TBL 4 Objectives

Question 1

Describe the glenohumeral joint and glenoid labrum

Answer 1

glenohumeral joint: (shoulder) is formed by the articulation of the head of humerus with the glenoid cavity of the scapula

glenoid labrum: made of concentric rings of type I collagen fibers. It attaches to the rim of the cavity to slightly, but effectively deepen it

Question 2

Distinguish the acromioclavicular joint and coraco-acromial arch

Answer 2

Acromioclavicular joint (AC joint) is the articulation of of the acromion with the lateral head of the clavicle. It is located above the glenohumeral joint

coraco-acromial arch: the coco-acromial ligament connects the caracoid process and acromion. The arch overlies the humeral head and prevents superior dislocation

Question 3

Describe the strut function of the clavicle and the coracoclavicular ligament

Answer 3

The AC joint allows the clavicle to act as a strut (suspending the scapula) and allowing it to slide along the posterior thoracic wall.

Question 4

1. Why do forceful superior thrusts of the humerus typically fail to dislocate the glenohumeral joint, but fracture the humeral shaft or clavice?
2. Why do movements of the medial and lateral fragments of a fractured clavice result in dropping of the shoulder? What is a greenstick fracture?
3. When does dislocation of the acromioclavicular joint occur and why does the physical examination of the injury lead to its description as a “shoulder separation”?

Answer 4

1. The coraco-acromial arch is so strong that the humerus or clavicle will break first
2. The sternocloidomastoid muscle pulls the medial fragment of the clavice upwards. The trapezius is unable to hold the lateral fragment up. The pectoris pulls the lateral fragment medially
3. Although the coracoclavicular ligament is strong, the AC joint is weak and easily injured. An AC joint dislocation (often called a shoulder separation) is severe when AC and coracoclavicular ligaments are both torn. When coracoclavicular ligament is tears, the shoulder separates from the clavicle and falls because of the weight of the upper limb

Question 5

Name the intrinsic shoulder muscles

Answer 5

rotator cuff, deltoid, teres major

Question 6

Cite bony attachments and innervations of the intrinsic muscles

Answer 6

already made notecards for these

Question 7

Recollect the process of endochondral ossification

Answer 7

Endochondral ossification is the formation of bone tissue via cartilage displacement.

Chondroblasts, which originate from mesenchymal stem cells, produce avascular cartilaginous replicas of the bones. Blood vessels invade the avascular cartilaginous matrix, bringing osteoblasts, angiogenic capillaries, and macrophages. This restricts proliferating chondrocytes to the epiphyses of the bones. Chondrocytes near the diaphyses undergo hypertrophy and apoptosis as they mineralize the surrounding matrix. Osteoblasts bind to the mineralized matrix and deposit bone.

Mesenchymal cells of paraxial mesoderm-derived somites generate chondroblasts and osteoblasts that form the vertebral column via endochondral ossification

Mesenchymal cells of the parietal layer generate chondroblasts and osteoblasts that form the scapula, clavicle, and bones of the upper limb.

Question 8

Describe the bony collar and primary center of ossification

Answer 8

Endochondral ossification of long bones begins by formation of thin bony collars around the diaphysis of the cartilaginous replicas. These bony collars initiate degradation of the replicas by separating chondrocytes from capillaries in the perichondrium.

Osteoblasts, angiogenic capillaries, and macrophages from the bony collar periosteum enter the diaphysis and replace eroded cartilage with trabecular bone that creates the primary ossification center in the diaphysis.

Question 9

Describe the growth (aka epiphyseal) plates

Answer 9

The epiphyses is located at the ends of the diaphysis. Proliferation of epiphyseal chondrocytes creates growth aka epiphyseal plates, which are organized in longitudinal cellular columns at the junctions of the epiphyses with the diaphyses.
Chondrocytes in these longitudinal columns that are next to the diaphysis degenerate and at the same time, expansion of trabecular bone of the primary ossification center expands to replace the eroding cartilage. This progressive replacement lengthens the developing long bone.

Question 10

Describe secondary centers of ossification

Answer 10

Secondary centers of ossification form in the epiphyses, which begins their ossification. When completed, cartilage remains only in the epiphyseal plates.

Question 11

Cite when bony union of the epiphyses with the diaphysis occurs.

Answer 11

Bony union of the epiphyses with the diaphysis occurs at skeletal maturity.
Before that, at age 10, the epiphyses mature into cores of trabecular bone covered by compact bone while the growth plates remain active during puberty.

Question 12

Why is achondroplasia associated with skeletal dysplasia?

Answer 12

In achondroplasia, there is a problem with ossification (converting the cartilage into bone) particularly in the long bones of the arms and legs.
There is a growth receptor whose normal function is to inhibit bone growth. In achondroplasia, this growth receptor is mutated so that it is activated all the time, and skeletal dysplasia results.

Question 13

Subacromial bursa

Answer 13

Cushions supraspinatus tendon between humeral head and coraco-acromial arch.

Question 14

Triceps

Answer 14

Proximal Attachment:
Long Head: Infraglenoid tubercle, helps resist inferior displacement of humeral head
Medial Head: posterior humerus distal to radial groove
Lateral Head: posterior humerus proximal to radial groove
Distal attachment:Olecranon (of ulna; passes over elbow joint.
Innervation: Radial nerve (as it courses through the radial groove).
Function:
Long head: crosses glenohumeral joint and helps resist displacement of the humeral head.
Medial head: work horse of forearm extension
Lateral head: Recruited for counter resistance against extension

Question 15

What is the physical appearance of the shoulder after axillary nerve injury at the surgical neck of the humerus and where does loss of sensation occur?

Answer 15

The deltoid atrophies when the axillary nerve (C5, C6) is damaged. The axillary nerve winds around the surgical neck of the humerus and is usually injured during fracture of this part of the humerus. As a results of deltoid atrophy, the rounded contour of the shoulder is flattened compared to the uninjured side. This gives the shoulder a flattened appearance and produces a slight hollow inferior to the acromion.
Loss of sensation can be experienced of the lateral side of the proximal arm that is supplied by a branch of the axillary nerve.

Question 16

Why is the upper limb pulled into medial rotation after an avulsion fracture of the greater tubercle?

Answer 16

The greater tubercle is the distal attachment of the infraspinatus and the teres minor muscles, both of which act to rotate the limb laterally. With loss of tonus of these two muscle, the subscapularis muscle, which attaches distally to the lesser tubercle and the teres major, which attached distally to the middle tip of the intertubercular sulcus, both act to rotate the limb medially.

Question 17

What is the painful arc syndrome?

Answer 17

Calcific supraspinatus tendinitis is inflammation and calcification of the subacromial bursa, which results in pain, tenderness, and limitation of movement of the glenohumeral joint. As long as the glenohumeral joint is adducted, no pain usually results because in this position the painful lesion is away from the inferior surface of the acromion. In more people, the pain occurs during 50 to 130 degress of abduction, which is known as painful arc syndrome. This is a result of during this arc, the supraspinatus tendon is in intimate contact with the inferior surface of the acromion.

Question 18

How is degenerative tendinitis of the rotator cuff tested?

Answer 18

Degenerative tendonitis is a result of humeral head and rotator cuff impingement on the coraco-acromial arch, producing irritation of the arch and inflammation of the rotator cuff. The test for this condition is the person is asked to lower the fully abducted limb slowly and smoothly. From about 90 degrees abduction, the limb will suddenly drop to the side in an uncontrolled manner if the rotator cuff is disease or torn.

Question 19

Define the satellite cells of skeletal muscle

Answer 19

Satellite cells are located outside of the sarcolemma but within the basal lamina closely associated with a muscle fiber. It is a stem cell with the potential to differentiate into a myoblast. Function: post natal growth of muscle, repair + regeneration. Most abundant during growth and puberty, slowly decrease in number with age. Small amount remains in adulthood for repair. More concentrated in slow twitch muscle.

Question 20

Distinguish epimysium, perimysium, and endomysium

Answer 20

“Dense connective tissue sheaths.” Epimysium surrounds the whole muscle, perimysium surrounds fascicles, endomysium surrounds muscle fibers.

Question 21

Describe the dense bodies of smooth muscle fibers

Answer 21

Actin filaments bind dense bodies that are attached to the inner surface of the sarcolemma and throughout the sarcoplasm. Homologous to the Z- lines in skeletal muscle (aid in muscle contraction).

Question 22

Compile an overview of synchronous contraction of smooth muscle fibers

Answer 22

Variscosities (found along postsynaptic sympathetic nerve fibers) release norepinephrine that binds to the sarcolemma of smoothmuscle fibers. Gap junctions between muscle fibers allow rapid spread of norepinephrine induced action potential = synchronous muscle contraction. Myofilaments associate with actin (bound to dense bodies as an anchor) allow filament sliding for contraction of muscle.

Question 23

What is the cause of primary pulmonary hypertension?

Answer 23

Primary pulmonary arterial hypertension may be caused by thickening of the tunica media of artery vascular wall by hyperplasia and hypertrophy of smooth muscle cells by inhibition of cell apoptosis/loss of inhibition of proliferation in these cells.

Question 24

In the event of radial groove fracture in the humerus, why is forearm extension only weakened, not lost?

Answer 24

Forearm extension is controlled by the three heads of the triceps: the long, lateral, and medial head. All three of these are innervated by the radial nerve, which courses along the radial groove. The long and lateral heads are innervated superior to the radial groove, and the medial head is innervated in the radial groove. Thus, only medial head activity will be affected by fracture of the radial groove. Forearm extension can still occur by action of the lateral and long heads.

Question 25

Compare the embryonic origins of skeletal muscle and smooth muscle

Answer 25

Both are from the mesoderm.
Skeletal muscle comes from the somites, and some from the lateral plate’s parietal layer (such as the intrinsic shoulder muscles and upper limb muscles).
Smooth muscle comes from mesenchymal cells of the lateral plate’s visceral layer.

Question 26

Describe myofilaments, myofibrils, Z-lines, A bands, and I bands of skeletal muscle

Answer 26

Myofilaments: units of a muscle.
Myofibril: comprised of orderly-arranged myofilaments.

Sarcomeres make up myofilaments, and a sarcomere is comprised of Z-lines, A bands, and I bands.

A bands: anisotropic (no light) – dark, thick, myosin.
I bands: isotropic (light) – light, thin, actin.
Z-lines: Zwischenscheibe is German for “intermediate washers” - transverse. demarcate the boundaries of sarcomeres. Anchor the thin (actin, I) filaments.

Question 27

Describe role of triads during skeletal muscle contraction

Answer 27

Triads are crucial for excitation-contraction coupling.
Triads consist of 2 terminae cisternae (sarcoplasmic reticuli sacs) and one transverse tubule (an invagination of the sarcolemma).

I think that’s all we have to know, but fyi:
During contraction, the action potential received by the NMJ sarcolemma spreads along the transverse tubule network. When AP reaches t-tubule, opens calcium channels so that terminal cisternae (SR) calcium ions will enter t-tubules and proceed to bind on thin filaments, causing muscle contraction.

Question 28

Describe synapses between somatic motor axons and skeletal muscle fibers

Answer 28

Each skeletal muscle fiber joins with a somatic motor axon terminal, forming a neuromuscular junction. The action potential along the somatic motor axon stimulates release of acetylcholine from terminal buds. The acetylcholine binds at receptors in adjacent sarcolemma, stimulating an action potential along the membrane of the muscle fiber. This AP travels along the transverse tubule network, leading to muscle contraction.

Question 29

Compare type I, type IIA, and type IIB skeletal muscle fibers

Answer 29

Type I fibers:
highly fatigue-resistant. Low force activities like posture, walking.
slow-twitch. Dark or red. Profuse mitochondria.

Type II fibers:
fast-twitch. light or white. Small, sparse mitochondria.
IIA: moderately fatigue-resistant. Prolonged high force activities like marathon running.
IIB: minimally fatigue-resistant. Short, high-force activities like sprinting, power lifting.