9.2: Muscles of the Upper Arm

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Anatomists refer to the upper arm as just the arm or the brachium. (The lower arm is the forearm or antebrachium.) There are three muscles on the upper arm that are parallel to the long axis of the humerus, the biceps brachii, the brachialis, and the triceps brachii.

The biceps brachii is on the anterior side of the humerus and is the prime mover (agonist) responsible for flexing the forearm. It has two origins (hence the “biceps” part of its name), both of which attach to the scapula bone. It inserts on the radius bone. The biceps brachii has two synergist muscles that assist it in flexing the forearm. Both are found on the anterior side of the arm and forearm. One of these is the brachioradialis muscle which is largely on the forearm (see the next section) and the other is the brachialis, which is largely on the upper arm. The brachialis muscle is deep to the biceps brachii and both its origin and its insertion are more distal to the shoulder than its equivalents on the biceps brachii. Like the biceps brachii the origin of the brachialis is on the humerus. Parts on the brachialis can be seen peeking out from under the biceps brachii, especially lower on the arm. The locations of these three muscles are shown in Figure 9.3.

The anterior view of the deep muscles of the left shoulder — Figure \(\PageIndex{1}\): The muscles of the arm. (CC-BY-4.0, OpenStax, Human Anatomy)

On the posterior side of the arm is the triceps brachii muscle. It the antagonist to the biceps brachii. When the triceps brachii contracts it extends the forearm, undoing any flexing brought about by contractions of the biceps brachii. As a result, when the triceps brachii is contracted, the biceps brachii and its synergists must be relaxed, and vice versa. The triceps brachii has three origins, called the long head, the lateral head, and the medial head. Figure 9.4 shows the three origins of the triceps brachii in different colors. It is easiest to view the triceps brachii from the posterior, but the medial head and its origin are deep to the lateral head and the long head, and so is the medial head of the triceps brachii is partially obscured from the posterior.

Figure \(\PageIndex{2}\):
Figure \(\PageIndex{2}\):. The three heads of the triceps brachii color-coded to distinguish them. Keep in mind, despite the different colors all three are parts of the same one muscle (CC-BY-SA, Wikimedia, BodyParts3D/Anatomography)

LAB 9 EXERCISES 9-2

1. Using the full-scale arm model, locate and identify the biceps brachii, brachialis, and triceps brachii muscles.

2. The following are muscles of arm rotation and adduction. For each, give its origin(s) and insertion(s).

Muscle	Origin(s)	Insertion(s)
Biceps brachii
Brachialis
Triceps brachii

CC LICENSED CONTENT, ORIGINAL

A&P Labs. Authored by: Ross Whitwam. Provided by: Mississippi University for Women. Located at: http://www.muw.edu. License: CC BY-SA: Attribution-ShareAlike

CC LICENSED CONTENT, SPECIFIC ATTRIBUTION

Figure \(\PageIndex{1}\):. The muscles of the arm.. Authored by: OpenStax College. Located at: http://cnx.org/resources/6669b272a691b9377071de429a1336fec0469a5c/1120_Muscles_that_Move_the_Forearm.jpg. Lice nse: CC BY-SA: Attribution-ShareAlike

Figure \(\PageIndex{2}\):. The three heads of the triceps brachii color-coded to distinguish them. Keep in mind, despite the different colors all three are parts of the same one muscle.. Authored by: Was a bee. Provided by: Images in Figure 9.4 were made out of, or made from, content published in a BodyParts3D/Anatomography web site. The content of their website is published under the Creative Commons Attribution 2.1 Japan license. The author and licenser of the contents is http://lifesciencedb.jp/bp3d/?lng=en. Located at: https://commons.wikimedia.org/wiki/F...nimation02.gif. License: CC BY-SA: Attribution- ShareAlike