Structure of Skeletal Muscle Cells Flashcards
What are the three types of muscle tissue?
Skeletal
Cardiac
Smooth
Skeletal muscle is
attached to bone
striated
voluntary
Cardiac muscle is
found in the heart
striated
involuntary
Smooth muscle
lines hollow organs
non-striated
involuntary
What are the functions of skeletal muscle?
Skeletal movement Maintain posture Support soft tissues Guard entrances/exits Maintain body temp Nutrient Reserves
Define origin
attached to bone, remains relatively stationary during movement
Define insertion:
attached to bone, moves during contraction
Tendons
attach muscle to bone
Define synergistic muscles
muscles work together during a contraction
Define antagonistic muscles
Muscles that oppose each other during a contraction (ex. flexors and extensors)
What is the endomysium
covers individual muscle cells
What is the perimysium
Sheathes bundles of muscle fibers (fascicles)
What is the epimysium
Membrane surrounding a muscle
What is deep fascia
Wrap groups of cooperating muscles together
What connective tissues in skeletal muscles contain blood vessels and nerves?
Endomysium and Perimysium
Describe skeletal muscle cells/fibers
Multinucleate Very long Formed during embryogenesis Adult muscle repair is limited Contains myofilaments
Satellite cells
create new skeletal muscle cells
Actin
thin myofilaments
Myosin
Thick myofilaments
What is the Sarcolemma?
Skeletal cell membrane
____ conduct ation potentials deep into skeletal muscle cells and are close to sarcoplasmic reticulum
Transverse (T) tubules
In skeletal muscle cells action potentials are propogated
perpendicular to surface via t tubules
Sarcoplasmic reticulum stores a high concentration of _____ ions needed for muscle contraction
Ca2+
What excites the SR and tells it to release calcium?
T-tubules
Describe myofibrils
Bundles of myofilaments
Can actively shorten
Anchored to inner surface of sarcolemma at each end of the cell
What is a sarcomere
repeating units of myofilaments in myofibril
Sarcomeres are where we actually have contraction where
thick and thin myofilaments are overlapping
_____ gives banded appearance
differences in distribution of thick and thin myofilaments
I bands
Light band
Contains only thin filaments
A bands
Dark band
contains thick filaments and some overlap with thin filaments
____ band contains only thick filaments
H bands
What is the Z disk?
Border between sarcomeres
Muscles shorten during contraction because
The myosin and actin filaments slide between each other to shorten each sarcomere
As thin filaments move toward center of sarcomere
Thin filaments slide over thick
Z lines pull close together
I bands and H band narrow
A band stays same width
When is a sarcomere at maximum shortening?
When its the width of the A band, no I band or H band are visible
Where do cross bridges form?
Myosin filaments have short projections that bind to sites on actin filaments
_____ use ATP to change shape and pull the actin and convert chemical energy to mechanical energy
Cross bridges
What part of myofilaments form cross bridges during contraction?
Globular heads
Interactions between myosin head and actin prevented by ____ during rest
tropomyosin
Which type of myofilament has an actin active site that are covered by tropomyosin during rest?
Thin myofilaments
What is the sliding filament theory?
- Calcium released from SR
- Calcium binds to troponin
- Troponin moves
- tropomyosin moves
- Actin Active sites exposed
- Cross bridge forms
- ATP allows release of cross bridge.
What is the role of ATP in the molecular mechanism of contraction?
- Supplies energy to move the myosin head
- Binds to un-energized myosin head
______ re energizes myosin head
hydrolysis of ADP to ATP
_____ causes crossbridge release
Binding ATP to myosin head
What ion concentration around the sarcomere controls sarcomere contraction?
Ca2+
When calcium ion levels fall
tropomyosin covers actin active sites and ends contraction
