Muscle And Bone

Question 1

4 classes of muscles

Answer 1

Cardiac
Smooth
Skeletal
Myoepithelial

All are intermingled with non muscle cells = muscle tissue

Question 2

Describe the connective tissue in skeletal muscle

Answer 2

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

Question 3

Describe the connection between muscles and tendons

Answer 3

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)

Question 4

Formation of myotubes

Answer 4

Myoblasts proliferate with a growth factor

Myoblasts differentiate and fuse to form a myotube

Question 5

Describe satellite cells, resident muscle stem cells

Answer 5

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

Question 6

Importance of satellite cells

Answer 6

Muscle growth after birth
Muscle maintenance
Hypertrophy
Repair and regeneration

Question 7

Describe the structure of sarcomeres, the contractile unit of skeletal muscle

Answer 7

Myofibrils consist of
-Thick myosin filaments
-Thin actin filaments
This results in their striated appearance
Many myofibrils form a myofibrils

Question 8

Describe the organisation of sarcomeric organisation

Answer 8

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

Question 9

How are muscles innervated

Answer 9

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

Question 10

Propagation of action potential from motor neurone

Answer 10

Action potential spreads along sarcolemma down T tubules

T tubule depolarisation causes the sarcoplasmic reticulum to release Ca2+ which will bind to troponin

Question 11

Describe cardiac tisssue
Structure
Innervation

Answer 11

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

Question 12

Describe the structure of cardiac myocytes

Answer 12

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

Question 13

Describe smooth muscle
Structure
Innervation

Answer 13

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

Question 14

Describe the structure of smooth myocytes

Answer 14

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

Question 15

What are the 2 types of hard connective tissue

Answer 15

Cartilage

Bone

Question 16

Describe hyaline cartilage

Answer 16

Fibroblasts in perichondrium, can give rise to chondrocytes in apposition all growth
Chondrocytes in matrix proliferate in interstitial growth

Question 17

Composition of cartilage
By volume
Organic components

Answer 17

Organic 25%
Water 75%
By volume

Collagen II 60%, provides tensile strength
GAG 40%, coupled to proteins => proteoglycans, gives resistance to compression, electro osmotic

Question 18

Composition of bone (mineralised connective tissue)
By weight
By volume

Answer 18

Inorganic 60%
Organic 25%
Water 15%
By weight

Inorganic 36%
Organic 36%
Water 28%
By volume

Question 19

Bone composition

Inorganic

Answer 19

Many hydroxyapatite (Ca10 (PO4)6 (OH)2)

• Needle like crystals or thin plates
• 8nm thick, variable length

Question 20

Bone composition

Organic

Answer 20

90% T1 collagen
Other proteins (osteocalcin, osteopontin, osteonectin, proteoglycans)

Question 21

Properties of cartilaginous matrix

Answer 21

Deformable (semi rigid)

Permeable to water and small molecules

Question 22

Properties of bone matrix

Answer 22

Rigid

Impermeable

Question 23

Consequences of cartilaginous properties (deformable, water and small molecule permeable)

Answer 23

Cartilage can enlarge by both appositional and interstitial growth
Cartilage does not need blood supply, nutrients via diffusion

Question 24

Consequences of the properties of bone matrix (rigid, impermeable)

Answer 24

Bone can only enlarge by appositional growth

Bone requires a blood supply

Question 25

Functions of bone

Answer 25

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

Question 26

Describe the structure of bone

Answer 26

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

Question 27

Describe the Haversian systems

Answer 27

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

Question 28

Structure of compact bone

Answer 28

Lamellar

• Collagen laid in sheets (5um), alternate orientations
• Between sheets of collagen, give increased strength

Question 29

2 major patterns of compact bone

Answer 29

Circumferential, layers surrounding bony surface at periosteum, endosteal surface

Haversian system (osteon), small concentric layers around central vascular canal

Question 30

Describe the structure of cancellous (spongy) bone

Answer 30

Supposed lamellar form trabeculae (50um)

Aligned along stress lines, maximises resistance to force, adding minimally to bone mass

Question 31

Types of bone cells

Answer 31

Osteoprogenitor cells (mesenchymal origin)
Osteoblasts
Osteocytes
Bone lining cells
Osteoclasts (from haemopoietic stem cells)

Question 32

Describe osteoprogenitor cells

Answer 32

Mesenchymal fibroblast like, stem cell population
In trabecular bone, found near blood vessels
In compact bone, found at periosteum and endosteum

Question 33

Describe osteoblasts

Answer 33

On bone surface, responsible for steal deposition (component of bone matrix)
Extensive RER, Golgi, mitochondria, vesicles
Cells have desmosomes, gap junctions

Question 34

Function of osteoblasts

Answer 34

Induce mineralisation through secretion of matrix vesicles

Contain alkaline phosphatase, neutralises inhibitory effects of pyrophosphate on calcium deposition

Question 35

Describe osteocytes

Answer 35

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

Question 36

Function of osteocytes

Answer 36

Role of calcium homeostasis
Respond to mechanical forces
Mediate mechanically adaptive bone remodelling, act as strain receptors

Question 37

Describe the bone lining cells

Answer 37

Undifferentiated, flat
Found at bone surface under quiescence (not being remodelled)
May represent inactive osteoblasts and have important functions

Question 38

Describe osteoclasts

Answer 38

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

Question 39

Formation of Haversian systems

Answer 39

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

Question 40

Step 1 of endochondral ossification

Bone collar formation

Answer 40

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

Question 41

Step 2 of endochondral ossification

Cavitation

Answer 41

Chondrocytes enlarge and signal for hyalin to calcify into bone
Calcified hyalin=impermeable to nutrient diffusion and die
Results in cavities for blood vessels

Question 42

Step 3 of endochondral ossification

Periosteum bud invasion

Answer 42

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

Question 43

Step 4 of endochondral ossification

Diaphysis elongation

Answer 43

Diaphysis elongates, powered by dicing cells in primary ossification center
Elongated region=medullary cavity, bone marrow forms here

Question 44

Step 5 of endochondral ossification

Epiphyseal ossification

Answer 44

Epiphysis develops own ossification center wtith its own periosteal bud
Growth plate is between 2 ossification centres

Question 45

Step 1 of intramembranous ossification

Formation of ossification center

Answer 45

Mesenchymal cells from embryonic skeleton differentiate into osteoblasts
Osteoblasts secrete osteoid

Question 46

Step 2 of intramembranous ossification

Formation of osteocytes

Answer 46

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

Question 47

Step 3 of intramembranous ossification

Formation of trabecular matrix

Answer 47

Many osteoid clusters unite around capillaries => trabecular matrix
Osteoblasts on the surface = cellular layer of periosteum
Periosteum secretes compact bone

Question 48

Step 4 of intramembranous ossification

Formation of red bone marrow

Answer 48

Spongy bone crowds around blood vessels

Blood vessels condense into red bone marrow