The 9 arm muscles (classified and explained)

What we commonly refer to as an arm is actually the entire upper limb, made up of the upper arm and forearm being anatomically precise.

The muscles of the arms and forearms allow us to perform everyday actions such as writing, grabbing an object, aiming, holding a weight, and much more. Our upper limbs are capable of performing many movements without which human life would be very different.

Here we will see how they are the muscles of the arm and forearm, all involved in the manual tasks of our daily lives, then we will discover them.

    The muscles of the arm and forearm

    The muscles of the arm and forearm can be classified according to different criteria. In this article we will explain the muscles of the upper limb according to their position, but it is also common to find them differentiated according to whether they are short or long, which allows the muscles to have one movement or another.

    But before we get into the details of what arm muscles are, we must first understand that what we commonly refer to as the arm is not anatomically correct. The arm in the popular sense corresponds to the human upper limb in the anatomical sense, because terminologically speaking correctly the arm is only a part of our upper limbs. So, it can be said that the human upper limbs can be divided into two:

    • Upper arm: region that extends from the collarbone to the elbow.
    • Forearm: region that extends from the elbow to the wrist.

    Within these two anatomical regions, we can differentiate two other parts at the same time:

    Anterior aspect of the arm and forearm

    The anterior aspect of the arm and forearm is the one next to the palm of the hand. To see the front of your upper limbs, simply place your arms across your torso, palms up. By doing this simple exercise, you will see the front side of your arms and forearms.

      Posterior aspect of the arm and forearm

      The back of the arm and forearm is the part next to the back of the hand. To see the back of your limbs, simply place your arms as before only with your palms down.

        Types of arm muscles

        In the arm itself, there are two groups of muscles: the muscles of the anterior face and the muscles of the posterior face.. The muscles of the anterior face are responsible for the flexion movements, while those of the posterior face are responsible for the contraction (muscles in contraction). These muscle groups are called antagonists or antagonists of each other, so when an anterior muscle flexes, the posterior muscle contracts.

        1. Anterior muscles of the arm

        The main anterior muscles of the arm are as follows.

        1. 1. Biceps brachii

        The biceps brachii is a muscle that extends from the collarbone to the elbow, in the intertubercular sulcus of the humerus.. Its main functions are the rotation of the forearm and the flexion of the forearm on the elbow. The biceps brachii is a very large muscle which, when contracted, can be easily seen. It consists of two parts or heads (hence the name biceps): the short part of the biceps and the long part of the biceps.

        1.2. brachial

        This muscle it is at a deeper level than the biceps brachii and is smaller in size. Its shape is wide and flattened. The brachialis is the main forearm flexor muscle on the upper arm.

        1.3. Coracobrachial

        The coracobrachia is a thick prismatic muscle that occupies the space from the scapula to the biceps, passing through the short part of the biceps brachii. This muscle specializes more in rapid movements than in force generation, something that takes care of the biceps, much larger. The main function of the coracobrachia is to raise the arm while keeping the shoulder low, balancing the movement of the arm and restoring the anatomical position.

          2. Posterior muscles of the arm

          As for the muscles of the back of the arm, the two main ones are:

          2.1. triceps brachii

          This muscle occupies most of the posterior region of the arm. As the name suggests, the triceps consists of three portions or heads: a long portion and a vast internal and external. The main function of this movement is the antagonism of the biceps, in this case ensuring the extension of the forearm on the elbow.

          2.2. anconi muscle

          The anconi muscle is small and triangular in shape, and it comes into contact by its proximal end with the triceps and the elbow. It cooperates with the triceps brachii when extending the forearm over the elbow.

            3. Muscles of the forearm

            The muscles we find in the forearm they can be classified into the following three groups.

            • Finger flexors: on the front of the forearm.
            • Finger extensions: on the back of the forearm.
            • Supinators or external rotators of the forearm: at the radial edge, towards the thumb.

            3.1. Forearm muscles

            the list of muscles in the front of the forearm is the next.

            • Round pronator muscle
            • Square pronator muscle
            • Flexor carpi radialis muscle
            • Long palmar muscle
            • Flexor carpi ulnaris muscle
            • Flexor digitorum superficialis muscle
            • Flexor digitorum deep muscle
            • Flexor digitorum longus muscle

            Among these we can highlight the following.

            3.1.1. Flexor digitorum deep muscle

            The deep flexor muscle of the fingers, with the superficial flexor digitorum of the fingers of the hand, it allows to flex the fingers, except the thumb. This muscle is associated with a long tendon that runs down the forearm and crosses the carpal tunnel until it is inserted into the volar aspect of the phalanges of the fingers.

            3.1.2. Flexor digitorum superficialis muscle

            The flexor digitorum superficialis muscle, together with the anterior muscle, is used to flex the fingers, in particular flexion of the middle phalanx on the proximal phalanx and hand on the forearm.

            3.2. Muscles of the back of the forearm

            The list of muscles on the back of the forearm is as follows:

            • Extensor finger muscle
            • Carpus extensor elbow muscle or posterior ulnar muscle
            • Long abductor muscle of the thumb
            • Extensor digitorum brevis muscle
            • Long extensor muscle of the thumb
            • Extensor index muscle
            • Palmar short muscle or palmar cutaneous muscle

            Of all these muscles, most notable is the extensor muscle of the fingers.

            The extensor muscle of the fingers extends over the entire forearm, from the elbow to the dorsal part of the wrist where it is associated with four tendons, passing through them to the fingers two (index), three (middle or heart ), four (ring) and five (small) of the hand, all except the thumb. This muscle is responsible for extending the wrist and the proximal phalanx of the fingers, although it is also slightly involved in extending the arm.

            3.3. Lateral muscles of the forearm

            Finally, it’s time to talk about the lateral muscles of the forearm. Among them we find:

            • Supinator short muscle
            • First radial or long radial
            • Second radial or short radial
            • Supinator longus muscle

            The most notable muscle in this region is the supinator longus..

            It is located at the top of the forearm, near the elbow. This muscle helps rotate the forearm both outward and inward. Depending on the disposition of the elbow, different movements can be performed, which is why it gives a wide variety of movements to the forearm.

            Bibliographical references

            • Moore, KL, Dalley, AF and Agur, AMR (2014). Clinically Oriented Anatomy (7th ed.). Philadelphia, Pennsylvania: Lippincott Williams & Wilkins.
            • Soames, R., Palastanga, N. and Richardson, P., 2012. Human Anatomy and Movement. 6th ed. Elsevier Ltd.
            • Drake, RL, Vogl, AW, Mitchell, AWM, (2014): Grey’s Anatomy for Students (2nd ed.). London: Elsevier Churchill Livingstone.
            • Standring, S. (2016). Grey’s Anatomy (41ª ed.). Edinburgh: Elsevier Churchill Livingstone.

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