BACK MUSCLES A- SUPERFICIAL LAYER The superficial layer is formed of two muscles: 1- Trapezius 2- latissimusdorsi
1- Trapezius muscle Origin: External occipital protuberance,superior nuchal line of the occipital bone. From the ligamentumnuchae, the spinous process of the seventh cervical. The spinous processes of all the thoracic vertebrae. Insertion: Posterior border of the lateral third of the clavicle. The medial margin of the acromion. The superior lip of the posterior border of the spine of the scapula.
1- Trapezius muscle Nerve supply: Spinal part of accessory nerve (CN XI). The ventral rami of the third (C3) and fourth (C4)cervical nerves carries proprioception sensation. Action: 1-The upper fibres elevate the shoulder. 2-The lower fibres depress the scapula. 3-The middle fibres retract the scapula.
2- Latissimusdorsimuscle Origin: • spinous processes of T7-T12 • supraspinousligament. • thoracolumbar fascia. • outer lip of iliac crest . • inferior 3 or 4 ribs. • inferior angle of scapula Insertion: Floor of bicipital groove of the humerus. Nerve supply: Nerve to latissmusdorsi(C6,C7,C8). Action: Adducts, extends and medially rotates the arm.
B- DEEP LAYER The deep layer is formed by : 1-levator scapulae 2- Rhomboideusminor 3- Rhomboideusmajor muscles.
1-Levator scapulae muscle Origin: Transverse processes of C1 - C4 vertebrae. Insertion: Medial border of dorsal surface of scapula from the superior angle to the spine. Nerve supply: Dorsal scapular nerve (C5). Action: Elevatesscapula.
2-Rhomboidus minor muscle Origin: Nuchal ligaments and spinous processes of C7 to T1 vertebrae. Insertion: Small area of medial border of dorsal surface of scapula at level of spine. Nerve supply: Dorsal scapular nerve (C5). Action: 1-Retractsthe scapula 2-Rotates the scapula so that the glenoid cavity faces downwards (depress the shoulder).
3-Rhomboideus major muscle Origin: Spinous processes of the T2 to T5 vertebrae. Insertion: Medial border of the scapula, inferior to the insertion of rhomboideus minor muscle. Nerve supply: Dorsal scapular nerve (C5). Action: Retracts the scapula and rotates the scapula so that the glenoid cavity faces downwards.
Supraspinatus muscle Origin: Supraspinous fossa (medial2/3) of scapula. Insertion: Superior facet of greater tuberosity of humerus. Nerve supply: Suprascapular nerve(C5,C6). Action: Abduction of arm from 0˚-18˚.
Infraspinatusmuscle Origin: Infraspinous fossa (medial2/3) of scapula. Insertion: Middle facet at the back of the greater tuberosity of the humerus. Nerve supply: Suprascapularnerve (C5,C6). Action: Lateral rotation of arm.
Teres minor muscle Origin: Lateral border(upper 2/3) of the scapula. Insertion: Inferior facet at the back of the greater tuberosity of the humerus. Nerve supply: Axillary nerve (C5,C6). Action: Lateral rotation and adduction of arm.
Teres major muscle Origin: Posterior aspect of the inferior angle of the scapula. Insertion: Medial lip of bicipital groove of the humerus. Nerve supply: Lower subscapular nerve (C5,C6). Action: Medial rotation,adduction and extension of the humerus.
Subscapularismuscle Origin: Subscapular fossa (medial 2/3). Insertion: Lesser tuberosity of humerus. Nerve supply: Upper andlower subscapular nerves (C5, C6). Action: Rotates the humerus medially.
Deltoid muscle Origin: anteriorborder of lateral 1/3 of clavicle. ,lateral margin of the acromion and crest of the spine of the scapula. Insertion: Into deltoid tuberosity on the middle of the lateral aspect of the shaft of the humerus. Nerve supply: Axillary nerve (C5, C6). Action: • Anterior fibers: flexion and medial rotation of humerus. • Middle fibers: abduction from1 8˚-90˚. • Posterior fibers: extension and lateral rotation of humerus.
ROTATOR CUFF MUSCLES • Rotator cuff muscles surround the shoulder joint, they include: • Subscapularis. • Supraspinatus. • Infraspinatus. • Teres minor.
INTERMUSCULAR SPACES 1- Quadrangular space: Boundaries It is bounded by: Superiorly: Teres minor. Inferiorly: Teres major. Medially: the long head of the Triceps brachii. Laterally: the surgical neck of the humerus. Contents It transmits the axillary nerve and posterior circumflex humeral artery.
2-Medial triangular space Boundaries: Teres minor superiorly. Teresmajor inferiorly. Long head of the Triceps laterally. Contents: It contains the circumflex scapular vessels.
3- Lateral triangular space Boundaries: Teres major superiorly. Long head of the Triceps medially. Humerus laterally. Contents: The radial nerve and profundabrachii artery.