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Myology Section 1 the general description The muscle of locomotor system are the skeletal muscles. All of them are attached by at least one end to some part of the skeleton. The skeletal muscle is voluntary muscle undering the voluntary control. About 40% the body weight is shared by the skeletal muscle. The morphology of skeletal muscles belly: consists of muscle fibers and is able to contract tendon: consists of fibrous tissue and is unable to contract According to the shape of muscles: Long muscle Short muscle Flat muscle Orbicular muscle long muscle flat muscle orbicular muscle short muscle digastric The origin, insertion and action of skeletal muscles Origin: the fixed attachment. Insertion: the movable attachment. Agonists: produces most of the force during a particular joint action; Antagonist: oppose the action of a prime mover; Synergist: cooperate in performing an action; Fixators: prevents a bone from moving. Nomenclature of skeletal muscles According to shape: such as deltoid m.; rhomboid m. According to location: such as tibialis ant.; tibialis post. According to origin and insertion: sternocleidomastoid m. According to action: supinator Mixed name: extensor carpi radialis longus flexor carpi radialis The supplementary structures of skeletal muscles 1. Fascia – Superficial fascia It is found in the subcutis in most regions of the body. In different individuals and different part of the body, the thickness is different. Devoid of fatty tissue, there are the trunks of the subcutaneous vessels and nerves, the superficial lymphonotes, the mammary gland and cutaneous muscles. – Deep fascia: It is a dense inelastic fibrous membrane forming a strong investment. intermuscular septum: In the limb, the fasciae give off septa which separate the groups of muscle and attached to the periosteum. retinaculum: the deep fascia is thickened at the wrist and ankle to form the retinaculum that maintains its underlying tendons. 2. Synovial bursa • It is a connective tissue sac with a slippery inner surface, and filled with synovial fluid. • It presents in the place where tendon rubs against bone, ligament, or other tendon, or where skin moves over a body prominence. 3. Synovial sheath of tendon a double layered synovial sheath, in which the tendon runs, is usually located in the hand and foot. Fibrous layer Synovial layer parietal layer visceral layer 4. Sesamoid bones • Be developed in the tendons. • Minimize the friction. • Change the direction of pulling force and strengthen the force of the muscle. Arrangement of muscles • muscles are arranged around the axis of joints: • around coronal axis flexor and extensor • around sagittal axis abductor and adductor • around vertical axis med. and lat. Rotator Section 2 The muscle of trunk The muscles of back The muscle of thorax The diaphragm The muscle of abdomen The muscle of perineum The Muscles of Back Trapezius Superficial group Latissimus dosi Levator scaplae Rhomboid muscle Deep group: concerned with the movement of the vertebral column. Trapezius • Arises from the external occipital protuberance, superior nuchal line, spine of seventh cervical vertebra, cervical ligament, the spinous process and supraspinal ligaments of all thoracic vertebrae. • Be attached to the lateral one third of the clavicle, the acromion and the spine of scapula. • steadies, ascends, descends, retracts and rotates the scapula and extends the head. Latissimus dorsi Arises from the spinous processes of lower six thoracic vertebrae, the thoracolumbar fascia. Be inserted into the floor of the inertubercular sulcus. extends, adducts and medially rotates humerus. Erector spinae It is a collective name for a group of deep muscles of the back. It lines in the vertebral groove on each side of vertebral spines. When acting on one side it bends and rotates the spinal column toward the oppsite side. When acting on both sides it extends the spinal column. The Muscles of Thorax Extrinsic muscles: arise from the outer of the thorax and are insert into the shoulder girdle or the humerus. Intrinsic muscles: be located between the ribs and the sternum or vertebrae. Extrinsic muscles Pectoralis major • Arises from anterior surface of the medial half of the clavicle, the anterior surface of the sternum, the six costal cartilages and the aponeurosis of obliquus externus abdominis. • Inserted into the crest of greater tubercle of humerus. • adducts, flexes and medially rotates arm. Pectoralis minor • Arises from the front of the external surface of the third to fifth ribs • Be inserted into the coracoid process of the scapule. • Stabilizes scapula by drawing it forward and downward. When the scapule is fixed, it helps the inspiration. Serratus anterior • Arises by a series of slips from the external surface of the upper 8-9 ribs. • Be inserted into the entire anterior surface of medial border of the scapula. • Holds the scapula against chest wall and pulls it forward. Intrinsic muscles external intercostal m. pull the ribs upward, increase the thoracic capacity, help inspiration internal intercostal m. pull the ribs downward, decrease the thoracic capacity, help expiration The diaphragm Location: between thoracic and abdominal cavity. structures: peripheral part: muscular part sternal part costal part lumbar part central part: central tendon two weak areas: sternocostal triangle lumbocostal triangle Three openings in the diaphragm Aortic hiatus -12th thoracic vertebra -the abdominal aorta and the thoracic duct Esophageal hiatus -10th thoracic vertebra -the esophagus and the vagal trunks Vena cava foramen -8th thoracic vertebra -the inferior vena cava Diaphragm hernia Action Help Inspiration and assists in raising intra- abdominal pressure. The Muscles of Abdomen obliquus externus abdominis obliquus internus abdominis Anterolateral group Transversus abdominis Rectus abdominis Posterior group：Quadratus lumborum Rectus abdominis obliquus internus abdominis aponeurosis obliquus externus abdominis inguinal ligament Transversus abdominis Tendinous intersections Sheath of rectus abdominis aponeurosis Linea alba The actions of anterolateral group Support and protect the viscera; Maintian and to increase the intrabdominal pressure; Move the vertebral column in flexion, rotation and help to maintain posture. Posterior group Quadratus lumbrum and psoas major Actions: Fixes and lowers the 12th rib; Bends the trunk Extend the lunbar region of the vertebral column. Section 3 The muscles of head and neck The muscles of head Facial muscles Masticatory muscles The facial muscles Characteristic: • Arise from the surface of skull and are inserted onto the skin of the face. • Pull the skin in various directions to express the emotions. • Surrounded the openings act as sphincters and dilators. Epicranius occipitofrontalis Actions: the frontal belly draw the scalp forward, throwing Epicranial aponeurosis the skin of the forehead into Frontal belly transverse wrinkle. The occipital belly draws the scalp backward. Occipital belly orbicularis oculi Muscles around the mouth The masticatory muscles Masseter: elevates and backward pulls the mandible. Temporalis: elevates the mandible. Medial pterygoid: elevates and protrudes mandible. Lateral pterygoid: protrude mandibel and depress chin. The muscles of neck By their positions, the muscles of neck are divided into four groups: superficial, suprahyoid, infrahyoid and deep. I. The superficial group Platysma Actions: tenses skin of neck, draw corners of mouth down, and assists in depressing mandible. Sternocleidomastoid ACTION when acting together turns the head upward； when acting alone the head is inclined laterally and the face is rotated to the opposite side Ⅱ. The hyoid muscles 1. The suprahyoid muscles Action: elevate the hyoid bone and help swallowing. geniohyoid Mylohyoid Stylohyoid Digastric Hyoid bone 2. The infrahyoid muscles Action: depress the hyoid bone. Ⅲ. Deep cervical muscles scalenus anterior scalenus medius scalenus posterior Scalene fissure: above the first rib, between the scalenus anterior and scalenus medius. brachial plexus and subclavian artery pass through it.
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