BY 30 – Fall 2001
16.1. Skeletal
Muscle Contraction
a. The _________________________ model proposes that muscle contraction occurs by ________________________ and __________________________ sliding past one another. Specifically, the _______________________ heads attach to __________________________ and pull them toward the middle of the _______________________.
b. During muscle contraction, the __________________________ approach one another and the __________________________ shortens.
c. Because the mysosin heads have the ability to hydrolyze ATP, they are said to have _____________________ activity. When they bind ATP and hydrolyze it, this allows the __________________________ myosin head to attach to _____________________________.
d. The power stroke of the cross-bridge cycle involves movement of the ______________________ toward the center of the _____________________ which causes the __________________________ to move. At this point both ________________________ and _________________________ are released from the myosin head.
e. To detach the myosin head from _____________________, another molecule of _____________________ must bind to myosin. In the condition known as _______________________________, there is no ATP available such that the ____________________ remain attached to actin producing muscle stiffness.
f. Provided that enough ATP is available, muscle contraction takes place as the intracellular concentration of ___________________ increases. The sequence of events between neural stimulation and muscle contraction is referred to as ______________________________ coupling.
g. At the neuromuscular junction, acetylcholine (ACh) binds to a _________________ ACh receptors located on the _____________________ plate. As a result of binding, _____________________ enters the muscle cell and __________________________ leaves the cell, but the net result is an _____________________________ which brings the muscle cell to threshold generating an action potential.
h. The action potential travels along the sarcolemma and down ______________ tubules which causes Ca2+ to be released from the ______________________. The Ca2+ in turn binds to _________________________________ causing the _________________________ to move, thereby exposing the myosin binding site on _________________________. This allows cross bridge formation to take place.
i. Contraction is terminated as Ca2+ is pumped back into the ________________ by the action of the __________________________. Within the SR, Ca2+ binds to a protein called _______________________.
16.2. Skeletal
Muscle Mechanics
a. As a result of cross-bridge cycling, a muscle generates _________________, but may or may not ____________________________ depending on the load that it must move. Contractions which involve no shortening are called ______________________ while contractions in which the muscle shortens are called ________________________. Nevertheless, in an isometric contraction, cross-bridges do continue to _______________________, but they don’t move the __________________________.
b. The mechanical response of a muscle fiber to a single action potential is called a ______________________.
c. An isometeric twitch can be subdivided into the _________________________ period, which is the time involved with _______________________________; the _______________________ phase, which is the time interval from onset of conctraction to _______________________; and the _____________________ phase, which is where _________________________ decreases.
d. Because the action potential duration is only about __________________ msec and the twitch lasts for about _____________________ msec, it is possible for a second action potential to arrive during the mechanical response giving rise to __________________________, which involves an increase in the mechanical response of the muscle fiber to successive ___________________________.
e. As the frequency of action potentials increases, the level of sustained tension reaches a maximum, a state known as ______________________, which can be described as ____________________ when tension oscillates because of partial relaxation, or __________________________ in the absence of oscillation. The maximum tension is about _________________ times higher than twitch tension.
f. The amount of tension generated by a muscle fiber can be altered by changing it’s __________________ before contraction. The ______________________ length is defined as the length at which the fiber develops maximum tension, the explanation being that this length maximizes ______________________ interactions.
g. The muscles, bones, and joints of the body are arranged as ________________ systems. To maintain mechanical equilibrium we can calculate the force a muscle must exert (F1) if we know the distance between the joint axis and its attachment (D1); the load (F2); and the distance between the joint axis and the load (D2). The formula which relates these quantities is ______________ x ________________ = _____________ x _______________.
16.3. Skeletal Muscle Metabolism and Fiber Types
a. Muscle cells need large amounts of ATP for such processes involving the ___________________________, ___________________________, and ___________________________.
b. Muscle cells have ATP stores that will last for only a few _______________. Thus they can generate ATP by three processes: _______________________; _________________________; and _______________________________.
c. Creatine is a small amino acid-like molecule that can be converted to ____________________________, which serves as an energy store due to its ability to transfer its ________________________ to ADP when ATP levels become depleted. So at rest, muscle cells make _______________________ whereas during activity, this molecule is converted back to _____________________________. This source of ATP is sufficient for ______________________________ of muscle activity.
d. At moderate levels of muscle activity, most ATP comes from __________________________ involving first ________________________, then fuels carried to muscle within __________________________ (examples are _________________________ and ____________________________).
e. When the intensity of exercise exceeds 70% of maximum, _______________ contributes a significant amount of ATP production. A consequence however is the formation of ______________________.
f. The inability of muscle to contract forcefully after prolonged activity is called ___________________________, which is distinguished from ___________________________ involving the sense of fatigue and the desire to stop exercising. Actual muscle fatigue depends on depletion of ______________________ from the SR; depletion of ___________________ and other nutrients; and the buildup of ____________________________ and _____________________________.
g. The onset of fatigue and its rate of development depend in part on the type of skeletal muscle _____________________, which come in three types called ______________________________, ______________________________, and ___________________________.
h. Fibers known as _____________________ have low ATPase activity and rely on ________________________________ respiration. They also have many _____________________ and abundant amounts of ____________________, which give them a dark-red color – hence these fibers are called ____________________________ muscle. These fibers have the smallest _____________________________ meaning that they develop the least force, but are the most resistant to _______________________.
i. Fibers known as _______________________ have higher ATPase activity but also rely on oxidative respiration. They too have abundant _______________ so that they too are known as _________________________ muscle.
j. Fibers known as ______________________ have the highest ATPase activity, but rely on ______________________________. Because they lack abundant amounts of myoglobin, they are known as ______________________ muscle. These muscle fibers have the largest ______________________ and thus can generate the most _________________________. They are the most prone to _____________________________.
16.4. Cardiac
Muscle
a. Cardiac muscle also possesses _________________________ organized into ________________________ which gives rise to its striated appearance.
b. Like skeletal muscle, cardiac muscle cells possess _______________ tubules; and abundant __________________ and contract by the ________________ model.
c. Unlike skeletal muscle, cardiac muscle cells possess ____________________ nucleus per cell, located _____________________________ of the cell. Also individual fibers are joined at their ends by ___________________________, which include _________________________ (provide mechanical adherance) and _______________________ (provide for intercellular communication).
d. Functionally, certain cardiac muscle cells can spontaneously generate _______________________ giving rise to a phenomena called _____________________________. As a result cardiac muscle is considered to be ____________________ but can be modulated by certain hormones and the ____________________________ nervous system.
e. In response to sympathetic stimulation, both ___________________________ and the ________________________________ will increase. In response to parasympathetic stimulation, _________________________ will decrease.
16.5. Smooth
Muscle
a. Smooth muscle comes in two basic types called _______________________ and _________________________ smooth muscle.
b. In _____________________________ smooth muscle, individual cells have their own ______________________ and so fibers can contract as individual cells. In this type, the number of _____________________________ is low.
c. In _______________________________ smooth muscle, few fibers receive synapses, but the number of _________________________ is high. As a result, a group of cells contracts as a ________________________.
d. Like cardiac muscle cells, smooth muscle cells have ___________________ nucleus per cell, but thick and thin filaments are not organized into _________________________. They also don’t have __________________ tubules.
e. Functionally, certain smooth muscles demonstrate _____________________, and can be modulated hormones and the _______________________ nervous system. But unlike both skeletal and cardiac muscle, Ca2+ binds to _____________________________ which in turn activates an enzyme called _____________________________________. This enzyme phosphorylates ____________________, which allows _____________________________ to form.