Musculoskeletal Histology

Question 1

3 types of muscle?

Answer 1

Skeletal (voluntary)
Cardiac
Smooth

Question 2

3 features of skeletal muscle cells/fibres?

Answer 2

Striated

Unbranched

Multi-nucleate (forming a synctium) - nuclei are at the fibre periphery, under the membrane (called the sarcolemma)

Question 3

How are muscle fibres grouped?

Answer 3

Into bundles called FASCICLES

Question 4

Connective tissue in skeletal muscles?

Answer 4

If it surrounds the muscle as a whole - epimysium

Around a single fascicle - perimysium

Around a single muscle fibre - endomysium

Question 5

What are sarcomeres?

Answer 5

Smallest functional contractile elements; these group together to form myofibrils which, in turn, group to form the muscle fibre

Question 6

…………………

Answer 6

………………….

Question 7

…………………..

Answer 7

……………………

Question 8

Why are skeletal muscle fibres striated?

Answer 8

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

Z-lines in the sarcomere of one myofibril will be aligned with the Z-lines of the sarcomeres in other myofibrils, so it looks like something is running across the fibre

Question 9

What is a motor unit?

Answer 9

An α-motor neurone and all of the muscle fibres that it innervates

Question 10

How do muscle fibres in a motor unit vary?

Answer 10

The number of fibres can vary; fewer the no. of muscle fibres in a motor unit, the finer the control of movement

However, the fibres are all of the same type and are scattered in the muscle

Question 11

Junction between the motor neuron and skeletal muscle?

Answer 11

Axon of the motor neuron branches as it nears its termination

Each branch ends in a NEUROMUSCULAR JUNCTION

Question 12

3 types of skeletal muscle fibres?

Answer 12

Type I - relatively slowly contracting fibres that depend on oxidative metabolism

Type IIa (uncommon) - intermediate between the other two; relatively fast contracting but also reasonably resistant to fatigue

Type IIb (AKA white fibres) -fast-contracting fibres that depend upon anaerobic metabolism; few mitochondria, fatigue easily and produce relatively great force

Question 13

Compare cartilage and bone?

Answer 13

Cartilage is semi-rigid and deformable, avascular and cell nourished by diffusion through the EC matrix

Bone is rigid and not permeable; cells within the bone must be nourished by blood vessels that pervade the tissue

Question 14

Cartilage cells?

Answer 14

Chondrocytes - within the lacuna (space in the EC matrix); they are active cells which secrete and maintain the EC matrix

They are called chrondroblasts when immature

Question 15

Components of the ECM in hyaline cartilage (most common)?

Answer 15

1. 75% water
2. 25% organic material:
   • 60% type II collagen
   • 40% proteoglycan aggregates (made up of GAGs) bound to a core protein and often linked to hyaluronan

Question 16

Differences between type I and II collagen?

Answer 16

Type I is the most common form of collagen and aggregates into linear bundles

Type II is finer and forms a 3D network

Question 17

Types of cartilage?

Answer 17

Hyaline cartilage (most common) - grossly, blue-white in colour and transclucent

Elastic cartilage - grossly, light yellow in colour; elastic fibres make it flexible

Fibrocartilage - grossly, appears white and is a hybrid of tendon and hyaline cartilage
Bands of densely packed type I collagen inter-weaved with rows of chondrocytes are surrounded cartilagenous ECM

Question 18

Examples of sites where hyaline cartilage is found?

Answer 18

Articular surfaces

Tracheal rings

Costal cartilage

Epiphyseal growth plates

In fetus, precursor to many bones

Question 19

………………

Answer 19

……………….PINK PICTURE

Question 20

Functions of bone?

Answer 20

• Support
• Levers for effective movement
• Protection of internal organs
• Ca2+ store
• Haemopoiesis

Question 21

Describe haemopoiesis

Answer 21

Blood cell production

• While in utero, blood is produced in the liver and spleen but it begins in the bone marrow before birth
• By time of birth, bone marrow is the site of haemopoiesis
• By early 20s, only the axial and limb girdle skeleton is involved in blood production

Question 22

Composition of bone?

Answer 22

Collagen, minerals, water and non-collagen proteins

Question 23

Morphology of bone?

Answer 23

Outer shell of dense cortical bone makes up the diaphysis

Cancellous/trabecular bone occupies the epiphyses (looks like inside of an aero bar)

Question 24

One similarity and one difference between compact and trabecular bone?

Answer 24

Both are lamellar (made up of layers)

Adjacent to trabecular bone, there are marrow cavities (spaces)

Question 25

Bone as a living tissue?

Answer 25

Penetrated by small canals for blood vessels and nerves

Contains osteocytes (living cells)

Question 26

Morphology of cortical bone?

Answer 26

Cross-sectioning shows OSTEONS (look like “tree rings”)

These consist of concentric lamellae around a Haversian canal, which contains nerves and blood vessels that serve the bone

Question 27

Difference between Haversian canal and Volkmann’s canal?

Answer 27

Haversian canal is the axis of the osteon and is longitudinal

Volkmann’s canal has a transverse orientation and interconnects Haversian canals

Question 28

What are cement lines?

Answer 28

Lines that are often visible surrounding the osteon; only found in osteons that have formed during REMODELLING, not in original development

Question 29

Describe the structure of trabecular bone

Answer 29

AKA spongy bone

Has osteocytes but lacks Haversian canals; osteocytes can survive from contact with the marrow spaces

Question 30

4 types of cells of bone, their location and functions?

Answer 30

Osteoprogenitor cells - located on bone surfaces, e.g: under the periosteum; they form a pool of reserve osteoblasts

Osteoblasts - bone-forming cells found on the surface of developing bone; have plentiful RER and prominent mitochondria

Osteocytes - bone cell trapped within bone matrix

Osteoclasts - large multi-nucleated cells found on the surface of bone and responsible for bone resorption

Question 31

Describe remodelling of bone

Answer 31

Osteoclasts congregate and begin to ‘drill’ into the bone, forming a tunnel through which a blood vessel will grow

This brings osteoblasts which line the tunnel and begin laying down new lamellar bone; continues until only the space of a Haversian canal remains

Question 32

What is the basic multicellular unit (BMU)?

Answer 32

Collection of osteoclasts and osteoblasts that participate in bone remodelling

Question 33

How does bone mineralisation occur?

Answer 33

Osteoblasts secrete collagen, GAGs, proteoglycans and other organic components of the matrix (together, these are called the OSTEOID)

It becomes mineralised over time in the EC space

Question 34

What does bone mineral consist of?

Answer 34

Principally, calcium phosphate crystals, part. hydroxyapatite

Question 35

Formation of osteoclasts?

Answer 35

Derived from macrophage lineage; several will fuse to form a single GIANT CELL

Question 36

Difference between the function of osteoclasts and osteoblasts?

Answer 36

Osteoclasts - destroy bone

Osteoblasts - secrete matrix that will become bone

Question 37

Consequences of remodelling bone?

Answer 37

Younger osteons often partially obliterate older osteons

Question 38

When can woven bone be seen?

Answer 38

During development

Following a fracture

Question 39

Compare lamellar and woven bone

Answer 39

Woven bone:
• Collagen fibres are laid down haphazardly
• Not as strong as lamellar bone
• Is subsequently remodelled into lamellar bone as it is broken down by osteoclasts and reformed by osteoblasts

Lamellar bone:
• Collagen fibres are orientated in one direction