr, meaning "a chewer."
Words that Refer to Origins and Insertions
It is not necessary to name every possible origin and insertion for each muscle. Only a relatively few muscles are named by these terms. Below are some examples, giving the muscle name and the words for the individual attachments that form the name. The first part of the name always refers to the origin and the second part to the insertion, which are joined together to form a compound word.
- Sternocleidomastoid: Sterno and cleido for its origin, the sternum and clavicle; and mastoid for its insertion, the mastoid process.
- Brachioradialis: Brachio for its origin on the upper arm and radialis for its insertion on the radius of the forearm.
- Genioglossus: Genio for its origin on the chin or "geneion" and glossus for its insertion on the tongue (glossus).
- Sternohyoid: Sterno for its origin on the sternum and hyoid for its insertion at the hyoid bone.
- Coracobrachialis: Coraco for its origin on the corocoid process of the scapula and brachialis for its insertion on the humerus of the upper arm.
As can be seen by the various terms and methods used to name muscles, it is by far a perfect system. Unfortunately, throughout the many years spent describing and naming the body's muscles, anatomists failed to stick to one method. Although there is indeed structure, some parts of the structure is more scientific than others. For instance, there is nothing particularly scientific in calling a muscle "deltoid" because it is shaped like a triangle. Likewise, although a word like "femoris" would seem very precise, there are many muscles associated with the femoris, or "thigh bone" and therefore a name like "quadratus femoris" means only "a square-shaped muscle of the thigh bone," which still requires us to memorize the muscle rather than to be able to guess its precise location and function by its name. This muscle, after all, could be located on the anterior or the posterior part of the thigh and could be a hip muscle or a knee muscle. Although gluteus maximus sounds sufficiently scientific to most laypeople, calling a muscle "a large buttock muscle" is hardly scientific.
It would seem, then, that those names giving location and action are best, and these would be termed physiological names. Well, for those studying only human anatomy and human muscles, this may be the case, but for comparative anatomy and to describe the same muscles in different animals, it is a mess, as not all muscles necessarily share the same exact function in all animals. As stated above, perhaps the best system is a morphological one, which uses the origin and insertion of a muscle for its name, at least for purposes of comparative anatomy. Still, for students of human kinesiology and physical training, comparative anatomy is, at best, a side-line. Therefore, more descriptive names are more useful and most of us should be thankful that the morphological system never really caught on, although anatomists may grapple with the incongruities.
There will always be some memorization involved in learning the names, functions, and locations of the muscles. There is just no way around it. Yes, you may know that the brachialis has something to do with the arm, because of the "brachi" in the word, but that's all you know. How is it different than the brachioradialis or the coracobrachialis?
After studying the terms above, you should start to see patterns emerging. As you move down the lists, you should start to recognize the terms previously encountered in the muscle examples given, so that, as you learn, the names start to make more and more sense. This is especially the case in the more descriptive names. Fortunately, the other, badly named muscles, such as the deltoid and trapezius muscles, are the more familiar muscles to laypeople, and most shouldn't have much trouble with these bad apples. Learn all the terms in this article, and even with no memorization of the individual muscles you will know a great deal more than most people about the muscles of your body.
Clearing Up Some Anatomical Confusion
As you read this article and study the lists, you may wonder about the terms arm, forearm, leg, and thigh. How are you supposed to know what arm means? Does it mean my upper arm or my lower arm (forearm)?
When it comes to anatomy, we rely on certain foregone assumptions. That is, anatomists rely on these assumptions while everyone else is confused by them. When this article refers to the "arm" as in "brachii" it means the upper part of the arm. Why? Because in anatomical terms arm means upper arm and forearm means lower arm. For the legs, it's the opposite. The word leg, in anatomical terms, means the lower leg and the word thigh means the upper leg. So your arm is actually only the portion of that appendage from your elbow to your shoulder and your leg is only the part of that appendage from your knee down.
Example of Specific Muscles and How They Were Named
The following is a list of specific muscle name explanations, with images, that should assist you in your study. When possible, further explanation to the relevant anatomy is given. These muscles are listed in no particular order, they are just examples!
The infraspinatus is named for its position relative to the spine of the scapula. "Spinatus" refers to the scapular spine and "infra" means that the muscle is situated below it.
The image above has the spine of the scapula labeled. I have also labeled the suprapinatus fossa, for reference. The scapular spine separates the infraspinatus and supraspinatus fossa on the posterior surface of the scapula. Note that the scapular spine ends on the acromion process, where the clavicle joins, forming the acromioclavicular joint. See that the muscles is situated "below" the spine.
Extensor Carpi Ulnaris
The extensor carpi ulnaris, as you should immediately know if you've been paying attention, is an extensor of the wrist (carpus).
The muscle inserts onto the ulna bone of the forearm. However, the name is not simply an indication of where the muscle inserts. It actually inserts onto the base of the fifth metacarpal (proximal part of the little finger). Instead, the "ulnaris" in the name describes its relationship to the bone and its role in movement. Here, we have an extensor of the wrist on the ulnar side which means it is an ulnar extensor of the wrist. Without opposition from other flexors and extensors on the radius, the extensor carpi ulnaris, together with the flexor carpi unlaris, would tend to cause wrist adduction or "ulnar flexion" rather than pure wrist extension. As it is, the muscle is active in both wrist extension and wrist adduction.
This muscle arises from the coracoid process of the scapula, hence, coroco- refers to this origin. As you may note above, the term brachii refers to the upper arm or humerus bone and this muscle inserts onto the humerus, in the middle of the medial border of the shaft. This can be thought of as a muscle of the upper arm that arises from the coracoid process, and its major actions are shoulder (arm) adduction and flexion.
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