Physiology HW 9

Place the following excitation-contraction coupling events in the order that they occur.

1. End-plate potential reaches threshold 2. Action potential sent throughout the sarcolemma 3. Voltage-sensitive DPH receptors are activated 4. Conformational change opens RyR1 channels 5. Release of calcium into sarcoplasm

Thin filaments connect to and extend from either side of a ___________. These thin filaments are composed largely of the myofilament ____________.

z disc; actin (Recall that Z discs form the boundary of each individual sarcomere, and that multiple, thin, actin filaments extend perpendicularly from each Z disc.)

What happens to the amount of plasma-free fatty acids used for energy as exercise continues?

They increase, as stored adipose tissue is hydrolyzed for energy.

Hundreds of mutations have been identified in RyR1 that contribute to multiple muscular diseases. Assume that a new mutation was discovered that causes this receptor to continually remain open. Based on what you know about the function of this receptor, how would you expect this new mutation to impact contraction?

This mutation will increase levels of calcium in the sarcoplasm, which will induce continued muscle contraction. (Recall that when activated, RyR1 allows an efflux of calcium from the sarcoplasmic reticulum into the sarcoplasm.)

Rigor mortis occurs after death because ____________________.

detachment of crossbridges does not occur due to the lack of ATP (Recall that the myosin head binds ATP, which causes it to detach from actin. Myosin subsequently hydrolyzes the molecule of ATP, which reenergizes the myosin head so that it is ready for future contraction.)

The presence of calcium in the sarcoplasm is directly responsible for ____________________.

exposing the binding sites on actin (Recall that the binding of calcium to troponin causes a conformational change in the troponin-tropomyosin complex associated with the actin myofilament. This exposes the myosin binding sites on actin.)

If it were possible to move the terminal cisternae further away from the T-tubules, it would ____________________________.

interfere with the signal required for the release of calcium from the sarcoplasmic reticulum (Recall that the DHP receptor and RyR1 are tightly coupled and that the transfer of the signal from the T-tubules to the SR depends upon the allosteric interaction between each of these receptors.)

Acetylcholine causes an end-plate potential by triggering the ______________________.

opening of sodium channels (Recall that an end-plate potential is a local depolarization due to the influx of sodium.)

Check all the characteristic of cardiac muscle tissue.

-Cells are striated -Gap junctions join adjacent cells -Under autonomic control (Cardiac muscle cells are striated, like skeletal muscle cells. However, unlike skeletal muscle cells, which are separated from one another, cardiac muscle cells are connected by gap junctions.Cardiac muscle cells are striated, like skeletal muscle cells. However, unlike skeletal muscle cells, which are separated from one another, cardiac muscle cells are connected by gap junctions.Cardiac muscle cells are striated, like skeletal muscle cells. However, unlike skeletal muscle cells, which are separated from one another, cardiac muscle cells are connected by gap junctions.Cardiac muscle cells are striated, like skeletal muscle cells. However, unlike skeletal muscle cells, which are separated from one another, cardiac muscle cells are connected by gap junctions.)

The correct sequence for smooth muscle contraction is:

1. calcium released into cytosol 2. calcium binds to calmodulin in cytosol 3. calcium-calmodulin complex binds with myosin light-chain kinase 4. ATP used to phosphorylate myosin cross bridges 5. phosphorylated cross bridges bind to actin filaments

The correct sequence for skeletal muscle contraction is:

1. increased levels of calcium in the cytosol 2. calcium binds to troponin 3. tropomyosin shifts, exposing active sites 4. myosin forms cross bridge with actin

Myosin heads directly use ______________ to transition to their _____________________ conformation, which enables them ready to bind to actin.

ATP; energized ( Recall that the hydrolysis of ATP causes a conformational change in myosin heads, which energizes them in preparation for contraction.)

Acetylcholine (ACh) is released from motor neurons and enters the __________________.

synaptic cleft (Recall that ACh-filled synaptic vesicles are released from the axon terminal, and they subsequently diffuse across the synaptic cleft.)