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