Lecture 4 - Skeletal Muscle Contraction Flashcards
What is connective tissues surrounding the entire muscle?
Epimysium
What is made up of multiple fascicles?
Muscle
What is connective tissue surrounding individual fascicle?
Perimysium
What is a bundle of myofibers?
Fascicle
What is delicate connective tissue around each myofiber?
Edomysium
What is the cell membrane of each muscle fiber called?
Sarcolemma (=plasmalemma)
What is an individual multinucleated muscle cell called?
Myofiber
What is a chain of sarcomeres within a myofiber?
Myofibril
What is actin and myosin filaments that make up a sarcomere called?
Myofilament
What anchor actin filaments and are located at the end of a sarcomere?
Z discs (Z lines)
What are composed entirely of actin and change their width during contraction?
I bands
What are composed of actin and myosin and do not change their width during contraction?
A bands
What are composed entirely of myosin and change their widths during contraction?
H bands
What are responsible for the banding pattern characteristic of striated muscle?
Sarcomeres alignment
Describe the sequences LEADING UP TO the sliding filament mechanism.
1) Action potential arrives
2) Voltage gated calcium channels open
3) Ach released into synaptic cleft
4) Opening of ligand gated sodium channels
5) Action potential occurs
6) Voltage gated T-tubules interact with ryanodine receptors on SR membrane
7) Opening of Ryanodine-sensitive calcium ion release channels
8) Ca2+ increases in cytosol
9) activation of sliding filament mechanism
Describe the sequences after Calcium has been released in the cytosol to muscle contraction.
1) Calcium ions bind to troponin
2) Tropomyosin uncovers myosin binding sites on actin.
3) ATPase heads of myosin molecules split ATP and bind to actin.
4) Stored energy in myosin head causes deformation such that thick and thin filaments slide past one another.
5) A second ATP binds to myosin and causes it to release actin
6) process is repeated
7) contraction stops when ATP-dependent calcium pump sequesters calcium ions into SR.
What causes conformational changes in the ryanodine receptors and are located on the sacrolemma T-tubules?
Dihydropyridine receptors (DHP)
What open in response to conformational changes in the DHP receptors and allow calcium to flow into the cytosol from the SR?
Ryanodine receptors (RyRs or Ca2+ release channels)
How many heads does each myosin molecule contain?
2
Where is ATP required for muscle contraction? (3)
1) sliding filament mechanism (most)
2) pumping calcium from sarcoplasm back into SR
3) pumping sodium and potassium ions through the sarcolemma to reestablish resting potential.
What type of contraction occurs when there is an increase in tension but not in length?
Isometric
What type of contraction occurs when there is a change in muscle length? (2)
Isotonic contraction. Eccentric - lengthens, Concentric - shortens.
What type of muscle has fewer mitochondria, primarily uses anaerobic respiration, and has a larger concentration of ATPase?
Fast(white), contract rapidly but have less endurance. Example: gastrocnemius
What type of muscle has more mitochondria, primarily uses aerobic respiration, has more myoglobin, and smaller concentration of ATPase?
Slow(red), slow twitch fibers contract more slowly but have more endurance. Example: soleus
