Muscle Anatomy
What are thin filaments?
actin, troponin, tropomyosin
peri
around, wraps around each fascicle (collagen and elastic fibers)
what do you have to wait for to bind?
calcium without the cycle will not start
skeletal muscle tissue
cells are long, cylindrical, striated, and multinucleate
cardiac muscle tissue
cells are short, branched, and striated, usually with a single nucleus; cells are interconnected by intercalated discs
function of cardiac muscle
circulates blood; maintains blood (hydrostatic) pressure
what happens to smooth muscle during contraction?
contracts from both sides when both ends are free to move, the ends of a contracting muscle fiber move toward the center of the muscle fiber
what happens to skeletal muscle during contraction?
contracts from one side, when one end of a myofibril is fixed in position the free end is pulled toward the fixed end (origin is usually the fixed portion, insertion is moveable portion)
a band
dark area; extends length of the thick filaments
What is titin?
elastic protein, keeps thick and thin filaments aligned
high energy myosin
head attaches to thin filament, ADP and P bound to myosin, high affinity for actin
endo
inside, wraps around each fiber
M line
middle of sarcomere
functions of smooth muscle
moves food, urine, and reproductive tract secretions; controls diameter of respiratory passageways; regulates diameter of blood vessels
Functions of skeletal muscle
moves or stabilizes the position of the skeleton; guards entrances and exits to the digestive, respiratory and urinary tracts; generates heat; protect internal organs
What happens to the H zone during contraction?
muscles shorten/ disappears
what are thick filaments?
myosin
what is the moving active component in cross bridge?
myosin head
what filaments shorten?
neither
what do the thick and filaments do?
overlap
what is muscle contraction?
shortening of muscle
what happens to the I band during contraction?
shortens
What are the three types of muscle tissue?
skeletal, cardiac, smooth
during excerise blood flow shifts from the GI tract to skeletal muscle as a result of increased oxygen demand. Which muscle type is mainly responsible for redirecting blood flow?
smooth
What happens to the A band during contraction?
stays the same
if we do not have atp what happens
the myosin and actin become locked in position
I band
thin filaments only
calcium binds to ___ during cross-bridge cycle
troponin
epi-
upon; silver skin around the entire muscle (dense irregular CT)
sarcomere
what is this image of?
does the contraction cycle repeat?
yes, cycle repeats while Ca 2+ is high and ATP is available
when does the stimulus end?
- SR calcium channels close - calcium ion pumps return Ca2+ into terminal cisternae (SR) - Troponin- tropomyosin complex resumes original position, covering active sites, blocking new cross-bridge formation
step 3 of muscle fiber contraction
- active sites exposed - calcium binds to troponin - troponin changes positon, moves tropomyosin and exposes active sites on actin
step 2 of muscle fiber contraction
- contraction cycle begins - calcium ions arrive from sarcoplasmic reticulum
step 4 of muscle fiber contraction
- cross bridges form - myosin heads bind to exposed active sites on actin - forms cross-bridges
step 6 of muscle fiber contraction
- cross-bridge detach - a new ATP attaches to each myosin head, myosin releases from actin - active site available to form another cross-bridge
step 5 of muscle fiber contraction
- myosin heads pivot - cross-bridge formation causes myosin heads to pivot toward M line (center sarcomere) - ADP and P release
step 7 of muscle fiber contraction
- myosin reactivates - free myosin head splits ATP and ADP and phosphate - released energy used to "recock" myosin head
step 1 of muscle fiber contraction
- resting sarcomere - myosin heads are all "energized" and "cocked" - cocking head requires breakdown of ATP - myosin head acts as ATPase; ADP and P stay attached to head
which about sarcomere shortening is true?
- the thick and thin filaments slide past each other - the length of the A band remains constant - the H zone almost disappears
what is the contraction cycle?
1. contraction cycle begins 2. active- site exposure 3. Cross Bridge formation (myosin binds to actin) 4. Myosin head pivoting (power stroke) 5. cross-bridge detachment 6. myosin reactivation
Z line
A dark thin protein band to which actin filaments are attached in a striated muscle fiber, marking the boundaries between adjacent sarcomeres. (ends of sarcomere)
what is crucial for myosin?
ATP
low energy myosin
ATP bound to myosin, low affinity for actin
Myosin Head Pivoting
After cross-bridge formation, the energy that was stored in the resting state is released as the myosin head pivots toward the M line. This action is called the power stroke; when it occurs, the bound ADP and phosphate group are released.
smooth muscle tissue
Cells are short and spindle shaped Can divide and regenerate Nonstriated
What is the cross bridge cycle?
It is the cycle in which an energized myosin head binds to actin and performs a power stroke, then binds to ATP in order to detach and re-energize.
H zone
The region at the center of an A band of a sarcomere that is made up of myosin only. The H zone gets shorter (and may disappear) during muscle contraction. only thick filaments