Musculoskeletal SystemSugito Wonodirekso, MS, DrDepartment of HistologyFMUI

Musculoskeletal System 2

Materials

Skeletal muscle Joint• Joint types• Bone• Cartilages• Supporting tissues

12/7/2008

Musculoskeletal System 3

Objectives of the muscle tissue Identify skillfully the skeletal muscle structure Identify the structural and functional different between

3 major types of muscle tissue Comprehend the relationships between muscle

fascicles, muscle fibers, myofibrils, and myofilaments Explain the structure and function of T-tubule in

skeletal muscle Analyze the relationships between normal structure and

function of skeletal muscle Explain the regeneration process of skeletal muscle

12/7/2008

Musculoskeletal System 4

General features of muscle tissues Terminology

• Prefixes: Sarco- and or myo- Specialized for contraction

• Myofilaments: actin (thin) and myosin (thick) Mesodermal origin

• Exception: iris smooth muscle arise from ectoderm Cell shape

• May reach 4 cm long called fibers (myofibers) Organization

• Works in groups or separately Two major types

• Smooth and striated

12/7/2008

Musculoskeletal System 5

Muscle types and characteristics Features Skeletal muscle

(Striated voluntary)Cardiac muscle(Striated, involuntary)

Smooth muscle(Non-striated)

Cells Thick, long, cylindric unbranched

Branched, cylindric Small, spindle-shape

Nuclei per cell

Many, peripheral One or two, central One, central

Filament ratio 6 thin/1 thick 6 thin/1 thick 12 thin/1 thick

Sarcoplasmic reticulum and myofibrils

Highly organized sarcoplasmic reticulum surrounds myofibrils

Less organized sarcoplasmic reticulum; no distinc myofibrils

Poorly organized sarcoplasmic reticulum; no distinc myofibrils

T-tubules At A-I junction; form triads

At Z lines; form dyads None

Motor end-plates

Present Absent Absent

Motor control Voluntary Involuntary Involuntary

Other Prominent fascicles Intercalated disks at cell-to-cell junctions

Abundant caveolae

Thick perimysium and epimysium

Cell overlap

12/7/2008

Musculoskeletal System 6

Skeletal muscle (this is our concern now)

Histogenesis• Mesenchymal cells of mesodermal origin fuse to

each other to make• Myoblasts which then fuse to make• Myotubes which later • Elongate by incorporating additional myoblasts• Eventually accumulated myofilaments which are

organized into myofibrils and displaced nuclei and other cytoplasmic components peripherally

12/7/2008

Musculoskeletal System 7

Skeletal muscle cells Mature skeletal muscle fibers:

• Elongated• Unbranched• Cylindrical• Multinucleated• Flattened peripherally displaced nuclei, lie just under sarcolemma

(muscle cell plasma membrane)• Most organelles and sarcoplasm (muscle cells cytoplasm) are

displaced near the nuclei’s poles• Sarcoplasm contains mitochondria, glycogen granules, and myoglobin

(oxygen-binding protein). It accumulates lipofuscin pigment with age• Mature skeletal cell are end cells and cannot divide

12/7/2008

Musculoskeletal System 8

Skeletal muscle tissue Cross-cut of skeletal muscle to show

connective tissue partitioning of muscle into groups or bundles of fibers. Endomysium is very delicate and lies between individual fibers, while perimysium is more visible and lies around a group of fibers. Epimysium is not seen here but ensheaths a whole muscle. In this picture notice the presence of small blood vessels in both perimysium and endomysium. Notice also the cross-cuts of myofibrils within the muscle cells, making them look grainy.

12/7/2008

Musculoskeletal System 9

Higher power of skeletal muscle for details of cross-striations. Notice thin Z discs and heavy A bands. From one Z disc to the next is a sarcomere, the unit of muscle contraction. In the upper muscle cell notice shadowy myofibrils running longitudinally.

12/7/2008

Musculoskeletal System 10

Skeletal muscle cells (fibers), with cross-striations and peripheral nuclei.

12/7/2008

Musculoskeletal System 11

Muscle fibers organization

12/7/2008

Musculoskeletal System 12

Sarcomeres (contraction units)

12/7/2008

Musculoskeletal System 13

Sarcomere and the cross sections

12/7/2008

Musculoskeletal System 14

Myofilament Thin filaments (actin)• Filamentous actin (F-actin) is polymeric chain of globular

actin (G-actin) monomer. Each thin filament consist of 2 double helix wound F-actin strands

• Tropomyosin is long, thin, double-helical polipeptides that wrap around the actin double helix, lies in grooves on its surface, and spans 7 G-actin monomers

• Troponin is a complex of 3 globular proteins. o TnT (Troponin T) attaches each complex to specific site on each

tropomyosin molecule, o TnC binds calcium ions, and o TnI inhibits the interaction between the thin and thick filaments

12/7/2008

Musculoskeletal System 15

Actin filaments

12/7/2008

Musculoskeletal System 16

Myofilament Thick filaments (myosin):

• Long golf-club-shaped polypeptide• A bundles of myosin molecules with their shafts pointing toward and

overlapping in the bundle’s middle and their heads projecting from the bundle’s ends

• This arrangement leaves a headless region in the center of each filament corresponding to the H band

• Treating myosin molecule with papain (a proteolytic enzyme) cleaves them, at a point near head, into 2 pieces

• The piece containing most of the thin shaft is termed light meromyosin; the head and the associated portion of the shaft make up the heavy meromyosin

• The head portion of heavy meromyosin has an ATP-binding site and an actin binding site, which are necessary for contraction

12/7/2008

Musculoskeletal System 17

Actin and myosin filaments relationship

12/7/2008

Musculoskeletal System 18

Myofilament

Organization• The banding pattern of skeletal muscle reflects the

grouping of myofilaments into parallel bundles of thin and thick filaments called myofibrils. Each muscle fiber may contain several myofibrils; the number depending on its size.

• Take special attention on the appearance of myofibrils in cross- and longitudinal section, especially in EM images and its schematic version

12/7/2008

Musculoskeletal System 19

Sarcomere and muscle contraction Diagram of contraction of skeletal

muscle. On the left is the view with light microscopy. On the right are the thin actin filaments and thick myosin filaments seen in EM. Notice that the total width of the A band stays the same throughout and that the sliding in or out of the actin filaments determines the width of the H band. Consider which filaments you would see if you cut the muscle cross-wise through the I band, A band, or H band.

12/7/2008

Musculoskeletal System 20

T-tubules and the Triads Drawing of relationship (at EM level)

of myofibrils to sarcoplasmic reticulum (smooth ER) and T-tubules in skeletal muscle. In this drawing the sarcoplasmic reticulum is labelled "sarcotubules" and "terminal cisternae". Notice that T-tubules are extensions of the sarcolemma (cell membrane, seen at right-hand edge), so that depolarization can spread along this part of the sarcolemma as well. (See diagrams and further explanation in your textbook.)

12/7/2008

Musculoskeletal System 21

The sarcomere and the diads Same diagram, for cardiac muscle. Note differences with skeletal muscle in:

• their amount and arrangement of sarcoplasmic reticulum

• the presence or near-absence of terminal cisterns (next to the T-tubules)

• the position of T-tubules in relation to the A, I, and Z bands seen at the left.

A triad consists of two terminal cisterns with a T-tubule in the middle. When the cisterns are not well developed, a true triad does not exist. A diad means two elements are together, as with one T-tubule and a neighboring bit of sarcoplasmic reticulum. NOTE: sarcoplasmic reticulum is just a form of smooth endoplasmic reticulum (SER). In muscle it is particularly associated with the release of calcium ions needed for contraction.

12/7/2008

Musculoskeletal System 22

The sarcomere EM of several myofibrils running

longitudinally through skeletal muscle cell. Between individual myofibrils lie the mitochondria (M) and glycogen (G) of the cytoplasm. Within each myofibril are the typical striations: • A= A band; • I= I band; • Z= Z line; and • H= H band.

The banding is formed by the arrangement of myosin and actin filaments.

12/7/2008

Musculoskeletal System 23

Sarcomere and the contraction

12/7/2008

Musculoskeletal System 24

Skeletal muscle regeneration

12/7/2008

Musculoskeletal System 25

Skeletal muscle regeneration

12/7/2008

Musculoskeletal System 26

Skeletal muscle regeneration

12/7/2008

Musculoskeletal System 27

Contraction process-1

12/7/2008

Musculoskeletal System 28

Contraction process-2

12/7/2008

Musculoskeletal System 29

Contraction process-3

12/7/2008

Musculoskeletal System 30

Muscle fibers organization

12/7/2008

Musculoskeletal System 31

JointsBasic joint components are:1. Bone2. Hyaline Cartilage3. Dense collagen

tissues

12/7/2008

Musculoskeletal System 32

BoneEndochondral bone formation

12/7/2008

Musculoskeletal System 33

BoneEndochondral bone formation

12/7/2008

Musculoskeletal System 34

Bone growth and remodelling

12/7/2008

Musculoskeletal System 35

Compact bone with Haversian system

12/7/2008

Musculoskeletal System 36

Haversian Lamelae and the remnant

12/7/2008

Musculoskeletal System 37

Osteocytes’ lacunae and its canaliculi

12/7/2008

Musculoskeletal System 38

Osteocyte and the canaliculi

12/7/2008

Musculoskeletal System 39

OsteocyteEM. Osteocyte in its lacuna. Notice the pericellular space, organell some of which are globules containing Calcium, and the cell processes

12/7/2008

Musculoskeletal System 40

Tight junction between osteocytes’ processes in its canaliculus

12/7/2008

Musculoskeletal System 41

Muscle-bone attachment

12/7/2008

Musculoskeletal System 42

Younger compact bone tissue

12/7/2008

Musculoskeletal System 43

Bone dynamics

Appositional growth Bone vascular system

12/7/2008

Musculoskeletal System 44

Bone

Osteocytes Compact bone tissue

12/7/2008

Musculoskeletal System 45

Hyaline cartilage

12/7/2008

Musculoskeletal System 46

Cartilage

Chondrocyte Appositional growth

12/7/2008

Musculoskeletal System 47

Cartilage

Hyalin cartilage Elastic cartilage

12/7/2008

Musculoskeletal System 48

Cartilage

Elastic cartilage Fibrous cartilage

12/7/2008

Musculoskeletal System 49

Cartilage

Hyalin cartilage Hyalin cartilage on the joint surface

12/7/2008

Musculoskeletal System 50

Joint

12/7/2008

Musculoskeletal System 51

Bone

Highly vascularized Dynamic tissue Regenerate completely

12/7/2008

Musculoskeletal System 52

Cartilage

Avascular Regenerate poorly

12/7/2008

Musculoskeletal System 53

Joint supporting tissues

Mostly dens collagen connective tissues Regenerate fairly good but not as good as

bone

12/7/2008

Musculoskeletal System 54

How joints working

Vertebrates move by application of the principles of the lever. Levers amplify or increase the force or velocity of motion. The amount of amplification depends on the length of the lever. There are three types of skeletal system, all interact with muscles using the lever.

12/7/2008