Flashcards in TBL 4 - Long Bone Formation, Shoulder Joint, Intrinsic Shoulder Muscles, Posterior Arm Muscles, and Muscle Tissue Deck (63):
Which mesodermic layer generates the chondroblasts and osteoblasts that form the scapula, clavicle, and bones of the upper limb?
The parietal mesodermic layer
What is the first step of endochondral ossification?
Thin bony collars form around the diaphysis (shaft) of cartilaginous replicas. The chondrocytes are separated from the capillaries in the perichondrium causing the cartilage to start degrading
Describe the primary ossification center
Osteoblasts, angiogenic capillaries and macrophages from the bony collar periosteum enter the diaphysis and replace the cartilage with trabecular bone
What is the epiphysis
Ends of the diaphysis where chondrocytes are proliferating creating longitudinal growth plates at the junction of the epiphysis and diaphysis
Why is achondroplasia associated with skeletal dysplasia e.g., dwarfism?
The misformed cartilage causes the bones to be misinformed as the replicas are wrong.
In neonates, what does the residual trabecular bone in the diaphysis become?
What eventually forms in the epiphysis
Secondary ossification centers
Up to what period do growth plates remain active and when does bony union occur?
Active during puberty. Bony union occurs at skeletal maturity
What forms the basic shoulder joint?
1/3 of Head of humerus with glenoid cavity of scapula
What is the glenoid labrum and what surrounds the joint?
Concentric rings of Type I collagen that attaches to the rim of glenoid cavity to deepen it slightly and accept more of the humerus. A capsule of loose connective tissue surrounds the joint
How would loss of rotator cuff muscle tone affect the glenohumeral joint?
The rotator cuff muscle tonus is important to holding the joint together. Loss of tone would result in more dislocations as is common during anesthesia
What covers the superior side of the glenohumeral joint?
The acromioclavicular joint formed by the articulation of the acromion with the lateral end of the clavicle
What does the AC joint do? (acromioclavicular)
Allows clavicle to act as a strut. Suspends scapula and allows it to slide along posterior thoracic wall enabling greater freedom of motion
What prevents the superior displacement of the joint from the glenoid cavity?
The coraco-acromial ligament connects the coracoid process and accordion forming a strong arch over the humeral head
What does the acromioclavicular ligament do
Reinforces superior aspect of the AC joint
What does the coracoclavicular ligament do
Stronger than acromioclavicular ligament and prevents dislocation of AC joint
Why do forceful superior thrusts of the humerus typically fail to dislocate the glenohumeral joint but fracture the humeral shaft or clavicle?
The humeral shaft or clavicle breaks before the coraco-acromial ligament
Why do movements of the medial and lateral fragments of a fractured clavicle result in dropping of the shoulder? What is a greenstick fracture?
The trapezius is unable to hold up the lateral fragment because of the weight of the upper limb.
Greenstick fracture occurs in children in immature bone where the bone bends but does not completely break
When does dislocation of the acromioclavicular joint occur and why does physical examination of the injury lead to its description as a “shoulder separation”?
Direct blow to the superolateral side of back or hard fall on shoulder/outstretched upper limb. It is described as a shoulder separation because when the coracoclavicular ligament tears, the shoulder separates from the clavicle and drops because of the weight.
Why do most dislocations of the humeral head occur in an inferior direction, and why are such dislocations commonly described clinically as anterior dislocations?
The coraco-acromial arch and rotator cuff muscles prevent upward dislocation so inferior dislocation is common. They are described as anterior because the head of the humerus goes anterior to the glenoid cavity (anterior to the infraglenoid tubercle and long head of triceps)
Deltoid - lateral third of clavicle, accordion, and spine of scapula to the deltoid tuberosity
What does the axillary nerve innervate?
Deltoid, teres minor
How is the axillary nerve commonly injured at the surgical neck of the humerus, and where does loss of sensation occur after the injury?
It courses inferior to the humeral head and around the surgical neck meaning that it would get injured if the humerus fractures or glenohumeral joint dislocates. Also can be compressed when crutches are used improperly. Loss of sensation is on the lateral side of the proximal part of the arm supplied by the superior lateral cutaneous nerve of the arm.
What are the roles of the anterior and posterior portion of the deltoid during walking
Anterior part flexes the arm with help from the coracobrachialis
Posterior part extends the arm
What muscles abduct the arm
Deltoid with help from the supraspinatous (first 15 degrees)
Inferior angle of scapula to medial surface of humerus
What muscles medially rotate the arm? Laterally?
Teres major and subscapularis. Infraspinatous and teres minor
Supraspinatus and infraspinatus
Supra scapular fossa and infraspinatus to greater tubercle of humerus
What is the role of the subacromial bursa
Fluid filled and cushions the supraspinatus tendon as it courses between the humeral head and osseoligamentous coraco-acromial arch toward the greater tubercle
What does the suprascapular nerve innervate?
The supraspinatus and infraspinatus
lateral border of the scapula to the greater tubercle of the humerus
Anterior surface of the scapula to the less tubercle of the humerus
What does the lower subscapular nerve innervate?
Teres major and subscapularis, both medial rotators of the arm
Why is the upper limb pulled into medial rotation after an avulsion fracture of the greater tubercle?
The muscles still attached, namely the subscapularis and teres major are still attached to medially rotate the arm
What is the painful arc syndrome?
Inflammation and calcification of the subacromial bursa. The lesion contacts the inferior surface of the accordion causing pain while abducting arm between 50 and 130 degrees
How is degenerative tendinitis of the rotator cuff tested?
The person slowly adducts a fully abducted arm. At 90 degrees, the arm will uncontrollably drop if rotator cuff is damaged
Long head - infraglenoid tubercle
Lateral head - above radial groove of humerus
Medial head - below radial groove of humerus
Distal - olecranon of proximal ulna
What does the radial nerve innervate
Function of each head of triceps
Long - prevent inferior displacement of humeral head
Medial - workhorse for forearm extension
Lateral head - stronger but only necessary when encountering resistance
Why is forearm extension weakened but not lost after fracture along the radial groove of the humerus?
Radial groove on posterior of humerus is where the nerve courses. Only medial head is affected as the long and lateral connect above the radial groove to the nerve.
Intrinsic back muscles and extrinsic shoulder muscles come from which mesoderm layer
Muscles of the upper limb and intrinsic shoulder muscles come from which mesoderm layer
Parietal of lateral plate
Describe the development of muscle tissue.
At 4 weeks, myoblasts line up in rows and at 5 weeks, they fuse into myotubes. They develop into fibers with actin and myosin appeared. The longitudinal sections of the fibers displays cross striations of myofilaments into myofibrils
Describe the sarcomere
Successive Z bands delineate it. I bands at the end are the actin. M band in the middle is the myosin. The A band is where actin and myosin connect. Z band is where the thin filaments anchor.
What are T tubules and what do they do?
There are invaginations of the muscle cell membrane (sarcolemma) and carry signals from the sarcolemma to the interior of the muscle cell. They form triads with the sarcoplasmic reticulum
Describe the synapse of a muscle fiber with a motor axon
Acetylcholine is released from the axon terminal, binds the sarcolemma, and induces muscle contraction
What do satellite cells for muscles do?
Sit along the sarcolemma. They are reserve stem cells/resting myoblasts that repair damaged muscle or help with growth. They are more active in slow-twitch muscles
How does EMG test muscle action?
Electromyography tests muscle action by measuring the difference in electric action potentials between resting muscle and contracting muscle
What is the deficiency that causes Duchenne muscular dystrophy and what are the symptoms of this disease?
Dystrophin deficiency which is a membrane-associated cytoskeletal protein that maintains integrity during contraction. Symptoms include rapid progression of skeletal muscle degeneration, weakness in muscle, worsens with age
How does the common hereditary disorder myasthenia gravis affect the induction of postsynaptic action potentials?
It is an autoimmune disease that involves distortion of the sarcolemma at the postsynaptic side. The concentration of acetylcholine receptors is decreased because of antibodies making it less sensitive to acetylcholine
Type I muscle fibers
Slow-twitch, fatigue resistant. Used in muscles that use little force, posture muscles, walking
Type IIA muscle fibers
Fast-twitch, fatigue resistant. Marathon runners
Type IIB muscle fibers
Fast-twitch, fatiguable, glycolytic, sprinters
Dense connective tissue surrounding the whole muscle
Dense connective tissue surrounding fascicles of muscle fibers
Loose connective tissue around each fiber
Dense connective tissue with Type I collagen and fibroblasts and capillaries intervening. They are continuations of the epimysium and distally, continuous with the fibrous layer of periosteum
Why are skeletal muscles trained according to their percentages of fiber types?
Train them based on the type of fibers they should contain.
Why are muscle-tendon junctions more susceptible to strain injuries in children?
The junction is an area of rapidly growing muscle fiber so it cannot sustain very strong forces leading to more injury
What mesodermic layer forms the smooth muscle
Mesenchymal cells of the visceral layer
Describe smooth muscle fibers
Staggered to closely pack. Actin bind dense bodies attached to the inner surface of sarcolemma scattered within the sarcoplasm. Myosin associates with actin to create filament sliding
How are smooth muscle contractions triggered?
Varicosities along postsynaptic sympathetic fibers release norepinephrine that binds the sarcolemma. Gap junctions between muscle fibers allow the action potential to spread resulting in synchronous conduction