MedicoPlexus
Human Anatomy & Histology
248. Deltoid region.
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.
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”.
The deltoid originates in three distinct sets of fibers, often referred to as “heads”:
The anterior or clavicular fibers arises from most of the anterior border and upper surface of the lateral third of the clavicle. The anterior origin lies adjacent to the lateral fibers of the pectoralis major muscle as do the end tendons of both muscles. These muscle fibers are closely related and only a small chiasmatic space, through which the cephalic vein passes, prevents the two muscles from forming a continuous muscle mass.
The anterior deltoids are commonly called front delts for short.
Lateral or acromial fibers arise from the superior surface of the acromion process of the scapula. They are commonly called lateral deltoid. This muscle is also called middle delts, outer delts, or side delts for short.
They are also mistakenly called medial deltoid, which is wrong, as their origin is the least medial portion of the deltoid.
Posterior or spinal fibers arise from the lower lip of the posterior border of the spine of the scapula. They are commonly called posterior deltoid or rear deltoid (rear delts for short
Insertion
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 gives 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.
Blood supply
The deltoid is supplied by the posterior circumflex humeral artery and the deltoid branch of the thoracoacromial artery which branches from the axillary artery.
Innervation
The deltoid is innervated by the axillary nerve. 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.
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.
249. Anterior brachial region. 250. Posterior brachial region. 251. Elbow (regions cubiti). 252. Anterior forearm region. 253. Posterior forearm region. 254. Wrist region.255. Palm of the hand.256. Dorsum of the hand.
In formal usage, the term “arm” only refers to the structures from the shoulder to the elbow, explicitly excluding the forearm, and thus “upper limb” and “arm” are not synonymous.
Musculoskeletal system- Shoulder girdle-
Bones of the shoulder girdle
Main article: Shoulder girdle
The shoulder girdle- or pectoral girdle,- composed of the clavicle and the scapula, connects the upper limb to the axial skeleton through the sternoclavicular joint (the only joint in the upper limb that directly articulates with the trunk), a ball and socket joint supported by the subclavius muscle which acts as a dynamic ligament. While this muscle prevents dislocation in the joint, strong forces tend to break the clavicle instead. The acromioclavicular joint, the joint between the acromion process on the scapula and the clavicle, is similarly strengthened by strong ligaments, especially the coracoclavicular ligament which prevents excessive lateral and medial movements. Between them these two joints allow a wide range of movements for the shoulder girdle, much because of the lack of a bone-to-bone contact between the scapula and the axial skeleton. The pelvic girdle is, in contrast, firmly fixed to the axial skeleton, which increases stability and load-bearing capabilities. –
The mobility of the shoulder girdle is supported by a large number of muscles. The most important of these are muscular sheets rather than fusiform or strap-shaped muscles and they thus never act in isolation but with some fibres acting in coordination with fibres in other muscles.-
Muscles
of shoulder girdle excluding the glenohumeral joint-
Migrated from head
Trapezius, sternocleidomastoideus, omohyoideus
Posterior
Rhomboideus major, rhomboideus minor, levator scapulae Anterior
Subclavius, pectoralis minor, serratus anterior Shoulder joint-
Shoulder joint with ligaments
The glenohumeral joint (colloquially called the shoulder joint) is the highly mobile ball and socket joint between the glenoid cavity of the scapula and the head of the humerus. Lacking the passive stabilization offered by ligaments in other joints, the glenohumeral joint is actively stabilized by the rotator cuff, a group of short muscles stretching from the scapula to the humerus. Little inferior support is available to the joint and dislocation of the shoulder almost exclusively occurs in this direction. –
The large muscles acting at this joint perform multiple actions and seemingly simple movements are often the result of composite antagonist and protagonist actions from several muscles. For example, pectoralis major is the most important arm flexor and latissimus dorsi the most important extensor at the glenohumeral joint, but, acting together, these two muscles cancel each other’s action leaving only their combined medial rotation component. On the other hand, to achieve pure flexion at the joint the deltoid and supraspinatus must cancel the adduction component and the teres minor and infraspinatus the medial rotation component of pectoralis major. Similarly, abduction (moving the arm away from the body) is performed by different muscles at different stages. The first 10° is performed entirely by the supraspinatus, but beyond that fibres of the much stronger deltoid are in position to take over the work until 90°. To achieve the full 180° range of abduction the arm must be rotated medially and the scapula most be rotate about itself to direct the glenoid cavity upward. –
Muscles
of shoulder joint proper- Posterior
Supraspinatus, infraspinatus, teres minor, subscapularis, deltoideus, latissimus dorsi, teres major
Anterior
Pectoralis major, coracobrachialis Arm-
Superficial muscles of the arm
Main article: Arm
The arm proper (brachium), sometimes called the upper arm,- the region between the shoulder and the elbow, is composed of the humerus with the elbow joint at its distal end.
The elbow joint is a complex of three joints — the humeroradial, humeroulnar, and superior radioulnar joints — the former two allowing flexion and extension whilst the latter, together with its inferior namesake, allows supination and pronation at the wrist. Triceps is the major extensor and brachialis and biceps the major flexors. Biceps is, however, the major supinator and while performing this action it ceases to be an effective flexor at the elbow. –
Muscles
of the arm-
Posterior
Triceps brachii, anconeus
Anterior
Brachialis, biceps brachii
Forearm-
Ventral superficial muscles of the forearm
Main article: Forearm
The forearm (antebrachium),- composed of the radius and ulna; the latter is the main distal part of the elbow joint, while the former composes the main proximal part of the wrist joint.
Most of the large number of muscles in the forearm are divided into the wrist, hand, and finger extensors on the dorsal side (back of hand) and the ditto flexors in the superficial layers on the ventral side (side of palm). These muscles are attached to either the lateral or medial epicondyle of the humerus. They thus act on the elbow, but, because their origins are located close to the center of rotation of the elbow, they mainly act distally at the wrist and hand. Exceptions to this simple division are brachioradialis — a strong elbow flexor — and palmaris longus — a weak wrist flexor which mainly acts to tense the palmar aponeurosis. The deeper flexor muscles are extrinsic hand muscles; strong flexors at the finger joints used to produce the important power grip of the hand, whilst forced extension is less useful and the corresponding extensor thus are much weaker. –
Biceps is the major supinator (drive a screw in with the right arm) and pronator teres and pronator quadratus the major pronators (unscrewing) — the latter two role the radius around the ulna (hence the name of the first bone) and the former reverses this action assisted by supinator. Because biceps are much stronger than its opponents, supination is a stronger action than pronation (hence the direction of screws). –
Muscles
of the forearm-
Posterior
(Superficial) extensor digitorum, extensor digiti minimi, extensor carpi ulnaris, (deep) supinator, abductor pollicis longus, extensor pollicis brevis, extensor pollicis longus, extensor indicis Anterior
(Superficial) pronator teres, flexor digitorum superficialis, flexor carpi radialis, flexor carpi ulnaris, palmaris longus, (deep) flexor digitorum profundus, flexor pollicis longus, pronator quadratus Radial
Brachioradialis, extensor carpi radialis longus, extensor carpi radialis brevis Wrist[
Main article: Wrist
The wrist (carpus),- composed of the carpal bones, articulates at the wrist joint (or radiocarpal joint) proximally and the carpometacarpal joint distally. The wrist can be divided into two components separated by the midcarpal joints. The small movements of the eight carpal bones during composite movements at the wrist are complex to describe, but flexion mainly occurs in the midcarpal joint whilst extension mainly occurs in the radiocarpal joint: the latter joint also providing most of adduction and abduction at the wrist. –
How muscles act on the wrist is complex to describe. The five muscles acting on the wrist directly — flexor carpi radialis, flexor carpi ulnaris, extensor carpi radialis, extensor carpi ulnaris, and palmaris longus — are accompanied by the tendons of the extrinsic hand muscles (i.e., the muscles acting on the fingers). Thus, every movement at the wrist is the work of a group of muscles; because the four primary wrist muscles (FCR, FCU, ECR, and ECU) are attached to the four corners of the wrist, they also produce a secondary movement (i.e., ulnar or radial deviation). To produce pure flexion or extension at the wrist, these muscle therefore must act in pairs to cancel out each other’s secondary action. On the other hand, finger movements without the corresponding wrist movements require the wrist muscles to cancel out the contribution from the extrinsic hand muscles at the wrist. –
Hand
Bones of the hand
Main article: Hand
The hand (manus),- the metacarpals (in the hand proper) and the phalanges of the fingers, form the metacarpophalangeal joints (MCP, including the knuckles) and interphalangeal joints (IP).
Of the joints between the carpus and metacarpus, the carpometacarpal joints, only the saddle-shaped
joint of the thumb offers a high degree of mobility while the opposite is true for the metacarpophalangeal joints. The joints of the fingers are simple hinge joints. –
The primary role of the hand itself is grasping and manipulation; tasks for which the hand has been adapted to two main grips — power grip and precision grip. In a power grip an object is held against the palm and in a precision grip an object is held with the fingers, both grips are performed by intrinsic and extrinsic hand muscles together. Most importantly, the relatively strong thenar muscles of the thumb and the thumb’s flexible first joint allows the special opposition movement that brings the distal thumb pad in direct contact with the distal pads of the other four digits. Opposition is a complex combination of thumb flexion and abduction that also requires the thumb to be rotated 90° about its own axis. Without this complex movement, humans would not be able to perform a precision grip. –
In addition, the central group of intrinsic hand muscles give important contributions to human dexterity.
The palmar and dorsal interossei adduct and abduct at the MCP joints and are important in pinching. The lumbricals, attached to the tendons of the flexor digitorum profundus (FDP) and extensor digitorum communis (FDC), flex the MCP joints while extending the IP joints and allow a smooth transfer of forces between these two muscles while extending and flexing the fingers. –
Metacarpal
Lumbricals, palmar introssei, dorsal interossei
Thenar
Abductor pollicis brevis, adductor pollicis, flexor pollicis brevis, opponens pollicis Hypothenar
Abductor digiti minimi, flexor digiti minimi, opponens digiti minimi, palmaris brevis
Neurovascular system Innervation-Branches of brachial plexus
The motor and sensory supply of the upper limb is provided by the brachial plexus which is formed by the ventral rami of spinal nerves C5-T1. In the posterior triangle of the neck these rami form three trunks from which fibers enter the axilla region (armpit) to innervate the muscles of the anterior and posterior compartments of the limb. In the axilla, cords are formed to split into branches, including the five terminal branches listed below. – The muscles of the upper limb are innervated segmentally proximal to distal so that the proximal muscles are innervated by higher segments (C5–C6) and the distal muscles are innervated by lower segments (C8–T1).
Motor innervation of upper limb by the five terminal nerves of the brachial plexus:
The musculocutaneous nerve innervates all the muscles of the anterior compartment of the arm. The median nerve innervates all the muscles of the anterior compartment of the forearm except flexor carpi ulnaris and the ulnar part of the flexor digitorum profundus. It also innervates the three thenar muscles and the first and second lumbricals.
The ulnar nerve innervates the muscles of the forearm and hand not innervated by the median nerve.
The axillary nerve innervates the deltoid and teres minor.
The radial nerve innervates the posterior muscles of the arm and forearm Collateral branches of the brachial plexus:
The dorsal scapular nerve innervates rhomboid major and minor.
The long thoracic nerve innervates serratus anterior.
The suprascapular nerve innervates supraspinatus and infraspinatus
The lateral pectoral nerve innervates pectoralis major
The medial pectoral nerve innervates pectoralis major and minor
The upper subscapular nerve innervates subscapularis
The thoracodorsal nerve innervates latissimus dorsi
The lower subscapular nerve innervates subscapularis and teres major the medial brachial cutaneous nerve innervates the skin of medial arm
The medial antebrachial cutaneous nerve innervates the skin of medial forearm
257. Gluteal region.
The Superficial Muscles
The superficial muscles in the gluteal region consist of the three glutei and the tensor fascia lata. They act mainly act to abduct and extend the lower limb at the hip joint.
Gluteus Maximus
The gluteus maximus is the largest of the gluteal muscles. It is also the most superficial, producing the shape of the buttocks.
Attachments: Originates from the gluteal (posterior) surface of the ilium, sacrum and coccyx. It slopes across the buttock at a 45-degree angle, then inserts into the iliotibial tract and the gluteal tuberosity of the femur.
Actions: It is the main extensor of the thigh and assists with lateral rotation. However, it is only used when force is required, such as running or climbing.
Innervation: Inferior gluteal nerve.
Gluteus Medius
The gluteus medius muscle is fan-shaped and lies between to the gluteus maximus and the mnimus. It is similar is shape and function to the gluteus minimus.
Attachments: Originates from the gluteal surface of the ilium and inserts into the lateral surface of the greater trochanter.
Actions: Abducts and medially rotates the lower limb. During locomotion, it secures the pelvis, preventing pelvic drop of the opposite limb. (Note: the posterior fibres of the gluteus medius are also thought to produce a small amount of lateral rotation).
Innervation: Superior gluteal nerve.
Gluteus Minimus
The gluteus minimus is the deepest and smallest of the superficial gluteal muscles. It is similar is shape and function to the gluteus medius.
Attachments: Originates from the ilium and converges to form a tendon, inserting to the anterior side of the greater trochanter.
Actions: Abducts and medially rotates the lower limb. During locomotion, it secures the pelvis, preventing pelvic drop of the opposite limb.
Innervation: Superior gluteal nerve.
Tensor Fascia Lata
Tensor fasciae lata is a small superficial muscle which lies towards the anterior edge of the iliac crest. It functions to tighten the fascia lata, and so abducts and medially rotates the lower limb.
Attachments: Originates from the anterior iliac crest, attaching to the anterior superior iliac spine (ASIS). It inserts into the iliotibial tract, which itself attaches to the lateral condyle of the tibia.
Actions: Assists the gluteus medius and minimus in abduction and medial rotation of the lower limb. It also plays a supportive role in the gait cycle. Innervation: Superior gluteal nerve.
Open resource