Histology Flashcards
1
Q
Name the three principle types of muscle
A
- skeletal or voluntary
- cardiac
- smooth
2
Q
What is the sarcolemma?
A
Plasma membrane of a muscle cell
3
Q
Where are the nuclei found in skeletal muscle fibres?
A
At the periphery of the fibre, just under the cell membrane (sarcolemma)
4
Q
Muscle fibres are grouped into bundles called what?
A
Fascicles
5
Q
What is the epimysium?
A
The connective tissue that surrounds the muscle as a whole, outer layer
6
Q
Each fascicle is made up of what?
A
Packed muscle cells
7
Q
What is the perimysium?
A
The connective tissue around a single fascicle
8
Q
What is the endomysium?
A
The connective tissue around a single muscle fibre. Wispy connective tissue
9
Q
Each muscle fibre contains many what?
A
Myofibrils
10
Q
Each myofibril consists of what?
A
Many sarcomeres placed end to end
11
Q
What is the unit of contraction within muscles?
A
Sarcomeres
12
Q
By definition, the sarcomere extends from where?
A
From one Z line to the next
13
Q
What is the I band?
A
Actin thin filaments anchored to a central line (z line)
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
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)
16
Q
The fewer the number of muscle fibres in a motor unit …..
A
The finer the control of the movement
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
18
Q
How many types of skeletal muscle fibre are there?
A
3
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
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
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
22
Q
Describe cartilage
A
- semi rigid and deformable
- permeable
- avascular
- cells nourished by diffusion through the extracellular matrix
23
Q
Describe bone
A
- rigid
- not permeable
- cells within the bone must be nourished by blood vessels that pervade the tissue
24
Q
The cells found in cartilage are called what?
A
- chondrocytes
- chondroblasts when immature
25
Describe chondrocytes
- 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
26
Describe the composition of the ECM in hyaline cartilage
- 75% water
| - 25% organic material
27
Describe the composition of the organic material of the ECM
- 60% type 2 collagen
| - 40% proteoglycan aggregates
28
Describe type 2 collagen
- 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
Describe proteoglycan aggregates
- made up of GAGs (most commonly keratan sulfate and chondroitin sulfate)
- bound to a core protein and often linked to hyaluronana
30
What provides resistance to compression for cartilage?
- due to proteoglycan aggregates
- sugary molecules that become highly hydrated
- the extra water produces a pressure within the tissue which resists compression
31
Name the three types of cartilage
- hyaline cartilage
- elastic cartilage
- fibrocartilage
32
Describe hyaline cartilage
- blue white in colour and translucent
| - the most common form of cartilage
33
Describe elastic cartilage
- light yellow in colour
- the addition of elastic fibres makes it quite flexible
- ear, epiglottis etc
34
Describe fibrocartilage
- 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
Name places where hyaline cartilage is found?
- articular surfaces
- tracheal rings
- costal cartilage
- epiphyseal growth plates
- precursor in foetus to many bones
36
Describe the functions of bone
- 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
Name the sites of haemopoiesis
- 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
Describe the composition of bone
- 23% collagen
- 2% non collagen proteins
- 10% water
- 65% bioapatite (a form of calcium phosphate, mostly hydroxyapatite)
39
What makes up the shaft (diaphysis)?
An outer shell of dense cortical bone
40
What occupies the ends of the bone (epiphyses)
Cancellous or trabecular bone
41
What is cancellous bone?
A fine meshwork of bone - looks a bit like the inside of an aero bar
42
What is lamellar bone?
- made up of layer
- circular layers around a centre
- centre is haversian canal
43
Where do haversian canals run?
Alon the long axis of the bone
44
What direction do volkmanns canals run?
Transversely
45
The periosteum and endosteum are involved in what?
Repair
46
Describe the osteon
- layers change orientation with each layer
| - precise control of type 1 collagen fibres
47
Name the main differences of the bone cells and matrix in compact and trabecular bone
- presence of spaces (marrow cavities) adjcaent to trabecular bone
- both types are lamellar
48
Bone is penetrated by small canals which contain what?
- blood vessels and nerves
| - it contains living cells called osteocytes
49
Bone is penetrated by small canals, what are they called?
Lacuna
50
What are canaliculi?
- 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
What are cement lines?
- 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
What type of bone generally lacks haversian canals and why?
- trabecular bone
| - the struts are thing, the osteocytes can survive from contact with the marrow spaces
53
What are osteoprogenitor cells?
- located on bone surfaces, for example under the periosteum
- these cells serve as a pool of reserve osteoblasts
54
What are osteoblasts?
- bone forming cells found on the surface of developing bone
- they have plentiful RER and prominent mitochondria
55
What are osteocytes?
- a bone cell trapped within the bone matrix
| - cells of mature bone
56
What are osteoclasts?
- large multinucleated cells
| - they are found on the surface of bone and are responsible for bone resorption
57
Describe the remodelling of bone
- 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
Describe bone mineralisation
- 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
The mineral of bone is made up principally of what?
Calcium phosphate crystal, particularly hydroxyapatite; Ca10(PO4)6(OH)2
60
Osteoclasts are believed to be derived from where?
- from the macrophage lineage of cells
| - several of these cells will fuse and form a single giant cells
61
Younger osteons often partially obliterate what?
Older osteons
62
What type of bone is first laid down after a break?
- woven bone
| - faster to lay down, overtime is remodelled
63
Describe woven bone
- 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
