Histology Flashcards
what is a eukaryotic cell?
a cell with a true nucleus
what are the 3 principal types of muscle?
- skeletal (voluntary)
- cardiac
- smooth
what do skeletal muscle cells look like?
- striated
- unbranched
- multi-nucleated
where are nuclei found in a muscle fibre & why?
at the periphery of the fibres just under the cep membrane because cells are so stuffed with contractile fibres, the nuclei are pushed to the side
what’s the cell membrane called in a muscle fibre?
sarcolemma
what groups are muscle fibres put into?
fascicles
what is the connective tissue that surrounds the muscle as a whole called?
epimysium
what is the connective tissue around a single fascicle called?
perimysium
what is the connective tissue around a single muscle fibre called?
endomysium
what are sarcomeres?
the unit of contraction of the muscle cell i.e. the smallest contractile elements in the striated muscle cell
how are sarcomeres normally placed in a typical muscle cell?
end-to-end to form a myofibril
how are the myofibrils packed into a muscle fibre?
dozens to hundred are packed in like cigarettes in a pack
which is the thick protein filament?
myosin
which is the thin protein filament?
actin
what does a Z disk do?
anchors actin filaments from adjacent sarcomeres to bind two sarcomeres together
what is the A band?
the length of a myosin filament, darker
what is the I line?
actin by itself, contraction causes it to get smaller due to sliding action of actin & myosin
why is skeletal muscle striated?
each sarcomere of a myofibril is held in close registry to the next one so the A, I & Z lines line up & look like stripes across the myofibrils
what does a motor unit consist of?
one motor neurone & all of the muscle fibres it innervates
what does fewer muscle fibres in a motor unit mean?
finer control of movement
what is the neuromuscular junction?
a special type of synapse where the axon of the motor neurone branches as it nears its termination
how are the fibres of a motor unit organised in the muscle?
scatters but all of the same fibre type
where is the finest control found in the body?
in the oculomotor nuerones
how many times does each muscle fibre meet the motor neurone controlling it?
once
what is type 1 skeletal muscle fibre?
relatively slowly contracting fibres that depend on oxidative metabolism. Have abundant mitochondria & are resistant to fatigue and produce relatively less force
what are type 1 muscle fibres also often called & why?
“red” fibres due to lots of myoglobin in the cells
give an example of where type 1 muscle fibres may be found in the body
the back
what are type 2a skeletal muscle fibres?
intermediated between types 1 & 2. Relatively fast contracting but also reasonably resistant to fatigue.
how common are type 2a skeletal muscle fibres?
relatively uncommon
what are type 2b skeletal muscle fibres?
fast contracting fibres that depend on aerobic metabolism. Have few mitochondria so fatigue relatively easily & produce greater force.
what are type 2b skeletal muscle fibres sometimes called?
“white” fibres
where may you find type 2b skeletal muscle fibres in the body?
the fingers
what is cartilage?
Semi-rigid and Deformable
Permeable
Avascular (no blood vessels)
how are cartilage cells nourished?
by diffusion through the extracellular matrix (outer perichondrium)
what is bone?
rigid
not permeable
how are cells in bone nourished?
must be nourished by blood vessels that pervade the tissue
what are the cells found in cartilage called?
chondrocytes (chondroblasts when immature)
where are chondrocytes found?
live within a space in the extracellular matrix termed a lacuna
what are chondrocytes & what do they do?
active cells which not only secrete, but also maintain the extracellular matrix around them
what is the most common form of cartilage?
hyaline
what is the composition of the extracellular matrix of hyaline cartilage?
- 75% water
- 25% organic material
what is the organic material found in the ECM of hyaline cartilage made up of?
- 60% type 2 collagen
- 40% proteoglycan aggregates
what is type 2 collagen?
finer than type 1 collagen & forms a 3-D meshowrok
what is type 1 collagen?
common form found in most connective tissues (e.g. tendon) which aggregates into linear bundles
what are proteoglycans made up of?
GAGs bound to a core protein & often linked to hyaluronan
what are GAGs?
most commonly keratin sulfate & chondroitin sulfate
what does hyaline cartilage look like?
blue-white colour & transluscent
what does elastic cartilage?
light yellow in colour
what gives elastic cartilage it’s flexibility?
the addition of elastic fibres
what is fibrocartilage?
hybrid between tendon & hyaline cartilage
what is fibrocartilage made up of?
bands of densely packed type 1 collagen interleaved with rows of chondrocytes surrounded by small amounts of cartilaginous ECM
what does fibrocartilage look like?
white
what are the functions of bone?
- support
- levers for movement
- protection
- Ca++ storage
- Haemopoiesis
what is haemopoiesis?
blood cell production
what are the two types of bone identifiable with the naked eye in a long bone?
cortical & cancellous/trabecular bone
what is cortical bone?
an outer dense shell which makes up the shaft of a long bone
where is cancellous bone found?
occupies the ends of the bone (epiphyses)
what does cancellous bone look like?
fine meshwork of bone
what is a aversion canal?
canal running along long axis of the bone for blood vessels surround by layer upon layer of bone
what are the outer layers of the bone called?
outer circumferential lamellae
what do the layers of bone represent?
changes in the collagen that’s laid down and the way it’s orientated (laid down similarly to plywood)
what are the living cells found in bone?
osteocytes
what are volkman’s canals?
run horizontally to deliver blood between the aversion canals
how do osteocytes get nutrients & O2?
through their dendrites which run in canaliculi & can get O2 & nutrients by being in contact with a blood vessel or another osteocyte’s dendrites
what are the lines that are often visible surrounding an osteon called?
cement lines
what is an osteon?
the tree ring ling structures with the aversion canals running in them
what are osteoprogenitor cells & where are they found?
located on bone surfaces, for example under the periosteum, these cells serve as a pool of reserve osteoblasts (precursors of osteoblasts)
what are osteoblasts & where are they found?
bone forming cells found the surface of developing bone. Have plentiful RER & prominent mitochondria
what are osteocytes & where are they found?
a bone cell trapped within the bone matrix
what are osteoclasts & where are they found?
large multinucleate cells found on the surface of bone, responsible for bone resorption
how is a bone remodelled?
a number of osteoclasts will congregate & will begin to drill into the bone forming a tunnel where a blood vessel will grow into, bringing with it osteoblasts. Osteoblasts line the tunnel & begin laying down new lamellar bone.
what is the collection of osteoclasts & osteoblasts that participate in bone remodelling called?
basic multicellular unit (BMU)
what are osteoclasts believed to be derived from?
the macrophage lineage of cells. Several of these cells will fuse and form a single giant cell.
what do osteoclasts secrete to eat away at bone?
acids & enzymes
what do osteoblasts secrete?
a type of organic material, an osteoid, which will attract collagen & minerals to it so it will mineralise & harden over time
what can younger osteons do to older osteons?
partially obliterate them when they’re forming
what bone is found in growing children or following a break?
woven bone which will then be remodelled into lamellar bone
what is the advantage of woven bone?
can be made quickly
what is the disadvantage of woven bone?
not as strong as lamellar bone
how are the collagen fibres arranged in woven bone compared to lamellar bone?
woven - haphazard nests
lamellar - carefully designed layers
