MSK Histology

Question 1

Give three characteristics of a muscle cell (or fibre)

Answer 1

• striated
• unbranched
• multinucleate
  
  • nuclei are at periphery of the fibre but like not at the end like the periphery if you’re looking into the muscle fibres at a transverse cross-section
  • the nuclei sit just under the sarcolemma (the cell membrane)

Question 2

Give the special name for the muscle cell membrane

Answer 2

The sarcolemma

Question 3

Describe the relationship between muscles and fascicles

Answer 3

Muscle fibres are grouped into bundles called fascicles

A muscle typically contains several fascicles

Question 4

Name the three connective tissues seen in a muscle fibre

Answer 4

1. Epimysium
2. Perimysium
3. Endomysium

Question 5

Where are the three connective tissues in muscle fibres found?

Answer 5

1. Epimysium
   
   • the connective tissue that surrounds the muscle as a whole
2. Perimysium
   
   • the connective tissue around a single fascicle
3. Endomysium
   
   • the connective tissue around a single muscle fibre

EPE

Question 6

Define a sarcomere

Answer 6

The sarcomere extends from one Z line to the next

Question 7

Define a motor unit

Answer 7

A motor unit consists of one motor neurone and all of the muscle fibres that it innervates

Question 8

“An organ of fine control will have more muscle fibres per motor unit than an organ of power”

T/F?

Answer 8

False

The fewer the number of musle fibres in a motor unit, the finer the control of movement

Question 9

Name the three types of skeletal muscle fibre

Answer 9

Type I

Type IIA

Type IIB

Question 10

Describe skeletal muscle fibre Type I

Answer 10

• relatively slowly contracting fibres that depend on oxidative metabolism
• have abundant mitochondria and myoglobin
• resistant to fatigue
• produce relatively less force
• “red” fibres

Question 11

Describe skeletal muscle fibre Type IIA

Answer 11

• intermediate between Type I and Type IIB
• relatively fast contracting
• reasonably resistant to fatigue
• relatively uncommon

Question 12

Describe skeletal muscle fibre Type IIB

Answer 12

• fast contracting fibres
• depend on anaerobic metabolism
• few mitochondria
• less myoglobin than Type I fibres
• fatigue relatively easily
• produce relatively greater force
• “white” fibres

Question 13

Contrast cartilage and bone

Answer 13

Cartilage

• semi-rigid and deformable
• permeable
• avascular
• cells nourished by diffusion through the extracellular matrix

Bone

• rigid
• not permeable
• cells within the bone must be nourished by blood vessels that pervade the tissue

Question 14

What cells are found in cartilage? What is their name when immature?

Answer 14

Cells found in cartilage are called chondrocytes

Chondrocytes are called chondroblasts when immature

Question 15

Where are chondrocytes found (specifically)?

What is the role of chondrocytes?

Answer 15

Chondrocytes live within a space in the extracellular matrix termed a lacuna

Chondrocytes are active cells which not only secrete, but also maintain the extracellular matrix around them

Question 16

What are the three types of cartilage found in the body and which is most common?

Answer 16

• Hyaline (most common)
• Elastic cartilage
• Fibrocartilage

Question 17

What is hyaline cartilage made of?

Answer 17

1. 75% water
2. 25% organic material
   
   • 60% Type II collagen
   • 40% proteoglycan aggregates

Question 18

Briefly discuss the difference between Type I and Type II collagen

Answer 18

• Type II collagen is finer
• and instead of aggregating into linear bundles it forms a 3D meshwork

Type I collagen is most form found in most connective tissues e.g. tendon

Question 19

What are proteoglycan aggregates?

Answer 19

Proteoglycan aggregates are made up of GAGs (most commonly keratan sulfate and chondroitin sulfate) bound to a core protein and often linked to hyaluronan

Question 20

Describe hyaline cartilage

Answer 20

• grossly, blue & white in colour and translucent
• most common form of cartilage

Question 21

Describe elastic cartilage

Answer 21

• grossly it is light yellow in colour
• the addition of elastic fibres make it quite flexible

Question 22

Describe fibrocartilage

Answer 22

Hybrid between tendon and hyaline cartilage

• bands of densely packed type I collagen interleaved with rows of chondrocytes surrounded by small amounts of cartilagenous ECM
  
  • ECM= extracellular matrix
• grossly, it appears white

Question 23

Where can hyaline cartilage be found?

Answer 23

• articular surfaces
• tracheal rings
• costal cartilage
• epiphyseal growth plates
• precursor in fetus to many bones

Question 24

What is the function of bone?

Answer 24

To provide:

• Support
• Levers for effective movement
• Protection of internal organs (e.g. cranium, ribs)
• Calcium store
  
  • >95% of total calcium in the body is found in bone and there is constant exchange of calcium between bone and the blood
• Haemopoiessis (blood cell production)
  
  • in utero blood is produced in the liver and spleen
  • BUT well before birth it begins in the bone marrow
  • by birth bone marrow is the site of haemopoiesis
  • by early 20s typically only the axial and limb girdle skeleton is involved in blood production

Question 25

What is the composition of bone?

Answer 25

1. 65% bioapatitie (a form of calcium phosphate, mostly hydroxyapatite) 2. 23% collagen 3. 10% water 4. 2% non-collagen proteins

Question 26

Is cortical bone found at the epiphyses?

Answer 26

Nope don't think so

Question 27

What are the living cells that make bone called?

Answer 27

Osteocytes

Question 28

How can you tell this osteon has formed during remodelling and not in original development?

Answer 28

The lines that are often visible surrounding the osteon are termed cement lines and are only found in osteons that have formed during remodelling

Question 29

Does trabecular bone have as many Haversian canals as cortical bone? Why?

Answer 29

* Trabecular bone generally lacks Haversian canals because the struts are think so osteocytes can survive from contact with the marrow spaces

Question 30

Name the cells of the bone

Answer 30

1. Osteoprogenitor cells 2. Osteoblasts 3. Osteocytes 4. Osteoclasts

Question 31

What is the role of osteoprogenitor cells?

Answer 31

Osteoprogenitor cells are located on bone surfaces e.g. under the periosteum Osteoprogenitor cells serve as a pool of reserve osteoblasts

Question 32

What is the role of osteoblasts?

Answer 32

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

Question 33

What are the role of osteocytes?

Answer 33

An osteocyte is a bone cell trapped within the bone matrix

Question 34

What is the role of osteoclasts?

Answer 34

Osteoclasts are large multinucleated cells They are found on the surface of bone and are responsible for bone resorption

Question 35

Describe bone remodelling

Answer 35

Bone is constantly undergoing remodelling 1. a number of osteoclasts will congregate and begin to "srill" into the bone, forming a tunnel 2. a blood vessel will grow into the tunnel 3. bringing with it osteoblasts which line the tunnel 4. osteoblasts begin laying laying down new lamerllar bone 5. this process continues until only the space of Haversian canal remains

Question 36

What is the basic multicellular unit/BMU?

Answer 36

The collection of osteoclasts and osteoblasts that participate in this process at a site is called the BMU

Question 37

What do osteoblasts secrete? (think about what you know about osteoblasts role and about the makeup of bone)

Answer 37

Osteoblasts secrete: * collagen, * glycosaminoglycans (GAGs), * proteoglycans * and other organic components of the matrix which is collectively termed osteoid. This then becomes mineralised over time in the extracellular space.

Question 38

What is the mineral of bone principally made up of?

Answer 38

Calcium phosphate crystals, particularly hydroxyapatite

Question 39

What do we belive the lineage of osteoclasts to be?

Answer 39

It is thought that osteoclasts are derived from macrophage lineage of cells Several of these cells will fuse and form a single giant cell

Question 40

During bone remodelling, where can a) osteocytes b) osteoblasts be found?

Answer 40

Osteoblasts are actively secreting matrix that will become bone. Note that because bone is a solid matrix, it can only be added at a surface.

Question 41

What are the important differences between lamellar and woven bone?

Answer 41

During development/following a break, the bone laid down differs from normal lamellar bone, because rather than having collagen fibres orientated all in one direction the collagen fibres are laid down in a haphazard fashion Woven bone is not as strong as lamellar bone and is subsequently remodelled into lamellar bone by being broken down by osteoclasts and reformed by new osteoblasts.