How are muscles named?

Hey everyone! This is Nicole from Kenhub, and in this tutorial, we'll be discussing how the names of muscles are derived.

So today I wanted to talk a little bit about how the names of muscles are derived as studying anatomy can be quite challenging from remembering the names of muscles to knowing their insertion, origin, innervation and function. And it's sometimes difficult just to remember the name of a muscle, let alone all the other structures that are associated with it.

So in this tutorial we're going to discuss how muscles get their names in order to help make it easier for you to identify muscles and to remember them. And there are quite a few basic conventions when it comes to the naming of a muscle and, once you understand these basic conventions, it becomes much easier to identify them. So in the following slides, we're going to have a look at some basic methods used to name or derive the name of a muscle which usually take into account one or more characteristics of the muscle, and these characteristics include shape, size, orientation of fibers, action, number of origins, origin and insertion, function, and location. And we'll talk a little bit about each of these as we go along.

So let's have a look at the first way we can derive a name for a muscle, and that's from the muscle shape. And if we look at our image over here on the right, of course, we have an image of the deltoid in green here shaped like a triangle. And since the muscle has a fairly well-defined shape, we can assume the triangle might have some significance in the naming, and sure enough, the Greek letter "delta" when written is shaped like a triangle and therefore gives rise to the name deltoid. And so the name for the deltoid muscle arises from its shape. Let's also have a quick look at the trapezius muscle which we can see has a diamond shape and of course you can see that the name of the trapezius is derived from the word trapezoid which refers to the muscle's four-sided shape.

The quality of a muscle with its regard to its dimension can also be used to derive the name of a muscle, and in this case, we're looking at a muscle whose main attribute is its flatness. The French word "plat" means flat and so from that, we get the word platysma for the platysma muscle that covers the superficial aspect of the muscles of the neck. In the case of the serratus anterior muscle, as you can see, the anterior attachments of the muscle are shaped like the fingers of a saw or like the Latin word "serrare" which conveniently means saw hence giving the name serratus anterior.

In many cases, muscles also derive their names from the size of the muscle and some of these terms that we used to denote the size of a muscle include "vastus" which comes from the Latin meaning great – for example, the vastus lateralis muscle – and as you can see on the image on the right, the vastus lateralis muscle is a large muscle that travels all the way down the length of the femur, hence, the name great. The term major is also used to describe how large a muscle is usually in comparison to another muscle – for example, the pectoralis major muscle. And in contrast, the term minor, as you may have guessed, is used to describe a muscle that is the smaller of two similar muscles as is the case with the pectoralis minor muscle.

And the term "maximus" comes from the Latin meaning largest or greatest, and as we can see on the right here, the gluteus maximus muscle is the largest muscle in the pelvic region, hence, the use of the word maximus. The term "minimus" is the Latin for least or smallest and is also used in naming muscles such as the gluteus minimus muscle which is the smallest of the three gluteal muscles or in the case of the hand, the flexor digiti minimi muscle which flexes the little finger.

The length of a muscle can also be taken into account; for example, the word "longus" is used for long muscles such as the longus capitis muscle – a long muscle of the head and neck. The word "brevis" which is the Latin word for short is used to describe short muscles such as the abductor pollicis brevis muscle which is a short muscle of the thumb.

The muscles can also derive their names from the orientation of their muscle fibers. The terms used to describe the orientation of muscle fibers include transverse, oblique and rectus. The term transverse which is used in the naming of the transverse muscle of the tongue is used to describe muscle fibers that run perpendicular to the midline. The term oblique is used to describe muscle fibers that run diagonally at an angle or slanting. A good example of this would be the oblique muscles of the abdomen, and here we can see the external oblique muscle whose fibers as you can see run obliquely. And, finally, the term rectus describes muscle fibers that run parallel to the midline such as in the case of the rectus abdominis muscle which is seen here, and the word "rectus" in Latin means straight and can also be used to describe a muscle than runs straight – for example, the superior rectus muscle which is one of the four rectus muscles that control the movement of the eye.

The fourth quality that is taken into consideration when naming muscles is the action that the muscle facilitates. As such, muscles can be described as flexors, extensors, supinators, pronators, levators, depressors, rotators, adductors, abductors, sphincters, and tensor muscles. These actions are usually the inverse of each other and will point these out as we go along, but it will definitely help to think about these actions mostly in terms of pairs as one counterbalancing the other.

The so-called flexor muscles carry out flexion which is the action of decreasing the angle between two points. And a good example of these muscles are the flexor muscles of the forearm – for example, the flexor carpi radialis which is one of the superficial flexors of the forearm and is responsible for flexing the hand at the wrist joint or radial abduction. Next, extension describes the opposite action of flexion and the extensor muscles are muscles that return the limb to its original position or straighten the limb – for example, the extensor indicis muscle straightens the index finger.

Supination describes the action of turning the limb so that the palm of the hand or the sole of the foot faces upward or outward. For example, when the supinator muscle of the forearm contracts, it rotates the forearm and hand so that the palm faces upwards. Pronation, on the other hand, describes the rotation of the limb so that the palm of the hand or the sole of the foot face downward and inward. For example, the aptly named pronator teres muscle carries out this very action.

The term levator is used to describe muscles that perform a lifting action. For example, the levator anguli oris muscle lifts or elevates the angle of the mouth when we smile. The term depressor is used to describe a muscle that carries out the opposite action of levator muscles which is depression or pulling downward. For example, when we make a sad face, the depressor anguli oris muscle is responsible for pulling the angles of the mouth downward.

Rotators as the name suggests, are muscles that facilitate the rotation of a limb or circular motion about a joint. For example, the muscles of the rotator cuff which although individually do not have the word rotator in their names, are called the rotator cuff muscles simply because this is the action that they collectively carry out. An example of one of these muscles of the rotator cuff is the supraspinatus muscle highlighted here in green, and the supraspinatus facilitates internal and external rotation of the humerus.

Abductor muscles facilitate abduction which is the movement of the limb or appendage away from the midline. The abductor pollicis brevis muscle, for example, abducts the thumb or facilitates the movement of the thumb away from the midline. Adductor muscles, on the other hand, facilitate movement towards the midline as is the case with the adductor pollicis muscles which adduct the thumb as you can see in this image.

The term sphincter is used for muscles that close an opening. For example, the pyloric sphincter muscle. Finally, tensors describe muscles that tighten or make something rigid like the tensor fascia latae muscle which sustains tension of the iliotibial tract.

So now we're going to have a little bit of a look at some muscles which derive their names from the number of points of attachment at the site of origin. And a good example of these muscles are the biceps brachii muscle which has two points of origin, the triceps brachii muscle which has three points of origin, and the quadriceps femoris muscle which has four points of origin. And I'm sure you can see a pattern forming here. The term "bicep" comes from the Latin meaning two-headed, the "bi-" meaning two and the "-ceps" coming from the word caput which means head. Following the same logic, the three-headed muscle is aptly given the prefix "tri-" and the four-headed muscle "quadri-".

In addition to being able to be named after the number of points of origin of a muscle, muscles can also be named according to their point of origin and insertion and one such example is the sternohyoid muscle which is a muscle of the neck region that has its origins on the dorsal surface of the manubrium of the sternum and the sternoclavicular joint and inserts on the body of the hyoid bone.

And, of course, there are also some muscles that have been named according to their function. For example, the Latin word "risus" means laugh and therefore the muscle of facial expression that is used when a person is laughing is called the risorius muscle, and this muscle is sometimes simply referred to as the laughing muscle.

Finally, some muscles are named according to their location in the body. For example, the tibialis anterior muscle is located in front of the tibia. Some muscles also derived their names after their position or location in reference to a similar muscle and in that case the following terms would be used. Infra = inferior meaning below or more caudally situated, supra or superior meaning above or more cranially situated; medialis = medial, middle or medius meaning in the middle or closer to the midline; intermedius meaning intermediate; and lateralis or lateral meaning to the side or away from the midline. An example of a muscle named using one of these basic terminologies would be a muscle we've looked at briefly before, the supraspinatus muscle which is the most superiorly situated of the two spinatus muscles of the scapula.

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