Microscopic Osteology & Myology

Functions of the skeletal system

Support, mineral storage, hemopoiesis, protection, body movement, fat and stem cells

Cells of mature bone

osteocytes, osteoblasts, osteoclasts, osteoprogenitor cells

Osteocytes

mature bone cells, maintain bone tissue

Osteoblasts

bone forming cells, osteogenesis

Osteoclasts

Bone-destroying cells, osteolysis

Osteoprogenitor cells

bone stem cells

compact bone

hard, dense bone tissue that is beneath the outer membrane of a bone

spongey bone

contains spaces that are filled with blood forming tissue, called red marrow

epiphyses

ends of long bone

diaphysis

shaft of a long bone

metaphyses

areas where the epiphyses and diaphysis join

Periosteum

- isolates the bone

- protects the bone from surrounding tissues

- provides attachment for nerves and blood vessels

- participates in bone growth and repair

- attaches the bone to connective tissue

Bone development and growth

- before 6 weeks of development bone is cartilage

- osteogenesis to ossification (calcification)

- intramembranous ossification (bone formation within mesenchyme or fibrous connective tissue)

- endochondral ossification (bone development from hyaline cartilage, bone growth in length)

Muscle Tissue

1. Excitability (ability to respond to stimuli)

2. Contractibility (ability to actively shorten)

3. Extensibility (ability to continue to contract over a range of length)

4. Elasticity (ability to rebound to its original length after deformation)

Myofilaments

The contractile proteins, actin and myosin, of muscle cells

Z line

the line formed by the attachment of actin filaments between two sarcomeres of a muscle fiber in striated muscle cells

M line

supporting proteins that hold the thick filaments together in the H zone ("middle")

H band

middle of A band; thick filaments only

Titin

A series elastic component protein responsible for allowing the sarcomere to stretch and recoil

A band

dark area; extends length of the thick filaments

I band

thin filaments only

The sliding filament theory (theory)

theory that actin filaments slide toward each other during muscle contraction, while the myosin filaments are still

The sliding filament theory (processes)

- the H band and I band get smaller

- the zone of overlap gets larger

- the Z lines move closer together

- the width of the A band remains constant

force-length relationship

length of a muscle relative to its resting length during an isometric contraction will determine the max force it can produce

Steps that initiate a muscle contraction (steps 1-5)

1. ACh released, binding to receptors

2. Action potential reaches T tubule

3. Sarcoplasmic reticulum releases Ca2+

(Ca2+ binds to troponin, moves tropomyosin)

4. Active site exposure and cross-bridge formation

5. Contraction begins (can complete power stroke)

Steps that end a muscle contraction (steps 6-10)

6. ACh removed by AChE

7. Sarcoplasmic reticulum recaptures Ca2+

(Ca2+ releases troponin, tropomyosin covered again)

8. Active sites covered, no cross-bridge interaction

9. Contraction ends

10. Relaxation occurs, passive return to resting length

fast muscle fibers

- large diameter

- contract fast

- large glycogen reserves

- few mitochondria

- fatigue easily (rely on storage)

- lighter in color (less blood supply)

slow muscle fibers

- half the diameter of fast fibers

- takes 3x as long to contract after stimulation

- contain abundant mitochondria

- uses aerobic metabolism

- surrounded by more extensive network of capillaries

- red in color

intermediate fibers

- properties between fast and slow fibers

- faster than slow / slower than fast

- similar to fast fibers except: more mitochondria, slightly increased capillary supply, greater resistance to fatigue