How Many Muscle Consist in Upper limb/Upper Limb Muscle comprises many muscles that are organized into anatomical compartments. These muscles act on the various joints of the hand, arm, and shoulder, maintaining tone, providing stability and allowing precise fluid movement.
Axioappendicular groups of muscles arise from the axial skeleton to act upon the pectoral girdle. Scapulohumeral muscles originate from the scapula and insert into the proximal humerus. Included in this category are the rotator cuff muscles which provide stability to the glenohumeral joint. In the arm, the muscles of the anterior compartment are involved in flexion of the forearm, and the posterior comprises of the forearm extensors. Similarly, the anterior compartment of the forearm contains the flexors of the hand and the posterior has extensors. The hand is divided into the thenar, the hypothenar, the adductor compartment, as well as the short muscles of the hand.[rx][rx][rx][rx][rx]
The upper extremity (UE) is comprised of its associated muscles, nerves, and vessels, organized into anatomical compartments.[rx] The muscles cross joints to provide tone, maintain dynamic joint stability, and perform dynamic functions of the entire extremity. In addition, the arteries and veins provide nourishment and remove waste, and the nerves provide the motor and sensory innervations.[rx]
Types of Muscle of Upper Limb Muscle
PectoralAnterior Axioappendicular Muscles (Thoracoappendicular Muscles)
Pectoral muscles lie in the chest and exert force through the shoulder to move the upper arm. Three pectoral muscles interact with the shoulder.
Pectoralis major
The pectoralis major is a large, fan-shaped muscle covering the chest. It is comprised of clavicular and sternocostal regions.
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Function – flexion, adduction, medial rotation of the humerus.
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Origin – clavicular head: medial clavicle anteriorly, sternocostal head: anterior sternum and costal cartilages of ribs 1 to 6 as well as an external oblique aponeurosis
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Insertion: the lateral edge of the intertrabecular groove of the humerus
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Innervation: medial pectoral nerve (C8, T1) lateral pectoral nerve (C5, C6, C7) of brachial plexus
- Attachments: The clavicular region originates from the clavicle and the sternocostal region originates from the sternum and the fascia of the oblique muscles of the abdomen. Both attach to the humerus.
- Actions: Adducts and rotates the upper arm.
Pectoralis minor
The pectoralis minor muscle is smaller and lies beneath the pectoralis major.
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Function: Depression of the shoulder, protraction of the scapula
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Origin: Third, fourth, fifth ribs close to their respective costal cartilages
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Insertion: Coracoid process
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Innervation: Medial pectoral nerve (C8, T1)
- Attachments: The pectoralis minor originates from the third to fifth ribs and attaches to the scapula.
- Actions: Supports and depresses the scapula.
Subclavius
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Function: Depression and stabilization of the clavicle
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Origin: First rib medially
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Insertion: Middle of the clavicle, inferiorly
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Innervation: Nerve to subclavius (C5, C6)
Serratus anterior
The serratus anterior is located in the lateral wall of the chest.
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Function: Protraction of scapula, rotation of the scapula
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Origin: Lateral first to the eighth rib
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Insertion: anterior scapula, medially
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Innervation: long thoracic nerve (C5, C6, C7)
- Attachments: The muscle is formed of several strips originating from the second to eight ribs, each of which attaches to the scapula.
- Actions: Supports the scapula allowing for elevation of the upper arm.
Posterior Axioappendicular Muscles
Superficial layer
Latissimus dorsi
The latissimus dorsi originates from the lower back and covers a wide area.
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Function: Adduction, medial rotation, an extension of humerus
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Origin: Spinous processes of seventh to 12th thoracic vertebrae, iliac crest, thoracolumbar fascia, and inferior third and fourth rib
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Insertion: Intertubercular groove of humerus
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Innervation: Thoracodorsal nerve (C5,C6,C7)
- Attachments: The latissimus dorsi originates from the lower spine and ribs and the upper pelvis and fascia of the deep trunk muscles. The muscle converges into a tendon attaching to the humerus.
- Actions: Extends, adducts, and medially rotates the upper arm.
Trapezius
The trapezius is the most superficial muscle of the back and forms a broad flat triangle.
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Function: Elevation, depression, and retraction of the scapula, rotation of glenoid cavity
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Origin: Superior nuchal line, nuchal ligament, occipital protuberance, spinous processes of C7- T12
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Insertion: Spine of scapula, acromion, and lateral clavicle
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Innervation: CN XI
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Actions: The superior region supports the arm and elevates and rotates the scapula, the intermediate region retracts the scapula, and the inferior region rotates and depresses the scapula.
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Attachments: The trapezius originates from the skull and spine of the upper back and neck. It attaches to the clavicle and scapula.
Deep Layer
Levator scapulae
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Function: Adduction, medial rotation, an extension of humerus
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Origin: Transverse processes of C1 through C4 vertebrae
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Insertion: Scapula at its medial border
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Innervation: Thoracodorsal nerve (C5, C6, C7)
Rhomboid major
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Function: Retraction of scapula and depression of glenoid cavity
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Origin: Spinous processes of T2 through T5 vertebrae
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Insertion: Inferior aspect of medial scapula
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Innervation: Dorsal scapular nerve (C4, C5)
Rhomboid minor
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Function: Retraction of scapula and depression of glenoid cavity
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Origin: Nuchal ligament as well as spines of C7 and T1 vertebrae
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Insertion: Superior aspect of medial scapula
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Innervation: Dorsal scapular nerve (C4, C5)
Three deep muscles lie below the superficial muscles of the shoulder
Levator Scapulae – A small, strap-like muscle that joins the neck to the scapula.
- Attachments: Originates from the side of the spine in the neck and attaches to the scapula.
- Actions: Elevates the scapula.
Rhomboid Major – Sits inferiorly to the levator scapulae.
- Attachments: Originates from the spine in the upper back and attaches to the scapula in an inferior position to the levator scapulae attachment.
- Actions: Retracts and rotates the scapula.
Rhomboid Minor – Sits between the levator scapulae and rhomboid major, with which it is paired in action and function. It retracts and rotates the scapula.
Scapulohumeral (Intrinsic Shoulder Muscles)
Location of the deltoid muscles
- Highlighted in orange, the deltoids cover the rounding of the shoulder joint. Intrinsic muscles originate from the scapula or clavicle and attach to the humerus. There are six intrinsic muscles, four of which form the rotator cuff.
Deltoid Muscle
The deltoid muscle is a triangular muscle that covers the shoulder. The action of the muscle is complex, with the components acting in opposing and separate ways during the course of a contraction.
- Attachments: The deltoid muscle originates from the scapula and clavicle and attaches to the lateral surface of the humerus.
- Actions: The anterior region assists the pectoralis major during transverse flexion of the shoulder and acts weakly in strict transverse flexion. The lateral region assists in shoulder flexion when the shoulder is rotating, although it also assists the transverse abduction of the shoulder. The posterior region is the hyperextension of the shoulder, contributing to the transverse extension.
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Function: Anterior part: flexion and medial rotation of the arm, middle part: the abduction of arm, posterior part: extension and lateral rotation of the arm
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Origin: Lateral clavicle, acromion and scapular spine
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Insertion: Deltoid tuberosity
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Innervation: Axillary nerve (C5, C6)
Teres major
The teres major is a thick flattened muscle connecting the lower scapula with the humerus.
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Function: Adduction and medial rotation of the arm
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Origin: Posterior surface of scapula at its inferior angle
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Insertion: Intertubercular groove on its medial aspect
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Innervation: Lower scapular nerve (C5, C6)
- Attachments: Originates from the posterior of the scapula and attaches to the humerus.
- Actions: Adducts the shoulder and assists in rotation of the arm.
Supraspinatus
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Function: Initiation of arm abduction
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Origin: Posterior scapula, superior to the scapular spine
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Insertion: Superior aspect of the greater tubercle
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Innervation: Suprascapular nerve (C5, C6)
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Part of rotator cuff muscles
Infraspinatus
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Function: Lateral rotation of arm
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Origin: Posterior scapula, inferior to the scapular spine
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Insertion: Greater tubercle of the humerus, between the supraspinatus and teres minor insertion
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Innervation: Suprascapular nerve (C5, C6)
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Part of rotator cuff muscles
Teres minor
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Function: Lateral rotation of arm
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Origin: Posterior surface of scapula at its inferior angle
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Insertion: Inferior aspect of the greater tubercle
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Innervation: Axillary nerve (C5, C6)
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Part of rotator cuff muscles
Subscapularis
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Function: Adduction and medial rotation of the arm
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Origin: Anterior aspect of the scapula
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Insertion: Lesser tubercle of the humerus
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Innervation: Subscapular nerves (C5, C6, C7)
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Part of rotator cuff muscles
Rotator cuff muscles: supraspinatus, infraspinatus, teres minor, subscapularis
Muscles of Anterior Compartment of Arm (Flexors of Arm)
Biceps brachii –The biceps brachii is a two-headed muscle. Although the majority of the muscle mass is located anteriorly to the humerus, it has no attachment to the bone itself.
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Function: Major flexion of forearm, supination of forearm, resists dislocation of shoulder
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Origin: Short head originates from the coracoid process. The long head is from the supraglenoid tubercle of scapula
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Insertion: Radial tuberosity and forearm fascia (as bicipital aponeurosis)
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Innervation: Musculocutaneous nerve (C5, C6)
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Attachments: Both heads originate from the scapula and attach via the bicipital aponeurosis to the fascia of the forearm.
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Action: Supination of the forearm. It also flexes the arm at the elbow and at the shoulder.
Brachialis – The brachialis muscle lies within the distal region of the biceps brachii.
- Attachments: Originates from the humerus and attaches to the ulna.
- Action: Flexing of the arm at the elbow.
- Function: Flexion of forearm
- Origin: Distal anterior humerus
- Insertion: Coronoid process and ulnar tuberosity
- Innervation: musculocutaneous nerve (C5, C6, C7 small contribution)
Coracobrachialis – The coracobrachialis lies within the two heads of the biceps brachii.
- Attachments: Originates from the scapula and attaches to the humerus.
- Action: Flexing of the arm at the shoulder, and weak adduction
- Function: Flexion and adduction of arm
- Origin: Coracoid process
- Insertion: Middle of the humerus, on its medial aspect
- Innervation: Musculocutaneous nerve (C5, C6, C7)
Muscles of Posterior Compartment of Arm (Extensors of Arm)
Triceps brachii
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Function: Major extensor of the forearm, resists dislocation of the shoulder
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Origin: Lateral head: above the radial groove, medial head: below the radial groove, long head: infraglenoid tubercle of the scapula
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Insertion: Olecranon process of ulna and forearm fascia
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Innervation: Radial nerve (C6,C7,C8)
Anconeus- The anconeus is located in the superficial region of the forearm posterior compartment and is blended with the triceps brachii.
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Function: Extension of the forearm, stabilization of elbow joint
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Origin: Lateral epicondyle of humerus
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Insertion: Olecranon process and posterior ulna
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Innervation: Radial nerve (C7, C8, T1)
- Attachments: Originates from the humerus and attaches to the ulna.
- Actions: Moves the ulna during pronation and extends the forearm at the elbow.
Muscles of Anterior Compartment of Forearm (Flexors of Forearm)
Superficial layer
Pronator Teres – A rectangular muscle located in the superficial region of the anterior compartment.
- Attachments: The pronator teres has two origins, one on the proximal end of the humerus and one of the distal end of the ulna. It attaches to the mid-region of the radius.
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Function: Pronation of radio-ulnar joint and Pronates the forearm.
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Origin: Coronoid process and medial epicondyle of humerus
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Insertion: Lateral surface of the radius
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Innervation: Median nerve (C6, C7)
Pronator Quadratus – A square-shaped muscle located adjacent to the wrist in the deep region of the anterior compartment.
- Attachments: Originates from the ulna and attaches to the radius.
- Action: Pronates the forearm.
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