Musculoskeletal Histology Flashcards
3 types of muscle?
Skeletal (voluntary)
Cardiac
Smooth
3 features of skeletal muscle cells/fibres?
Striated
Unbranched
Multi-nucleate (forming a synctium) - nuclei are at the fibre periphery, under the membrane (called the sarcolemma)
How are muscle fibres grouped?
Into bundles called FASCICLES
Connective tissue in skeletal muscles?
If it surrounds the muscle as a whole - epimysium
Around a single fascicle - perimysium
Around a single muscle fibre - endomysium
What are sarcomeres?
Smallest functional contractile elements; these group together to form myofibrils which, in turn, group to form the muscle fibre
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Why are skeletal muscle fibres striated?
Sarcomeres in the myofibrils, with their alternating dark and light bands, are held in registry with one another
Z-lines in the sarcomere of one myofibril will be aligned with the Z-lines of the sarcomeres in other myofibrils, so it looks like something is running across the fibre
What is a motor unit?
An α-motor neurone and all of the muscle fibres that it innervates
How do muscle fibres in a motor unit vary?
The number of fibres can vary; fewer the no. of muscle fibres in a motor unit, the finer the control of movement
However, the fibres are all of the same type and are scattered in the muscle
Junction between the motor neuron and skeletal muscle?
Axon of the motor neuron branches as it nears its termination
Each branch ends in a NEUROMUSCULAR JUNCTION
3 types of skeletal muscle fibres?
Type I - relatively slowly contracting fibres that depend on oxidative metabolism
Type IIa (uncommon) - intermediate between the other two; relatively fast contracting but also reasonably resistant to fatigue
Type IIb (AKA white fibres) -fast-contracting fibres that depend upon anaerobic metabolism; few mitochondria, fatigue easily and produce relatively great force
Compare cartilage and bone?
Cartilage is semi-rigid and deformable, avascular and cell nourished by diffusion through the EC matrix
Bone is rigid and not permeable; cells within the bone must be nourished by blood vessels that pervade the tissue
Cartilage cells?
Chondrocytes - within the lacuna (space in the EC matrix); they are active cells which secrete and maintain the EC matrix
They are called chrondroblasts when immature
Components of the ECM in hyaline cartilage (most common)?
- 75% water
- 25% organic material:
• 60% type II collagen
• 40% proteoglycan aggregates (made up of GAGs) bound to a core protein and often linked to hyaluronan
Differences between type I and II collagen?
Type I is the most common form of collagen and aggregates into linear bundles
Type II is finer and forms a 3D network
Types of cartilage?
Hyaline cartilage (most common) - grossly, blue-white in colour and transclucent
Elastic cartilage - grossly, light yellow in colour; elastic fibres make it flexible
Fibrocartilage - grossly, appears white and is a hybrid of tendon and hyaline cartilage
Bands of densely packed type I collagen inter-weaved with rows of chondrocytes are surrounded cartilagenous ECM
Examples of sites where hyaline cartilage is found?
Articular surfaces
Tracheal rings
Costal cartilage
Epiphyseal growth plates
In fetus, precursor to many bones
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Functions of bone?
- Support
- Levers for effective movement
- Protection of internal organs
- Ca2+ store
- Haemopoiesis
Describe haemopoiesis
Blood cell production
- While in utero, blood is produced in the liver and spleen but it begins in the bone marrow before birth
- By time of birth, bone marrow is the site of haemopoiesis
- By early 20s, only the axial and limb girdle skeleton is involved in blood production
Composition of bone?
Collagen, minerals, water and non-collagen proteins
Morphology of bone?
Outer shell of dense cortical bone makes up the diaphysis
Cancellous/trabecular bone occupies the epiphyses (looks like inside of an aero bar)
One similarity and one difference between compact and trabecular bone?
Both are lamellar (made up of layers)
Adjacent to trabecular bone, there are marrow cavities (spaces)
