Bone structure and core MSK histology

Question 1

what are the 3 types of muscle

Answer 1

skeletal or voluntary

cardiac

smooth

Question 2

describe skeletal muscle cells

Answer 2

striated

unbranched

multinucleated (forms syncytium)

Nuclei are at the periphery of the fibre, just under the cell membrane (in muscle cells is called the sarcolemma)

Question 3

how are skeletal muscle fibres grouped ?

Answer 3

Into bundles called fascicles. A muscle typically contains several.

Question 5

what is the connective tissue which surrounds the skeletal muscle as a whole called?

Answer 5

epimysium

Question 6

what is the connective tissue which surrounds a single fascile called ?

Answer 6

perimysium

Question 7

what is the connective tissue which surrounds a single muscle fibre called ?

Answer 7

endomysium

Question 8

what is this microscope pic of?

Answer 8

striated skeletal muscle

Question 9

what is the smallest contractile elements in skeletal muscles ‘known as unit of contraction’ called?

Answer 9

sarcomeres

Question 10

what do sarcomeres form when placed end to end ?

Answer 10

myofibrils

Question 11

how are myofibrils packed together?

Answer 11

packed together like cigarettes in a pack - in the muscle fibres

Question 12

what is an unusual feature about skeletal muscles ?

Answer 12

they have mutli nuclei

Question 13

what does a motor unit consist of ?

Answer 13

One motor neurone and all of the muscle fibres that it innervates (anywhere from a few to more than a hundred fibres).

Question 14

The axon of the motor neurone branches as it nears its termination and each branch ends in a special type of synapse - what is this synapse called ?

Answer 14

neuromuscular junction

Question 15

the fewer the numebr of muscle fibres in a motor unit the finer the control of movement (T/F)

Answer 15

true

Question 16

what are the 3 types of skeletal muscle ?

Answer 16

Type I

Type IIA

Type IIB

Question 17

describe type I skeletal muscle

Answer 17

Relatively slowly contracting fibres that depend on oxidative metabolism. They have abundant mitochondria, are resistant to fatigue and produce relatively less force. Often called ‘red’ fibres.

Question 18

describe type IIA muscle fibres

Answer 18

They are relatively fast contracting, but are also reasonably resistant to fatigue. These fibres are relatively uncommon.

Question 19

describe type IIB muscle fibres

Answer 19

Fast contracting fibres that depend on anaerobic metabolism. They have few mitochondria, fatigue relatively easily and produce relatively greater force. Often called ‘white’ fibres.

Question 20

describe cartilage in general terms

Answer 20

Semi-rigid and Deformable

Permeable

Avascular

Cells nourished by diffusion through the extracellular matrix.

Question 21

describe bone in general terms

Answer 21

Rigid

Not Permeable

Cells within the bone must be nourished by blood vessels that pervade the tissue.

Question 22

what are the cells found within cartilage ?

Answer 22

chondrocytes (chondroblasts when immature)

Question 23

what is the function of chondrocytes and where are they situated within cartilage

Answer 23

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 24

what is the extracellular matrix (ECM) in cartilage comprised of ?

Answer 24

75% water

25% organic material of which - 60% is type II collagen and 40% is proteoglycan aggregates made up of GAG’s - (side note)(most commonly keratan sulfate and chondroitin sulfate) bound to a core protein and often linked to hyaluronan.

Question 25

what are the 3 different types of cartilage

Answer 25

hyaline, elastic and fibrocartliage

Question 26

describe hyaline cartilage

Answer 26

it is blue-white in colour and translucent. most common form of cartilage

Question 27

describe elastic cartilage

Answer 27

light yellow in colour, addition of elastic fibres makes it quite flexible

Question 28

describe fibrocartliage

Answer 28

Hybrid between tendon and hyaline cartilage. It has bands of densely packed type I collagen interleaved with rows of chondrocytes surrounded by small amounts of cartilagenous ECM. Grossly, fibrocartilage appears white.

Question 29

give some examples of where hyaline cartilage is found

Answer 29

Articular surfaces

Tracheal rings

Costal cartilage

Epiphyseal growth plates

Precursor in fetus to many bones

Question 30

identify the letters for the synovial joint in the finger

Answer 30

Note that the gap between the articular cartilages (‘C’) is artifactual. ‘CP’ is the joint capsule, ‘S’ the synovial membrane, and ‘E’ the tendon of the extensor muscle.

Question 31

what are the functions of bone

Answer 31

Support

Levers for effective movement.

Protection of internal organs (e.g. cranium, ribs)

Calcium store

Haemopoiesis (blood cell production)

Question 32

what is the composition of bone?

Answer 32

Question 33

describe the outershell of bone i.e. what makes up the shaft and ends of the bone

Answer 33

An outer shell of dense cortical bone makes up the shaft (diaphysis).

Cancellous or trabecular bone occupies the ends of the bone (the epiphyses). Cancellous bone is a fine meshwork of bone that looks a bit like the inside of an Aero bar.

Question 34

describe the differences between compact and trabecular bone

Answer 34

Main difference is the presence of spaces (marrow cavities) adjacent to trabecular bone.

Question 35

what are the living cells called that bone contains ?

Answer 35

osteocytes

Question 36

how does bone gets its blood supply ?

Answer 36

it is penetratedby small canals for the blood vessels

Question 37

label the features

Answer 37

Question 38

describe what cement lines are - found in bone

Answer 38

Often visible surrounding the osteon are termed cement lines. These are only found in osteons that have formed during remodelling.

Question 39

describe trabecular bone

Answer 39

Trabecular bone has osteocytes and is lamellar in nature, but generally lacks Haversian canals. Because the struts are thin, the osteocytes can survive from contact with the marrow spaces.

Note the pink spaces are bone marrow spaces

Question 40

describe osteoprogenitor cells ?

Answer 40

located on bone surfaces, for example under the periosteum, these cells serve as a pool of reserve osteoblasts

Question 41

what are osteoblasts ?

Answer 41

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

Question 42

what are osteocytes ?

Answer 42

a bone cell trapped within the bone matrix.

Question 43

what are osteoclasts and what are they responsible for ?

Answer 43

Large multinucleated cells. They are found on the surface of bone and are responsible for bone resorption. (reabsorbed)

Question 44

describe the basics of bone remopdelling

Answer 44

In this process, a number of osteoclasts will congregate and begin to ‘drill’ into the bone, forming a tunnel. A blood vessel will grow into the tunnel bringing with it osteoblasts which line the tunnel and begin laying down new lamellar bone.

prcoess continues until only a haversion canal remains

Question 45

what is the collection of osteoblasts and osteoclasts that participate in bone remodelling called?

Answer 45

the basic multicellular unit (BMU)

Question 46

what is the collective term for what osteoblasts secrete called ? and also give a few examples of some of the organis materials it is comprised of

Answer 46

it is called osteoid, contains e.g. collagen, glycosaminoglycans (GAGs) etc

Question 47

during a brake how does the bone laid down differ from normal lamellar bone?

Answer 47

Because rather than having collagen fibres orientated all in one direction, as occurs in lamellar bone, the collagen fibres are laid down in a haphazard fasion. This type of bone is called woven bone. Woven bone is not as strong and is subsequently remodelled into lamellar bone by being broken down by osteoclasts and reformed by new osteoblasts.