Histology - MSK Flashcards
What are the different types of muscle? Where can you find each of them?
- Visceral (smooth) muscle = arterial wall, wall of intestines, airways of lungs
- Voluntary (skeletal) muscle = skeletal muscles, larynx, diaphragm
- Cardiac muscle = heart, base of great vessels
- Other contractile cells = pericytes, myo-fibroblasts, myo-epithelial cells
How are skeletal muscle cells formed?
Formed by the fusion of primitive cells in the developing embryo called myoblasts
What do myoblasts fuse to form? What do sarcomeres form? What are cytoplasms filled with? What do groups of muscle fibres form? What are fascicles of muscle fibres held together to form?
- Multi-celled syncytium
- Sarcomeres joined end to end to form myofibrils (multiple myofibrils within each skeletal muscle cell)
- Cytoplasm filled with myofibrils to form muscle fibre
- Muscle fibres clumped together to form fascicles
- Fascicles held together to form muscles
What are the connective tissues of skeletal muscle?
- Endomycium
- Perimycium
- Epimycium
Diagram of individual myoblasts forming an individual muscle fibre.
Individual muscle fibres are multi-nucleated
What does a skeletal muscle fibre/cell contain in its cell membrane?
- Cell membrane (sarcolemma)
- Nuclei
- Contractile proteins
- Mitochondria
- Endoplasmic reticulum (sarcoplasmic reticulum)
- Glycogen-rich cytoplasm (glycogen-rich sarcoplasm)
Is skeletal muscle voluntary or involuntary? Is it striated? Does it have a single nucleus? Is it branching?
- Voluntary
- Elongated fibres with a striated cytoplasm
- Multinucleate
- Nuclei at edges
- Non-branching
Diagram of striations under different stains.
Why is skeletal muscle striated?
Myofibrils are in register
What are the two types of skeletal muscle fibres? Are they distinguishable on H+E stain?
- Type 1 = rich in fibrillar ATPase, slow twitch
- Type 2 = rich in fibrillar ATPase, fast twitch
How do muscles detect stretch and tension? What are these contained within?
- Muscle spindles
- Contained within a fibrocollagenous capsule
- Intrafusal muscle fibres (wrapped around by gamma efferent nerves)
- Detect stretch and tension
Diagram of skeletal muscle connective tissue.
How is skeletal muscle connected to bone?
- Sharpey’s fibres
- Bundles of collagen linking epimysium to periosteum
- Attach muscle to bone over a wide area, e.g. rotator cuff muscles attached to scapula
How is skeletal muscle connected to bone over a short area?
- Tendons
- Connect muscle to bone
- Parallel bundles of collagen with intervening fibroblasts
- Attach muscle to bone over a small area, e.g. rotator cuff muscles attached to humerus
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What are the cells of bone? What makes up the extracellular matrix of bone?
- Cells:
- osteoprogenitor cells
- osteoblasts
- osteocytes
- osteoclasts
- Extracellular matrix:
- collagen
- calcium hydroxyapatite
Where are osteoblasts and osteocytes derived from? What do osteoblasts secrete? What are osteocytes? How are osteoblasts connected to their neighbours?
- Derived from osteoprogenitor cells
- Osteoblasts secrete osteoid
- Osteocytes = osteoblasts that have become trapped in their own matrix
- Connect to surrounding cells via canaliculi
What are osteoclasts? What are they derived from? What is their function? What is the activity of osteoclasts and osteoblasts coordinated by?
- Multinucleate cells
- Derived from monocytes
- Absorb bone - sit in Howship’s lacunae
- RANK-L
How can describe the different types of bone?
- By origin:
- Primary (woven)
- Secondary (lamellar)
- By mode of formation:
- Membranous
- Endochondrial
- By gross appearance:
- Spongy/cancellous
- Compact
- Osteons
- Appositional
Diagram of osteoid and primary bone.
What does secondary bone form as? What do osteons contain?
- Secondary bone is stronger than primary bone
- Forms as osteons
- Osteons have a central Haversian canal donating blood vessels
- Osteons have a surrounding concentric rings of lamellar bone with osteocytes
What is secondary bone typically examined as?
Typically examined as a decalcified section
What are the two types of bone formation?
- Intramembranous = flat bones of the skull and some cortical bone shafts
- Endochondrial = all other bones
Picture of intramembranous ossification.
Picture of endochondrial ossification.
What does synovium line? What are the the two types of synovial cells? What is the shape of synovial cells? Is synovium vascular and innervated?
- Lines the inside of the joint capsule, 1-4 layers of synovial cells
- Type A = phagocytes, type B = rich in RER
- Variable shapes - squamous to cuboidal
- Synovium is richly vascular and highly innervated
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