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MSK > Histology > Flashcards

Histology Flashcards

1
Q

Name the three principle types of muscle

A
  • skeletal or voluntary
  • cardiac
  • smooth
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2
Q

What is the sarcolemma?

A

Plasma membrane of a muscle cell

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3
Q

Where are the nuclei found in skeletal muscle fibres?

A

At the periphery of the fibre, just under the cell membrane (sarcolemma)

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4
Q

Muscle fibres are grouped into bundles called what?

A

Fascicles

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5
Q

What is the epimysium?

A

The connective tissue that surrounds the muscle as a whole, outer layer

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6
Q

Each fascicle is made up of what?

A

Packed muscle cells

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7
Q

What is the perimysium?

A

The connective tissue around a single fascicle

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8
Q

What is the endomysium?

A

The connective tissue around a single muscle fibre. Wispy connective tissue

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9
Q

Each muscle fibre contains many what?

A

Myofibrils

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10
Q

Each myofibril consists of what?

A

Many sarcomeres placed end to end

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11
Q

What is the unit of contraction within muscles?

A

Sarcomeres

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12
Q

By definition, the sarcomere extends from where?

A

From one Z line to the next

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13
Q

What is the I band?

A

Actin thin filaments anchored to a central line (z line)

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14
Q

Why are skeletal muscle fibres striated?

A
  • viewed under the microscope the fibres have a regular pattern of bands running across the fibre at right angles to the long axis
  • this is also true for cardiac muscle
  • this is because the sarcomeres in the myofibrils with their alternating dark and light bands are held in registry with one another
  • that is, the z disks in the sarcomere of one myofibril will be aligned with the z disks of the sarcomeres in the surrounding myofibrils
  • although nothing is physically running across the fibre, it looks as though it is
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15
Q

What is a motor unit?

A

A motor unit consists of one motor neurone and all of the muscle fibres that it innervates (anywhere from a few to more than a hundred fibres)

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16
Q

The fewer the number of muscle fibres in a motor unit …..

A

The finer the control of the movement

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17
Q

The axon of the motor neurone branches when?

A

It nears its terminations and each branch ends in a special type of synapse called the neuromuscular junction

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18
Q

How many types of skeletal muscle fibre are there?

A

3

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19
Q

Describe type 1 skeletal muscle fibres

A
  • relatively slowly contracting fibres that depend on oxidative metabolism (aerobic)
  • they have abundant mitochondria and myoglobin, are resistant to fatigue and produce relatively less force
  • often called red fibres
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20
Q

Describe type 2a skeletal muscle fibres

A
  • this is intermediate between the other two
  • they are relatively fast contracting, but are also reasonably resistant to fatigue
  • these fibres are relatively uncommon
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21
Q

Describe type 2b skeletal muscle fibres

A
  • fast contracting fibres that depend on anaerobic metabolism
  • they have few mitochondria and less myoglobin than type 1 fibres
  • they fatigue relatively easily and produce relatively greater force
  • often called white fibres
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22
Q

Describe cartilage

A
  • semi rigid and deformable
  • permeable
  • avascular
  • cells nourished by diffusion through the extracellular matrix
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23
Q

Describe bone

A
  • rigid
  • not permeable
  • cells within the bone must be nourished by blood vessels that pervade the tissue
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24
Q

The cells found in cartilage are called what?

A
  • chondrocytes

- chondroblasts when immature

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25
Q

Describe chondrocytes

A
  • 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
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26
Q

Describe the composition of the ECM in hyaline cartilage

A
  • 75% water

- 25% organic material

27
Q

Describe the composition of the organic material of the ECM

A
  • 60% type 2 collagen

- 40% proteoglycan aggregates

28
Q

Describe type 2 collagen

A
  • differs from type 1 collagen, which is the most common form found in most connective tissues (eg tendon)
  • it is finer and instead of aggregating into liner bundles, it forms a 3d meshwork
  • gives resistance to tearing and structural integrity
29
Q

Describe proteoglycan aggregates

A
  • made up of GAGs (most commonly keratan sulfate and chondroitin sulfate)
  • bound to a core protein and often linked to hyaluronana
30
Q

What provides resistance to compression for cartilage?

A
  • due to proteoglycan aggregates
  • sugary molecules that become highly hydrated
  • the extra water produces a pressure within the tissue which resists compression
31
Q

Name the three types of cartilage

A
  • hyaline cartilage
  • elastic cartilage
  • fibrocartilage
32
Q

Describe hyaline cartilage

A
  • blue white in colour and translucent

- the most common form of cartilage

33
Q

Describe elastic cartilage

A
  • light yellow in colour
  • the addition of elastic fibres makes it quite flexible
  • ear, epiglottis etc
34
Q

Describe fibrocartilage

A
  • hybrid between tendon and hyaline cartilage
  • it has bands of densely packed type 1 collagen interleaved with rows of chondrocytes surrounded by small amounts of cartilaginous ECM
  • fibrocartilage appears white
  • found at symphysis, both compressible and strong
35
Q

Name places where hyaline cartilage is found?

A
  • articular surfaces
  • tracheal rings
  • costal cartilage
  • epiphyseal growth plates
  • precursor in foetus to many bones
36
Q

Describe the functions of bone

A
  • support
  • levers for effective movement
  • protection of internal organs (eg cranium, ribs)
  • calcium store; more than 95% of the total calcium in the body is found in bone and there is constant exchange of calcium between bone and the blood
  • haemopoiesis
37
Q

Name the sites of haemopoiesis

A
  • in utero blood is produced in liver and spleen, it begins in the bone marrow well before birth
  • by birth bone marrow is the main site
  • by the early twenties typically only the axial and limb girdle skeleton is involved in blood production
38
Q

Describe the composition of bone

A
  • 23% collagen
  • 2% non collagen proteins
  • 10% water
  • 65% bioapatite (a form of calcium phosphate, mostly hydroxyapatite)
39
Q

What makes up the shaft (diaphysis)?

A

An outer shell of dense cortical bone

40
Q

What occupies the ends of the bone (epiphyses)

A

Cancellous or trabecular bone

41
Q

What is cancellous bone?

A

A fine meshwork of bone - looks a bit like the inside of an aero bar

42
Q

What is lamellar bone?

A
  • made up of layer
  • circular layers around a centre
  • centre is haversian canal
43
Q

Where do haversian canals run?

A

Alon the long axis of the bone

44
Q

What direction do volkmanns canals run?

A

Transversely

45
Q

The periosteum and endosteum are involved in what?

A

Repair

46
Q

Describe the osteon

A
  • layers change orientation with each layer

- precise control of type 1 collagen fibres

47
Q

Name the main differences of the bone cells and matrix in compact and trabecular bone

A
  • presence of spaces (marrow cavities) adjcaent to trabecular bone
  • both types are lamellar
48
Q

Bone is penetrated by small canals which contain what?

A
  • blood vessels and nerves

- it contains living cells called osteocytes

49
Q

Bone is penetrated by small canals, what are they called?

A

Lacuna

50
Q

What are canaliculi?

A
  • tiny pores in bone
  • filled with tiny cell processes extendin to haversian canal
  • or it can extends to meet other processes of other cells
  • creates a network to transfer nutrients
51
Q

What are cement lines?

A
  • the lines that are often visible surrounding the osteon are termed cement lines
  • these are only found in osteons that have formed during remodelling (so not in original development)
52
Q

What type of bone generally lacks haversian canals and why?

A
  • trabecular bone

- the struts are thing, the osteocytes can survive from contact with the marrow spaces

53
Q

What are osteoprogenitor cells?

A
  • located on bone surfaces, for example under the periosteum
  • these cells serve as a pool of reserve osteoblasts
54
Q

What are osteoblasts?

A
  • bone forming cells found on the surface of developing bone
  • they have plentiful RER and prominent mitochondria
55
Q

What are osteocytes?

A
  • a bone cell trapped within the bone matrix

- cells of mature bone

56
Q

What are osteoclasts?

A
  • large multinucleated cells

- they are found on the surface of bone and are responsible for bone resorption

57
Q

Describe the remodelling of bone

A
  • bone is constantly undergoing remodelling
  • 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
  • this process continues until only the space of a haversian canal remains
58
Q

Describe bone mineralisation

A
  • the osteoblasts secrete collagen, glycosaminoglycan (GAGs), proteoglycans and other organic components of the matrix which is collectively termed osteoid
  • this then becomes mineralised over time in the extracellular space
59
Q

The mineral of bone is made up principally of what?

A

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

60
Q

Osteoclasts are believed to be derived from where?

A
  • from the macrophage lineage of cells

- several of these cells will fuse and form a single giant cells

61
Q

Younger osteons often partially obliterate what?

A

Older osteons

62
Q

What type of bone is first laid down after a break?

A
  • woven bone

- faster to lay down, overtime is remodelled

63
Q

Describe woven bone

A
  • it differs from normal lamellar bone becuase rather than having collagen fibres orientated all in one direction, as occurs in lamellar bone, 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

MSK (10 decks)

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