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Monday, March 2, 2015

The movement of body structures

The movement of body structures is accomplished by the contraction of muscles. Muscles may move parts of the skeleton relatively to each other, or may move parts of internal organs relatively to each other. All such movements are classified by the directions in which the affected structures are moved. In human anatomy, all descriptions of position and movement are based on the assumption that the body is in its complete medial and abduction stage and is in anatomical position.

Most terms of a motion have clear opposites, and as such, are treated below in pairs.

General motion:

Flexion – Bending movement that decreases the angle between two parts. Bending the elbow, or clenching a hand into a fist, are examples of flexion. When sitting down, the knees are flexed. Flexion of the hip or shoulder moves the limb forward (towards the anterior side of the body). Good examples of hip flexors are the rectus femoris, sartorius, iliacus, and psoas. Some knee flexors are the biceps femoris, semitendinosus, and semimembranosus, and some elbow flexors are the brachialis, biceps brachii, and brachioradialis.

Extension – The opposite of flexion; a straightening movement that increases the angle between body parts. In a conventional handshake, the fingers are fully extended. When standing up, the knees are extended. Extension of the hip or shoulder moves the limb backward (towards the posterior side of the body). Elbow extensors include the triceps brachii and anconeus. The main muscles that extends the hip is the gluteus maximus. The muscles that extend the knee are the quadriceps group: the rectus femoris, vastus lateralis, vastus medialis, and vastus intermedius.

Abduction – A motion that pulls a structure or part away from the midline of the body (or, in the case of fingers and toes, spreading the digits apart, away from the centerline of the hand or foot). Abduction of the wrist is called radial deviation. Raising the arms laterally is an example of abduction. A good example for the arm is the deltoid. Some leg abductors are the gluteus medius and the gluteus minimus.

Adduction – A motion that pulls a structure or part toward the midline of the body, or towards the midline of a limb. Dropping the arms to the sides, or bringing the knees together, are examples of adduction. In the case of the fingers or toes, adduction is closing the digits together. Adduction of the wrist is called ulnar deviation. The inner thigh houses some adductors, including the adductor brevis, adductor longus, adductor magnus, and pectineus. The latissimus dorsi is a good example for the humerus.

Internal rotation (or medial rotation) of the shoulder or hip would point the toes or the flexed forearm inwards (towards the midline). The pectoralis major and subscapularis both medially rotate the humerus. The adductor longus and adductor brevis both medially rotate the thigh.

External rotation (or lateral rotation) is the opposite of internal rotation. It would turn the toes or the flexed forearm outwards (away from the midline). The sartorius laterally rotates the femur. The infraspinatus and teres minor both laterally rotate the humerus.

Elevation – Movement in a superior direction. The upper muscle fibers of the trapezius aid in elevating the apex of the shoulder.

Depression – Movement in an inferior direction, the opposite of elevation. Opposite to the upper fibers, the lower half of the trapezius aids in depressing the apex of the shoulder.




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