Lecture 13 - Joints, Tendon and Skeletal muscle

Question 1

What are fibrous joints?

Answer 1

They are dense fibrous connective tissue that unites 2 bones e.g. skull sutures, tibio-fibular joint. Results in very restricted movement.

Question 2

What are cartilage joints?

Answer 2

Cartilage joints are solid cartilage between 2 bones. (1st rib and manubrium) Virtually don’t allow any movement.

Question 3

What forces can fibrocartilage resist? and where are some examples of these joints

Answer 3

Fibrocartilage provides cushioning, but also provides tensile strength and they resist shearing

Question 4

Describe the composition of fibrocartilage

Answer 4

It’s dense regular connective tissue with hyaline cartilage. It has chondrocytes in rows, and type l and ll collagen. There is NO perichondrium, only connective tissue and fibroblasts (this is why recovery is limited in this area)

Question 5

What function does synovial fluid have?

Answer 5

Acts as a shock absorber and a lubricant, and as provides nutrition to chondrocytes.

Question 6

What is present in synovial fluid?

Answer 6

Glycoprotein, lubricin (lubricates cartilage)

Synovial fluid secretion occurs due to mechanical stimulation

Question 7

What are the cells lining the synovial membrane known as? And what kind of tissues and structures are found in this layer

Answer 7

This is the subintimal layer. The lining cells are fibroblast and macrophage like, but they are NOT epithelial cells. In the subintimal layer there is adipose and fibrous tissue, and there are also blood vessels and nerves

Question 8

What are ligaments main function?

Answer 8

To hold bones together, keeping them aligned. Misalignment can lead to bone damage.

Question 9

What are the functions of ligaments?

Answer 9

Ligaments hold the skeleton together. They provide some flexibility, and give high tensile strength. They also transmit load from bone to bone, and they provide stability at joints to maintain joint congruency.

Question 10

What are the functions of tendons?

Answer 10

It is connective tissue specialised to: Harness contractile force and transmits it in one axis if possible

Question 11

Describe the arrangement of tendons

Answer 11

Tendons are dense regular connective tissue. They contain densely packed fibres which have a parallel array, and are packaged into fascicles. This tissue is relatively avascular and is slow to heal. Between fascicles lies dense irregular FCT, nerves and blood vessels

Question 12

What are the two junctions of tendons?

Answer 12

the proximal myotendinous junction, and the distal osteotendinous junction

Question 13

Describe the composition of a tendon

Answer 13

85% of tendon mass are Collagen type l & ll fibers There are flattened fibroblasts between the layers of parallel fibres (tenocytes). The tenocytes have extended cytoplasmic processes that allows contact with neighbouring cells

Question 14

How are tendons joined to muscle at the myotendinous junction?

Answer 14

Via actin filaments which connect the muscle to the tendon ECM. This is bound together by a-actinin or desmin.

Question 15

What are the connective tissue components of skeletal muscle? and what is the function of these compartments?

Answer 15

Outermost, there is the epimysium, whic is dense CT fascia sheath arond anatomical muscle

Then there’s the perimysium, which surrounds each fascile

And then the endomysium, which is between each individual muscle cell

The connective tissue components of skeletal muscle acts to harness the contraction, and to exert it onto the tendon for movement.

They also act as conduits for nerve and blood vessels

Question 16

Describe a myocyte

Answer 16

They are large, multinucleate cells. The nuclei lie at the periphery, and the cell has distinct striations.

The striations are caused by the arrangement of actin and myosin.

Question 17

Describe myogenesis

Answer 17

Myoblasts form myocytes in a process called myogenesis.

Myoblasts that do not produce myocytes form myosatellite cells, which remain adjacent to the myocyte between the sarcolemma and basement membrane.

When stimulated, these satellite cells can differentiate into myocytes

Question 18

What are the I and A bands of sarcomeres

Answer 18

I bands are where thin filaments are located

A bands have thick filaments

Question 19

How are sarcomeres joint to together, and how can this been seen on a microscope?

Also, describe changes seen in the A and I band during contraction.

Answer 19

They are joined by Z lines, which are seen as dark lines between sarcomeres. The actin within each sarcomere binds to the Z line as an achoring point

During contraction, the A band remains constant, but the I band changes.

Question 20

What protein connects actin to the Z line?

Answer 20

Alpha-actinin

Question 21

How does myofilament movement generate muscle movement?

Answer 21

The myofilaments are anchored within the cell by dystrophin.

Dystrophin is a cytoplasmic protein, and a vital part of a protein complex that connects the cytoskeleton of a muscle fiber to the surrounding extracellular matrix through the cell membrane.

So when contraction occurs, this is transmitted to the ECM (laminin 2), which is then transmitted to connective tissue for movement.

The absence of dystrophin results in progressive muscle weakness (Duchenne’s muscular dystrophy)