MSK: Histology

Question 1

What cells in the embryo fuse together to form multi-celled muscle fibre/syncytiums?

Answer 1

Myoblasts.

Question 2

What is a muscle fibre composed of?

Answer 2

Cytoplasm filled with myofibrils.

Question 3

What is a fascicle composed of?

Answer 3

Muscle fibres clumped together.

Question 4

What is a muscle composed of?

Answer 4

Multiple fascicles held together by connective tissue (endomycium, perimycium, and epimycium).

Question 5

Individual muscle fibres are multinucleated because they are made of multiple myoblasts fused together. Roughly how many myoblasts in the embryo fuse together to form a single muscle fibre (syncytium)?

Answer 5

Hundreds.

Question 6

What is a sarcolemma?

Answer 6

Cell membrane of skeletal muscle cell.

Question 7

What is a sarcoplasmic reticulum?

Answer 7

Endoplasmic reticulum of a skeletal muscle cell.

Question 8

What is sarcoplasm?

Answer 8

Cytoplasm of a skeletal muscle cell.

Question 9

If looking for striated cytoplasm of skeletal muscle histologically, should you use a longitudinal or transverse section?

Answer 9

Longitudinal.

Question 10

Why is striated muscle striated?

Answer 10

Myofibrils are in register (sarcomeres are lined up).
Actin rich parts of sarcomere appear as light bands. Myosin rich parts of sarcomere appear as dark bands (‘A bands’).

Question 11

Histochemical stains looking for ATPase can be used to see what two different muscle fibres, that cannot be distinguished with H&E stain?

Answer 11

Type 1 (rich in ATPase, use oxidative phosphorylation, fatigue resistance “slow twitch”)
Type 2 (muscles that give short bursts of power, “fast twitch”)

Question 12

Muscle fibres can be categorised into type 1 “slow twitch” and type 2 “fast twitch”.
How are type 2 muscle fibres further subdivided?

Answer 12

Fatigue resistance (derive their energy from oxidative and glycolytic metabolism).
Fatigue sensitive (derive their energy only from glycolysis).

Question 13

Describe a muscle spindle.

Answer 13

Intrafusal muscle fibres wrapped around a nerve fibre. Contained within a fibrocollagenous capsule.
(Look like an eye).

Question 14

What specialised organ lies between muscle fibres within a fascicle, and detects stretch and tension within a muscle?

Answer 14

Muscle spindle.

Question 15

What are the three types of connective tissue in muscle, and where are they?

Answer 15

Endomysium = in between individual muscle fibres.
Perimysium = binds together muscle fibres to form fascicles.
Epimysium = binds fascicles together to form muscle.

Question 16

What are Sharpey’s fibres composed of?

Answer 16

Bundles of collagen.

Question 16

What is the function of Sharpey’s fibres?

Answer 16

Sharpey’s fibres connect epimysium, on the outside of muscle, to collagen that makes up bone.

Question 17

What are tendons composed of?

Answer 17

Parallel bundles of collagen with intervening fibroblasts.

Question 18

When are tendons used over Sharpey’s fibres?

Answer 18

Sharpey’s fibres are for connecting muscle over a wide area to bone e.g. rotator cuff muscles to the scapula.
Tendons are for connecting muscles over a small area e.g. rotator cuff muscles to the humerus.

Question 19

What is osteoid, and what does it contain?

Answer 19

Unmineralised bone.
Extracellular matrix produced by osteoblasts, containing type 1 collagen, glycosaminoglycans, and proteoglycans.

Question 20

What cells do osteoblasts develop from?

Answer 20

Osteoprogenitor cells.

Question 21

How are osteocytes connected to neighbouring cells?

Answer 21

Via canaliculi.

Question 22

What is the term for the depressions in bone created by osteoclasts?

Answer 22

Howship’s lacunae.

Question 23

Why is the glycosaminoglycan component of osteoid important for forming mineralised bone?

Answer 23

Glycosaminoglycans include compounds such as osteocalcin, which have a strong affinity for calcium ions.

Question 24

Osteoid can be deposited by osteoblasts in parallel sheets or haphazardly. Which structure forms lamellar bone, and which forms woven bone?

Answer 24

Parallel sheets = lamellar bone. Haphazardly = woven bone.

Question 25

What is the faint blue line between osteoid and bone seen histologically?

Answer 25

The cement line.

Question 26

What microscopic round structures of concentric rings of bone are found in lamellar bone?

Answer 26

Osteons.

Question 27

Lamellar bone is formed of round osteons. What is found in the centre of osteons?

Answer 27

Haversian canal, containing blood vessel.

Question 28

What are the four layers in the process of endochondrial ossification?

Answer 28

Resting cartilage (chondrocytes). Zone of hyperplasia (columns of new chondrocytes) Zone of hypertrophy (new chondrocytes enlarge, erode extracellular matrix) Zone of ossification (remaining matrix becomes calcified, osteoblasts start remodelling).

Question 29

Synovium lines the inside of the joint capsule. What is synovial formed of?

Answer 29

1-4 layers of synovial cells.

Question 30

Synovial cells can be variable shapes including squamous or cuboidal, but there are only two key types of synovial cells. What are the two types of specialised synovial cells?

Answer 30

Type A - phagocytes Type B - rich in rER, secrete synovial fluid

Question 31

Synovium is specialised tissue lining the inner surface of the joint capsule. What is the level of vasculature and innervation of synovium?

Answer 31

Synovium, unlike hyaline cartilage, is richly vascular and highly innervated.