October 20, 2011
1. In the absence of dystrophin, Ca+2 flows into the cytoplasm. Calcium ions bind to troponin-tropomyosin molecules located in the grooves of the actin filaments. Normally, the rod-like tropomyosin molecule covers the sites on actin where myosin can form crossbridges. Upon binding calcium ions, troponin changes shape and slides tropomyosin out of the groove, exposing the actin-myosin binding sites. Myosin interacts with actin by cycling crossbridges; thereby creating force. Due to the fact that there are no neural pathways opens, Acetylcholine cannot be broken down and Ca+2 is unable to be reabsorbed by the sarcoplasmic reticulum. The exposure to Ca+2 leads to permanent muscle contraction because the actin binding sites are indefinitely open. Some of the dangers associated with forced muscle relaxation is breaking of the bone and muscle tear. The muscles have been in a flexed position for a prolonged amount of time and therefore will require a lot of force to be placed in a relaxed state; causing a tear of muscles and ligaments. Also, the bones associated with those muscles are weak due to a lack of exercise and can easily fracture with a minimal application of force. Most muscle relaxers would be ineffective for treatment because they work along the central nervous system and DMD is independent of that.
2. The muscles that are likely to cause the biggest problems in the shoulder are the deltoid (anterior, posterior, and lateral), supraspinatus, infraspinatus, subscapularis, and teres minor. Next, the muscles that are most likely to causes the biggest problems in the elbow are the biceps brachii long and short head, triceps brachii long and lateral head, brachioradialis, brachialis, and anconeus. Constriction of the muscles listed would not allow an individual to engage in movements required for activities of daily living. The triceps long head originates from the infraglenoid tubercle of the glenoid and the lateral and medial heads originate from the posterior humerus. They all insert into the olecraon process of the ulna and their action is to extend the elbow. The biceps brachii long head originates from the supraglenoid tubercle and the short head originates from the coracoid process; they insert at the radial tuberosity of the radius; and their actions are flexion at the elbow/shoulder and supination at the forearm. The brachioradialis originates at the lateral supracondylar ridge of the humerus; inserts at the styloid process of the radius; and its action is flexion of the forearm. The brachialis originates at the anterior distal half of the humerus; it inserts at the coronoid process of the ulna; its action is also flexion at the forearm. The anconeus originates at the lateral epicondyle of humerus; inserts at the olecranon process of the ulna; and its action extension of the forearm. The deltoid originates from clavicle, acromion, and spine of scapula; it inserts into the deltoid tuberosity of humerus and abducts/flexes/extends at the shoulder. Origin of supraspinatus is supraspinous fossa of scapula; it inserts into greater tubercle of humerus and abducts humerus. Infraspinatus originates from infraspinous fossa and inserts into greater tubercle of humerus; it adducts and laterally rotates shoulder. Subscapularis originates from subscapular fossa of scapula, inserts into lesser tubercle of humerus, and medially rotates shoulder joint. The teres minor originates from superior half of lateral border of scapula and inserts into greater tubercle; it laterally rotates, extends, and adducts at the shoulder. The muscles that I would want to strengthen are the triceps brachii, anconeus supraspinatus, infraspinatus, and teres minor.
3. The muscles that would be affected by lordosis of the lumbar vertebrae are the rectus abdominis, iliacus, psoas muscles, quadratus lumborum, and the erector spinae group. The psoas major originates at the Transverse processes of T12-L5 and the lateral aspects of the discs between them; and inserts into the lesser trochanter of the femur. The psoas minor originates at T12 and L1; and inserts into the pectineal line and iliopectenial eminence. The iliacus originates at the iliac fossa, and inserts into the lesser trochanter of the femur. Quadratus lumborum originates from posterior iliac crest and iliolumbar ligament; it inserts into the twelfth rib and transverse processes of L1-L4. Rectus abdominis originates from pubic crest and inserts into the xyphoid process. The erector spinae originates at the posterior crest of the ilium, lower posterior surface of the sacrum, lower seven ribs, spinous processes of T9-L5, and transverse processes of T1-T12. These muscles insert into the angles of the ribs, transverse processes of all vertebrae, and the base of the skull. Rectus femoris originates from the anterior inferior iliac spine and inserts into the patella, patellar tendon, and tibial tuberosity. The pelvic tilt would be altered in that there would be a noticeable anterior pelvic tilt present with lumbar lordosis. If hip flexor muscles are short or tight, they exert a downward pull on the pelvis resulting in the pelvis being tilted down in front. Hip flexors, erector spinae, and the hamstrings often become tight due to lack of movement. Also, a consistently flexed position puts the muscles in a chronically shortened state. The shortened muscles then begin to exert the downward pull on the pelvis when you are standing. The muscles in the lower leg that would be affected in the walking stride are the hamstrings. With the hip flexors and the hamstrings being tight, there would be a decrease in the degree of knee flexion and hip extension. Both of these movements are extremely crucial in walking since one lifts the leg and the other allows it to move back. Also, the stride would not be consistent with that of a normal walking step because the tightness of the hamstrings and the hip flexors would not allow the leg to be as giving to the motion of walking.