出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2016/05/24 03:40:24」(JST)
| Deltoid muscle | |
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Deltoid muscle
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Muscles connecting the upper extremity to the vertebral column
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| Details | |
| Origin | the anterior border and upper surface of the lateral third of the clavicle, acromion, spine of the scapula |
| Insertion | deltoid tuberosity of humerus |
| Artery | thoracoacromial artery, anterior and posterior humeral circumflex artery |
| Nerve | Axillary nerve |
| Actions | shoulder abduction, flexion and extension |
| Antagonist | Latissimus dorsi |
| Identifiers | |
| Latin | musculus deltoideus |
| Dorlands /Elsevier |
m_22/12548745 |
| TA | A04.6.02.002 |
| FMA | 32521 |
| Anatomical terms of muscle
[edit on Wikidata]
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In human anatomy, the deltoid muscle is the muscle forming the rounded contour of the shoulder. Anatomically, it appears to be made up of three distinct sets of fibers though electromyography suggests that it consists of at least seven groups that can be independently coordinated by the nervous system.[1]
It was previously called the deltoideus (plural deltoidei) and the name is still used by some anatomists. It is called so because it is in the shape of the Greek capital letter delta (Δ). It is also known as the common shoulder muscle, particularly in other animals such as the domestic cat. Deltoid is also further shortened in slang as "delt".
A study of 30 shoulders revealed an average mass of 191.9 grams (6.77 oz) (range 84 grams (3.0 oz)–366 grams (12.9 oz)) in humans.[2]
The deltoid originates in three distinct sets of fibers, often referred to as "heads":[3]
Fick[14] divided these three groups of fibers, often referred to as parts (Latin: pars) or bands, into seven functional components:[15] the anterior part has two components (I and II); the lateral one (III); and the posterior four (IV, V, VI, and VII) components. In standard anatomical position (with the upper limb hanging alongside the body), the central components (II, III, and IV) lie lateral to the axis of abduction and therefore contribute to abduction from the start of the movement while the other components (I, V, VI, and VII) then act as adductors. During abduction most of these latter components (except VI and VII which always act as adductors) are displaced laterally and progressively start to abduct.[15]
From this extensive origin the fibers converge toward their insertion on the deltoid tuberosity on the middle of the lateral aspect of the shaft of the humerus; the middle fibers passing vertically, the anterior obliquely backward and laterally, and the posterior obliquely forward and laterally.
Though traditionally described as a single insertion, the deltoid insertion is divided into two or three discernible areas corresponding to the muscle's three areas of origin. The insertion is an arch-like structure with strong anterior and posterior fascial connections flanking an intervening tissue bridge. It additionally give off extensions to the deep brachial fascia. Furthermore, the deltoid fascia contributes to the brachial fascia and is connected to the medial and lateral intermuscular septa. [16]
The deltoid is supplied by the posterior circumflex humeral artery and the deltoid branch of the thoracoacromial artery which branches from the axillary artery.[17]
The deltoid is innervated by the axillary nerve.[17] The axillary nerve originates from the anterior rami of the cervical nerves C5 and C6, via the superior trunk, posterior division of the superior trunk, and the posterior cord of the brachial plexus.[citation needed]
The axillary nerve is sometimes damaged during operations on the axilla, such as for breast cancer. It may also be injured by anterior dislocation of the head of the humerus.[citation needed]
When all its fibers contract simultaneously, the deltoid is the prime mover of arm abduction along the frontal plane. The arm must be medially rotated for the deltoid to have maximum effect{[18]}. This makes the deltoid an antagonist muscle of the pectoralis major and latissimus dorsi during arm adduction.
The anterior fibers are involved in shoulder abduction when the shoulder is externally rotated. The anterior deltoid is weak in strict transverse flexion but assists the pectoralis major during shoulder transverse flexion / shoulder flexion (elbow slightly inferior to shoulders). The anterior deltoid also works in tandem with the subscapularis, pecs and lats to internally (medially) rotate the humerus.[19]
The posterior fibers are strongly involved in transverse extension particularly as the latissimus dorsi is very weak in strict transverse extension. Other transverse extensors, the infraspinatus and teres minor, also work in tandem with the posterior deltoid as external (lateral) rotators, antagonists to strong internal rotators like the pecs and lats. The posterior deltoid is also the primary shoulder hyperextensor, more so than the long head of the triceps which also assists in this function.[20]
The lateral fibers perform basic shoulder abduction when the shoulder is internally rotated, and perform shoulder transverse abduction when the shoulder is externally rotated. They are not utilized significantly during strict transverse extension (shoulder internally rotated) such as in rowing movements, which use the posterior fibers.[21]
An important function of the deltoid in humans is preventing the dislocation of the humeral head when a person carries heavy loads. The function of abduction also means that it would help keep carried objects a safer distance away from the thighs to avoid hitting them, as during a farmer's walk. It also ensures a precise and rapid movement of the glenohumeral joint needed for hand and arm manipulation.[2] The lateral fibers are in the most efficient position to perform this role, though like basic abduction movements (such as lateral raise) it is assisted by simultaneous co-contraction of anterior/posterior fibers.[22]
The deltoid is responsible for elevating the arm in the scapular plane and its contraction in doing this also elevates the humeral head. To stop this compressing against the undersurface of the acromion the humeral head and injuring the supraspinatus tendon, there is a simultaneous contraction of some of the muscles of the rotator cuff: the infraspinatus and subscapularis primarily perform this role. In spite of this there may be still a 1–3 mm upward movement of the head of the humerus during the first 30° to 60° of arm elevation.[2]
The most common abnormalities affecting the deltoid are tears, fatty atrophy, and enthesopathy. Deltoid muscle tears are unusual and frequently related to traumatic shoulder dislocation or massive rotator cuff tears. Muscle atrophy is the result of various causes, including aging, disuse, denervation, muscular dystrophy, cachexia and iatrogenic injury. Deltoideal humeral enthesopathy is an exceedingly rare condition related to mechanical stress. Conversely, deltoideal acromial enthesopathy is likely a hallmark of seronegative spondylarthropathies and its detection should probably be followed by pertinent clinical and serological investigation.[23]
The deltoid is also found in apes. The human deltoid is of similar proportionate size as the muscles of the rotator cuff in apes like the orangutan, which engage in brachiation and possess the muscle mass needed to support the body weight by the shoulders. In other apes, like the common chimpanzee, the deltoid is much larger than in humans, weighing an average of 383.3g compared to 191.9g in humans. This reflects the need to strengthen the shoulders, particularly the rotatory cuff, in knuckle walking apes for the purpose of supporting the entire body weight.[2]
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| リンク元 | 「三角筋」「deltoid」 |
| 部位 | 起始 | 停止 | 支配神経 | 機能 | 分布血管 |
| 鎖骨部・前部 | 鎖骨(外側1/3) | 上腕骨(三角粗面) | 腋窩神経 | 肩関節の屈曲、内旋、水平屈曲 | 胸肩峰動脈の三角筋枝 |
| 肩峰部・中部 | 肩甲骨(肩峰) | 肩関節の外転 | |||
| 肩甲棘部・後部 | 肩甲骨(肩甲棘下縁) | 肩関節の外転、伸展、水平伸展 |
Henry Gray (1825-1861). Anatomy of the Human Body. 1918.