Muscle And Bone Flashcards
4 classes of muscles
Cardiac
Smooth
Skeletal
Myoepithelial
All are intermingled with non muscle cells = muscle tissue
Describe the connective tissue in skeletal muscle
Epimysium, tough outer layer, surrounds entire muscle
Perimysium, surrounds muscle fibre bundles = fascicles
Endomysium, surrounds each muscle fibre in fasciculus
Blood vessels, nerves embedded in fascia
Describe the connection between muscles and tendons
Endo, peri, epimysium merge with dense collagen opus connective tissue of tendon at myotendinous junction
Tendons transmit muscle force to bone, skeleton moves at joints, made of collagen fibres (strong and stiff)
Formation of myotubes
Myoblasts proliferate with a growth factor
Myoblasts differentiate and fuse to form a myotube
Describe satellite cells, resident muscle stem cells
Found on muscle fibres, mitotically quiescent
Can self renew, maintain stem cell population, myonuclei can’t
Can be activated to enter the cell cycle => myoblasts
Myoblasts proliferate, differentiate
-Provide new myonuclei for existing muscle
-Fuse together to generate new myofibres
Importance of satellite cells
Muscle growth after birth
Muscle maintenance
Hypertrophy
Repair and regeneration
Describe the structure of sarcomeres, the contractile unit of skeletal muscle
Myofibrils consist of -Thick myosin filaments -Thin actin filaments This results in their striated appearance Many myofibrils form a myofibrils
Describe the organisation of sarcomeric organisation
A band, length of myosin I band, length of actin only Z line, attachment site of actin M line, attachment site of myosin H zone, length of myosin only
How are muscles innervated
Myofibres receive innervation from 1 motor neurone
Neuromusclular junction between muscle fibre membrane and nerve
Motor unit = motor neurone contacts many muscle fibres
Larger the motor unit = smaller degree of control and vice versa
Propagation of action potential from motor neurone
Action potential spreads along sarcolemma down T tubules
T tubule depolarisation causes the sarcoplasmic reticulum to release Ca2+ which will bind to troponin
Describe cardiac tisssue
Structure
Innervation
In heart, pumps blood
Controlled by ANS
Striated with sarcomeric tissue
Cells connected via intercalated discs, form functional syncytial
Fibrous connective tissue rich in blood vessels
Describe the structure of cardiac myocytes
Mono/binucleated cells, nucleus centrally located
Striated with sarcomeric structure with intercalated discs, form functional syncytial
Gap junctions allow AP transmission, many mitochondria
Many blood vessels, increased aerobic resp
No satellite cells, no regeneration
Describe smooth muscle
Structure
Innervation
In gut walls, blood vessels, resp tract, urogenital tract
Layers of alternating longitudinal, transverse layers of cells
No striations, ANS
Can stretch, maintain tension for long periods of time
Describe the structure of smooth myocytes
Spindle shaped cells, unstriated, form functional syncytial
5um diameter, 20-200um in length
Cells twist when contracted
Central mononucleated, innervated by single nerve ending
Surrounded by basal lamina
Small amounts of connective tissue between cells, nerve and vessel passage
Cytoplasm filled with actin filaments, less myosin
Myofilaments loosely organisation, attached to focal densities in cytoplasm and focal adhesion densities at membrane
What are the 2 types of hard connective tissue
Cartilage
Bone
Describe hyaline cartilage
Fibroblasts in perichondrium, can give rise to chondrocytes in apposition all growth
Chondrocytes in matrix proliferate in interstitial growth
Composition of cartilage
By volume
Organic components
Organic 25%
Water 75%
By volume
Collagen II 60%, provides tensile strength
GAG 40%, coupled to proteins => proteoglycans, gives resistance to compression, electro osmotic
Composition of bone (mineralised connective tissue)
By weight
By volume
Inorganic 60%
Organic 25%
Water 15%
By weight
Inorganic 36%
Organic 36%
Water 28%
By volume
Bone composition
Inorganic
Many hydroxyapatite (Ca10 (PO4)6 (OH)2)
- Needle like crystals or thin plates
- 8nm thick, variable length
Bone composition
Organic
90% T1 collagen Other proteins (osteocalcin, osteopontin, osteonectin, proteoglycans)
Properties of cartilaginous matrix
Deformable (semi rigid)
Permeable to water and small molecules
Properties of bone matrix
Rigid
Impermeable
Consequences of cartilaginous properties (deformable, water and small molecule permeable)
Cartilage can enlarge by both appositional and interstitial growth
Cartilage does not need blood supply, nutrients via diffusion
Consequences of the properties of bone matrix (rigid, impermeable)
Bone can only enlarge by appositional growth
Bone requires a blood supply
Functions of bone
Support
Protection
System of levers, transformed into body, movements by muscle action
Contains bone marrow
-Yellow (fat store)
Red (haemopoetic, forms blood cells)
Reservoir of Ca, PO4 3-, other ions
Describe the structure of bone
Outer layer= cortical/compact bone
Interior of epiphysis = trabecular bone
Articulate surfaces covered by articulate cartilage, no perichondrium
Non articulate surfaces covered by periosteum
Internal surfaces lined by endosteum
Medullary cavity filled with marrow, between trabeculae
Describe the Haversian systems
Constructed around central canal
4-20 concentric lamellar, surrounded by cement line of mineralised matrix
Canals connected transversely by Volkman’s canals
Interstitial lamella between osteons
Lacuna found within the concentric lamellae, canaliculi come off lacunae
Lacuna contain osteocytes
Structure of compact bone
Lamellar
- Collagen laid in sheets (5um), alternate orientations
- Between sheets of collagen, give increased strength
2 major patterns of compact bone
Circumferential, layers surrounding bony surface at periosteum, endosteal surface
Haversian system (osteon), small concentric layers around central vascular canal
Describe the structure of cancellous (spongy) bone
Supposed lamellar form trabeculae (50um)
Aligned along stress lines, maximises resistance to force, adding minimally to bone mass
Types of bone cells
Osteoprogenitor cells (mesenchymal origin)
Osteoblasts
Osteocytes
Bone lining cells
Osteoclasts (from haemopoietic stem cells)
Describe osteoprogenitor cells
Mesenchymal fibroblast like, stem cell population
In trabecular bone, found near blood vessels
In compact bone, found at periosteum and endosteum
Describe osteoblasts
On bone surface, responsible for steal deposition (component of bone matrix)
Extensive RER, Golgi, mitochondria, vesicles
Cells have desmosomes, gap junctions
Function of osteoblasts
Induce mineralisation through secretion of matrix vesicles
Contain alkaline phosphatase, neutralises inhibitory effects of pyrophosphate on calcium deposition
Describe osteocytes
Cell bodies in lacunae, result of mineralisation occurring around
Numerous canaliculi, radiate from lacuna, have osteocytes cell processes
Nucleus, thin ring of cytoplasm, few organelles, v little cellular activity
Processes joined by gap junctions for communication/coordination
Canaliculi allow substance diffusion through bone
Function of osteocytes
Role of calcium homeostasis
Respond to mechanical forces
Mediate mechanically adaptive bone remodelling, act as strain receptors
Describe the bone lining cells
Undifferentiated, flat
Found at bone surface under quiescence (not being remodelled)
May represent inactive osteoblasts and have important functions
Describe osteoclasts
Involved in bone reabsorption, highly motile
Found in reabsorption cavities (Haversian lacunae) on bone surface
Variable size/shape, from small mononuclear cells to large (>100um) multinucleated cells
Reabsorption contributes to bone remodelling and calcium homeostasis
Directly inhibited by calcitonin
Parathyroid hormone stimulates osteoblasts to release induces of osteoclasts differentiation
Formation of Haversian systems
Osteoclasts tunnel through pre existing bone
Tunnel invaded by blood vessels and osteoprogenitor cells
Osteoblasts lay down successive bone lamellae on tunnel walls
Interstitial systems are remnants of old osteons
Step 1 of endochondral ossification
Bone collar formation
Osteoblasts in bone secrete osteoid against diaphysis walls from the primary ossification centre
The hyalin diaphysis=encased in compact bone to form the bone collar
Step 2 of endochondral ossification
Cavitation
Chondrocytes enlarge and signal for hyalin to calcify into bone
Calcified hyalin=impermeable to nutrient diffusion and die
Results in cavities for blood vessels
Step 3 of endochondral ossification
Periosteum bud invasion
Bud made up of blood vessels and nerves
Allows nutrients and osteoblasts, osteoclasts to enter cavities
Osteoblasts=secrete osteoid into remaining hyalin to form spongy bone
Step 4 of endochondral ossification
Diaphysis elongation
Diaphysis elongates, powered by dicing cells in primary ossification center
Elongated region=medullary cavity, bone marrow forms here
Step 5 of endochondral ossification
Epiphyseal ossification
Epiphysis develops own ossification center wtith its own periosteal bud
Growth plate is between 2 ossification centres
Step 1 of intramembranous ossification
Formation of ossification center
Mesenchymal cells from embryonic skeleton differentiate into osteoblasts
Osteoblasts secrete osteoid
Step 2 of intramembranous ossification
Formation of osteocytes
Osteoblasts secrete osteoid (uncalcified matrix containing collagen precursors) and other organic products
Calcified, trapped osteoblasts => osteocytes
Osteopenia cells => osteoblasts at the edges of the growing bone
Step 3 of intramembranous ossification
Formation of trabecular matrix
Many osteoid clusters unite around capillaries => trabecular matrix
Osteoblasts on the surface = cellular layer of periosteum
Periosteum secretes compact bone
Step 4 of intramembranous ossification
Formation of red bone marrow
Spongy bone crowds around blood vessels
Blood vessels condense into red bone marrow
