Bone Structure and Core MSK Histology

Question 1

How does skeletal muscle appear?

Answer 1

Cells are striated, unbranched and multinucleate (forms a syncytium)

Question 2

What shape are skeletal muscle fibres and how are they grouped?

Answer 2

Fibres are long cylinders 10-100 micrometers in diameter and 1000-200000 micrometers in length; grouped into bundles called fascicles (each muscle contains several fascicles)

Question 3

Where are the nuclei of skeletal muscle cells located?

Answer 3

At the periphery of the fibre, just under the cell membrane (called the sarcolemma in muscle cells)

Question 4

What is the epimysium?

Answer 4

Connective tissue that surrounds the muscle as a whole

Question 5

What is the perimysium?

Answer 5

Connective tissue that surrounds a single fasicle

Question 6

What is the endomysium?

Answer 6

Connective tissue that surrounds a single muscle fibre

Question 7

How is muscle organised?

Answer 7

Each muscle fibre contains many myofibrils, with each myofibril consisting of many sarcomeres placed end to end

Question 8

What are sarcomeres?

Answer 8

Unit of contraction of muscle cell, smallest contractile elements in the straited muscle cell

Question 9

Where do sarcomeres extend to?

Answer 9

From one Z-line to the next

Question 10

Why do striated fibres have a regular pattern of bands running across the fibres?

Answer 10

Sarcomeres in the myofibrils have alternating light and dark bands, and are held in registry with one another across the fibre

Question 11

How are striations organised in a fibre?

Answer 11

They run across the fibre at right angles to the long axis

Question 12

How do sarcomeres align with each other in a fibre?

Answer 12

The Z-disks in the sarcomere in one myofibril will be aligned with the Z-disks of the sarcomeres in the surrounding myofibrils

Question 13

What does the motor unit of a skeletal muscle consist of?

Answer 13

One motor neuron and all of the muscle fibres that it innervates

Question 14

What does having fewer muscle fibres attached to a motor neuron allow?

Answer 14

Finer control of movement

Question 15

What is the neuromuscular junction?

Answer 15

Special type of synapse at the end of each branch of the motor neuron axon

Question 16

How are the fibres of each motor unit organised in the skeletal muscle?

Answer 16

Scattered throughout the muscle and are all the same fibre type

Question 17

What is type I skeletal muscle?

Answer 17

Relatively slow contracting fibres that depend on oxidative metabolism, abundant mitochondria and myoglobin, resistant to fatigue, produce less force, often called “red fibres”

Question 18

What is type IIa skeletal muscle?

Answer 18

Relatively fast contracting but also reasonably resistant to fatigue, relatively uncommon

Question 19

What is type IIb skeletal muscle?

Answer 19

Fast contracting fibres that depend on anaerobic metabolism, few mitochondria and less myoglobin, fatigue relatively easily, produce relatively greater force, often called “white fibres”

Question 20

What are some features of cartilage?

Answer 20

Semi-rigid, deformable, permeable, avascular, cells nourished by diffusion through the extracellular matrix

Question 21

What are some features of bone?

Answer 21

Rigid, not permeable, cells within the bone must be nourished by blood vessels that pervade the tissue

Question 22

What are chondrocytes?

Answer 22

Cells found in cartilage (chondroblasts when immature), active cells that both secrete and maintain the extracellular matrix around them

Question 23

Where are chondrocytes located in cartilage?

Answer 23

Live within a space in the extracellular matrix termed the lucuna

Question 24

What is the confirmation of the extracellular matrix in hyaline cartilage?

Answer 24

75% water, 25% organic material

Question 25

What is the organic material that makes up the extracellular matrix?

Answer 25

60% type II collagen = finer (15-45 micrometers), forms 3D network 40% proteoglycan aggregates = made up of GAGs (most commonly keratin sulphate and chondroitin suphate) bound to a core protein and often linked to hyaluronan

Question 26

What are the types of cartilage?

Answer 26

Hyaline, elastic, fibrocartilage

Question 27

What are some features of hyaline cartilage?

Answer 27

Most common form, found at articular surfaces, tracheal rings, costal cartilage, epiphyseal growth plates and in fetus as precursor to many bones, blue-white and translucent

Question 28

What are some features of elastic cartilage?

Answer 28

Light yellow, addition of elastic fibres make it quite flexible

Question 29

What are some features of fibrocartilage?

Answer 29

Hybrid between tendon and hyaline cartilage, bands of densely packed type I collagen interleaved with rows of chondrocytes surrounded by small amounts of cartilaginous ECM, appears white

Question 30

What are some function of bone?

Answer 30

Support and lever for movement, protects internal organs, calcium store, haemopoiesis

Question 31

How does bone act as a calcium store?

Answer 31

More than 95% of the total calcium in the body is stored in the bones and there is constant exchange of calcium between bone and the blood

Question 32

Where does haemopoiesis begin, and where are the main sites in adults?

Answer 32

Begins in bone marrow before birth; by early twenties typically only the axial and limb girdle skeleton is involved in blood production

Question 33

What is the composition of bone?

Answer 33

23% collagen, 65% bioapatite (form of calcium phosphate, mostly hydroxyapatite), 10% water, 2% non-collagen proteins

Question 34

What kind of bone makes up the outer shell (diaphysis)?

Answer 34

Dense cortical bone

Question 35

What kind of bone makes up the ends of the bones (epiphyses)?

Answer 35

Cancellous/trabecular bone (fine meshwork)

Question 36

When does bone undergo remodelling?

Answer 36

Throughout life

Question 37

What are some similarities between compact and trabecular bone?

Answer 37

Similar bone cells and matrix, both lamellar (made of layers)

Question 38

Where are the marrow cavities in relation to trabecular bone?

Answer 38

Adjacent to the bone

Question 39

How do blood vessels and nerves penetrate the bone?

Answer 39

Through small canals

Question 40

What are the living cells found in bone called?

Answer 40

Osteocytes

Question 41

What are cement lines?

Answer 41

Visible lines around osteons that have formed during remodelling

Question 42

Does trabecular bone have Haversian canals?

Answer 42

No = struts are thin so osteocytes survive from contact with marrow spaces

Question 43

What are the different types of bone cells?

Answer 43

Osteoprogenitor cells, osteoblasts, osteocytes, osteoclasts

Question 44

What are osteoprogenitor cells?

Answer 44

Serve as pool of reserve osteocytes, found on bone surfaces

Question 45

What are osteoblasts?

Answer 45

Bone forming cells found on the surface of developing bone, have plentiful RER and prominent mitochondria

Question 46

Where are osteocytes located?

Answer 46

Trapped within the bone matrix

Question 47

What are osteoclasts?

Answer 47

Large (>40 micrometers) multinucleated cells, found on bone surface and are responsible for bone resorption, several cells fuse to form single giant cell, thought to be derived from macrophage lineage

Question 48

How does bone remodelling begin?

Answer 48

Number of osteoclasts will congregate and begin to "drill" into the bone forming a tunnel

Question 49

How are blood vessels involved in bone remodelling?

Answer 49

Blood vessels grow into the tunnel created by osteoclasts, bringing with them osteoblasts which then line the tunnel and begin laying down new lamellar bone

Question 50

When does bone remodelling stop?

Answer 50

Until only the space of a Haversian canal remains

Question 51

What is osteoid?

Answer 51

The collagen, glycosaminoglycans (GAGs), proteoglycans and other organic compounds secreted by osteoblasts

Question 52

What happens to osteoid over time?

Answer 52

It becomes mineralised in the extracellular space

Question 53

What is the main mineral of bone?

Answer 53

Calcium phosphate crystals, particularly hydroxyapatite (Ca10(PO4)6(OH)2)

Question 54

How does woven bone differ from normal lamellar bone?

Answer 54

Collagen fibres are orientated haphazardly, isn't as strong as lamellar bone, and is subsequently remodelled into lamellar bone by being broken down by osteoclasts and reformed by new osteoclasts

Question 55

When is woven bone laid down?

Answer 55

During development of after a bone is broken