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Deltoid muscle is the muscle forming the rounded contour of the shoulder. It was previously called the Deltoideus and the name is still used by some anatomists. It is called so because it is in the shape of the Greek letter Delta (triangle). The deltoid is a frequent site to administer intra-muscular injections. |
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Biceps (biceps brachii)
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In human anatomy, the biceps brachii is a muscle located on the upper arm. The biceps has several functions, the most important simply being to flex the elbow and to rotate the forearm. The biceps brachii is arguably the best known muscle, as it lies fairly superficially, and is often well-defined even in non-athletes. The muscle is popular amongst bodybuilders, and can grow quite large through weight training.
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Abs (rectus abdominis)
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The rectus abdominis muscle (commonly known as "abs") is a paired muscle running vertically on each side of the anterior wall of the human abdomen (and in some other animals). There are two parallel muscles, separated by a band of connective tissue called the linea alba (white line). It extends from the pubic symphysis/pubic crest inferiorly to the xiphisternum/xiphoid process and lower costal cartilages (5-7) superiorly. It is contained in the Rectus sheath. The rectus is crossed by three fibrous bands called the tendinous inscriptions. Colloqiual names for the appearance of a well-defined rectus abdominis include a "six pack" and "washboard abs".
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Triceps (triceps brachii)
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Triceps brachii muscle is often simply called the triceps (both singular and plural). However, the term triceps (Latin for "three-headed") can mean any skeletal muscle having three origins, such as the triceps surae. The three heads have the following names and origins: - The "Long head": infraglenoid tubercle of the scapula
- The "Lateral head": posterior shaft of the humerus, lateral and superior to the radial (spiral) groove.
- The "Medial head": posterior shaft of the humerus, medial and inferior to the radial (spiral) groove.
The fibers converge to a single tendon to insert onto the olecranon process of the ulna (though some research indicates that there may be more than one tendon.) Many mammals have a fourth head, the "Accessory head", which is between the Lateral and Medial heads.
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Chest (pectoralis)
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Chest (pectoralis) is the region of the body between the neck and the abdomen, along with its internal organs and other contents. It is mostly protected and supported by the ribcage, spine, and shoulder girdle. Contents of the chest include the following: - organs
- muscles
- major and minor pectoral muscles
- trapezius muscles and neck
| | Pectoralis major | | | Musculus pectoralis major |
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Traps (upper trapezius)
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In human anatomy, the trapezius is a large superficial muscle on a person's back. It is innervated by the accessory nerve (Cranial Nerve 11) and the ventral rami of cervical vertebrae 3 and 4, which also supplies the sternocleidomastoid muscle. The two Trapezius muscles together resemble a trapezium, or diamond-shaped quadrangle: two angles corresponding to the shoulders; a third to the occipital protuberance; and the fourth to the spinous process of the twelfth thoracic vertebra  Superficial dissection of
the right side of the neck, showing the carotid and subclavian arteries. |  The arteries of the face and scalp. |
Because the fibers run in different directions, it has a variety of actions, including: - scapular abduction (shrugging up or lifting the shoulders)
- scapular retraction (drawing the shoulder blades toward the midline)
- scapular depression (pulling the shoulder blades down)
Different fibers control different actions: - The superior (upper) fibers elevate the scapula
- the middle fibers retract it
- The inferior (lower) fibers depress it
- When the superior and inferior fibers act together, they superiorly (upwardly) rotate the scapula
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