Histology 1 - MSK histology Flashcards
What are the 3 principle types of muscle?
Skeletal/ voluntary
Cardiac
Smooth
Are skeletal muscle cells striated or unstriated?
Striated
What are the names of the bundles of muscle fibres?
Fasicles
What is the name of the connective tissue that surrounds the entire muscle?
Epimysium
What is the name of the connective tissue around a single fasicle?
Perimysium
What is the name of the connective tissue around a single muscle fibre?
Endomysium
What causes the striated appearance of skeletal muscle?
The organisation of the contractile units (sarcomere) - the sarcomeres in the myofibrils with their alternating dark and light bands, are held in registry with one another across the fibre (Z-diskss in the sarcomere of one myofibril will be aligned with Z-disks of the sarcomeres in the surrounding myofibrils) - nothing is physically running across the fibre
What are the units of contraction within muscle fibres?
Sacromeres (thousands of these in a single muscle cell) - smallest contractile elements in striated muscle cell
What is the name of the structure formed when thousands of sarcomeres are packed end to end in a muscle cell?
myofibril
What is a sarcomere in terms of actin and myosin?
One Z disc to another Z disc
What is a motor unit?
One motor neurone and all the muscle fibres that it innervates (anywhere from a few to more than a hundred fibres)
Does fewer muscle fibres in a motor unit cause more fine or less fine control of movement?
More fine
The axon of the motor neurone branches as it nears its termination and each branch ends in a special type of synapse called?
The neuromuscular junction
Are the fibres in a motor unit bunched together?
No, they are scattered in the muscle
Are the fibres in a motor unit of the same fibre type?
Yes
What are the names of the 3 types of skeletal muscle fibres?
Type I
Type IIa
Type IIb
Describe type I skeletal muscle fibres?
Relatively slowly contracting fibres that depend on oxidative metabolism
They have abundant mitochondria, are resistant to fatigue and produce relatively less force
Is cartilage or bone permeable?
Cartilage is permeable, bone is not permeable
Is cartilage or bone avascular?
Cartilage = avascular Bone = cells within the bone must be nourished by blood vessels that pervade the tissue
How is cartilage nourished?
Diffusion through the extracellular matrix
Name for the cells founds in cartilage?
Name for these cells when they are immature?
Chondrocytes
Chondroblasts
Where do chondrocytes live?
Within a space in the extracellular matrix termed a lucana
What do chondrocytes do?
Active cells which not only secrete, but also maintain the extracellular matrix around them
What are the 3 common types of cartilage?
Hyaline cartilage
Elastic cartilage
Fibrocartilage
What type of cartilage is grossly, blue-white in in colour and translucent - most common form?
Hyaline cartilage
What type of cartilage is mainly light yellow in colour?
What does it have added that makes it quite flexible?
Elastic cartilage
Elastic fibres
What type of cartilage forms hybrid between tendon and hyaline cartilage - grossly appears white?
Fibrocartilage
What is the structure of fibrocartilage?
Bands of densely packed type I collagen interleaved with rows of chondrocytes surrounded by small amounts of cartilaginous ECM
Purpose of bone?
Support Levers for effective movement Protection of internal organs Calcium store Haemopoiesis (blood cell production)
How much calcium is stored int the bone?
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
Where does the Haemopoiesis occur?
In utero blood is produced in the liver and spleen
It begins in the bone marrow well before birth and by birth bone marrow is the site of haemopoiesis
By early 20s typically only in the axial and limb girdle skeleton is involved in blood production
Are skeletal muscle fibres branches or unbranched?
Unbranched
Are skeletal muscle fibres multinucleated?
What do they form?
What does this mean?
yes
Form a synctium
A single cell or cytoplasmic mass containing several nuclei, formed by fusion of cells or by division of nuclei
Approximate diameter and length of a skeletal muscle fibre?
Approx. 10-100 micro m in diameter
approx 1,000 - 200,000 micro metres in length
Where are the nuclei located in a skeletal muscle fibre?
At the periphery of the fibre, just under the cell membrane
What is the name of the cell membrane in skeletal muscle cells?
Sarcolemma
Apart from skeletal muscle, what other type of muscle is striated?
Cardiac muscle
What is another name for type I skeletal muscle fibres (aerobic)?
Red fibres
Describe type IIA skeletal muscle fibres (Intermediate)?
Intermediate between the other two
Relatively fast contracting but also reasonably resistant to fatigue (relatively uncommon)
Describe type IIB skeletal muscle fibres?
Fast contracting fibres that depend on anaerobic metabolism 0 they have few mitochondria, fatigue relatively easy and produce relatively greater force
Other name for type IIB skeletal muscle fibres (anaerobic)?
White fibres
What stain is used to identify the different types of skeletal muscle fibres?
Succinate dehydrogenase stain
Appearance of the different type of muscle fibres using succinate dehydrogenase stain?
Type 1 (aerobic) = Dark Type IIa (intermediate) = intermediate between dark and light Type IIb = Light
What is the composition of the ECM in hyaline cartilage (the most common form of cartilage)?
75% water
25% organic material (60% type II collagen, 40% proteoglycan aggregates)
What is the common form of collagen found in most connective tissue?
Type I collagen
How does type II collagen differ from type I collagen?
It is finer and instead of aggregating into linear bundles, it forms a 3D meshwork
What are proteoglycan aggregates made up of?
GAGs (Most common keratin sulphate and chondroitin sulphate) bound to a core protein and often linked to hyaluronan
5 places where hyaline cartilage is found?
Articular surfaces Tracheal rings Costal cartilage Epiphyseal growth plates Precurosor in fetus to many bones
What is the composition of bone?
65% = mineral (calcium hydroyapatite crystals) 23% = collagen 10% = water 2% = non-collagen proteins
What type of bone can be recognised with the naked eye in a longitudinal section through a long bone?
An outer shell of dense cortical/ compact bone (forms the main part of the shaft/ diaphysis)
Cancellous/ trabecular bone (occupies the ends of the bone/ epiphyses)
What are the main differences between compact/ cortical bone and cancellous/ trabecular bone?
Presence of spaces (marrow cavities) adjacent to trabecular bone - bone cells and matrix are similar
Lacks haversian canals (osteocytes can survive from contact with the marrow spaces)
What type of bone are lamellar?
Both (made up of layers)
What are the living cells in bone called?
Osteocytes
What are lacunae?
A cavity/ unfilled space
What do Haversion canals do?
Carry blood vessels in the long axis of the bone
What do Volkmann’s canals do?
Carry blood vessels in the horizontal axis of bone
What are osteons?
The functional unit of cortical bone (basic structural unit)
What are canaliculi?
Microscopic canals between the lacunae of ossified bone - radiating processes of osteocytes project into these
What are cement lines?
Line that are often visible surrounding the often - only found in osteons that have formed during remodelling (not formed in original development)
What are the 4 cells of bone?
Osteoprogenitor cells
Osteoblasts
Osteocytes
Osteoclasts
What are osteoprogenitor cells?
Cells found on bone surfaces, for example under the periosteum, that serve as a pool of reserve osteoblasts
What are osteoblasts?
Bone forming cells found on the surface of developing bone - they have plentiful RER and prominent mitochondria
What are osteocytes?
A bone cell trapped within the bone matrix
What are osteoclasts?
Large multinucleated cells
Found on the surface of bone and are responsible for bone resorption
What happens during bone remodelling?
A number of osteoclasts will congregate and begin to drill into the bone forming a tunnel
A blood vessel will grow into the tunnel brining with it osteoclasts which line the tunnel and begin laying down new lamellar bone
This process continues until only the space of a Haversian canal remains
What do osteoblasts secrete?
Collagen Glycosaminoglycans (GAGs) Proteoglycans Other organic components of the matrix This is collectively termed osteoid This becomes mineralised over time in the extracellular space
What are osteoclasts believed to be derived from?
The macrophage lineage of cells - several of these will fuse and form a single giant cells
What is the name of the type of bone that is laid down following a break/ during development?
Woven bone
How does woven bone differ in appearance to normal bone?
Rather than the collagen fibres orientated all in one direction (at least within a single lamella - the angle of deposition changes with each lamellae), the collagen fibres are laid down in a haphazard fasion
How is woven bone remodelled into lamellar bone?
By being broken down by osteoclasts and reformed by new osteoblasts
