Muscle IV Flashcards
Force generated by a muscle is called […]
Tension
The tension exerted by a whole muscle is controlled by […] and […]
Recruitment, summation
What is recruitment?
An increase in the number of active muscle fibers to generate muscle tension.
What is summation?
It is the additive effects of several closely spaced twitches to generate muscle tension.
Explain summation in the muscle fiber when it gets stimulated at a regular, relatively large interval.
Unfused tetanus occurs - each stimulation will cause a twitch, and the twitches will build on each other such that the fiber will reach a steady state of oscillation between contraction and relaxation.
Explain summation in the muscle fiber when it gets stimulated repeatedly at a very short interval.
Fused tetanus occurs - each stimulation will cause a twitch, and the twitches are so close together that the muscle fiber will just remain contracted.
Tetanus is defined as […]
The sustained contraction of the muscle fiber.
Compare the amount of tension generated by a twitch to the tension generated by unfused tetanus.
The peaks of the unfused tenanus consist of twice as much force as a twitch.
Compare the amount of tension generated by a twitch to the tension generated by fused tetanus.
The tension of fused tetanus is three times the tension of a twitch.
Describe how recruitment works (in general) in the generation of muscle force.
To increase the amount of force being generated by a single muscle, the number of muscle fibers that contract can be increased according to the motor unit of the muscle group.
Explain how the motor unit of the muscle group affects recruitment.
The motor unit, which can be small for something like the eye or large for something like the leg, determines the steps by which recruitment can occur. So a smaller motor unit means more fine-tuned adjustments, while a larger motor unit means more large-scale adjustments.
What is the main energy source for skeletal muscle metabolism?
ATP
Explain the first step of skeletal muscle metabolism.
The muscle has a stock of ATP, which gets converted into ADP when used. But since ATP concentrations have to remain high for the muscle to contract, the existing ATP is just enough to give the muscle time to start generating more elsewhere.
Explain the second step of skeletal muscle metabolism.
The muscle has a stock of creatine phosphate, which can take its phosphate and attach it to the ADP from step 1 to make more ATP using the enzyme creatine kinase. This converts the creatine phosphate to creatine and gives the muscle enough time for other energy-generating mechanisms to come in.
What are the two possible forms of ATP production in skeletal muscle excluding creatine phosphate?
Glycolysis and oxidative phosphorylation
How does glycolysis work in muscle cells?
Muscles can use either glucose from the blood or glycogen from the muscle itself to generate ATP (and pyruvate + lactic acid).
How does oxidative phosphorylation work in muscle cells?
The pyruvate producted by glycolysis can be used to produce more energy.
What are the 3 types of skeletal muscle fibers?
Fast glycolytic fibers, slow oxidative fibers, and fast oxidative fibers.
Describe the characteristics of fast glycolytic fibers in terms of ATPase activity, myoglobin/colour, and amount of force/unit time
High ATPase activity, no myoglobin (white muscle), generates large force over short time period.
Describe the characteristics of slow oxidative fibers in terms of ATPase activity, myoglobin/colour, and amount of force/unit time
Low ATPase activity, presence of myoglobin (red muscle), generates low levels of force over long periods of time.
Describe the characteristics of fast oxidative fibers as they compare to the two other types of skeletal muscle.
The have intermediate properties and use oxidative metabolism.
What is the difference between fast myosin and slow myosin? How does it affect muscle fiber activity?
Fast myosin can cycle through cross bridges very quickly and can therefore generate large amounts of force while consuming ATP very quickly. Slow myosin consumes ATP more slowly and don’t generate as much force, but can sustain contractions for a long period of time.
Which types of skeletal muscle fibers use fast myosin vs slow myosin?
Fast: fast glycolytic fibers, fast oxidative fibers
Slow: slow oxidative fibers
What is the major energy-generating mechanism of fast glycolytic fibers?
Glycolysis
What is the source of glucose for glycolysis in fast glycolytic fibers? Why?
Glycogen in the cell, as it does not have time to retrieve glucose from the blood.
Aside from energy, what is the major output of glycolysis in fast glycolytic fibres? Explain how it gets generated.
Because there’s no oxidative phosphorylation mechanism, the pyruvate generated by glycolysis gets converted into lactic acid.
Explain the function of lactic acid in fast glycolytic fibers.
Lactic acid builds up as the muscle is used, which causes the pH of the muscle fiber to drop. There are many proteins in the muscle that are designed to operate in a narrow pH range, so the muscle stops being able to contract. That’s why the muscle fatigues. This is a safeguard, as it causes the muscle fiber to fatigue before the concentrations of ATP start to get depleted.
How do concentrations of ATP change in the muscle when it is intensely used?
The concentrations of ATP never significantly change and always remain stable.
What is the major energy-generating mechanism of slow oxidative fibers?
Glycolysis and oxidative phosphorylation.
What is the source of glucose in slow oxidative fibers?
Both glycogen from the muscle fiber and glucose from the blood.
Aside from glucose, what are the 2 major inputs for the energy generation process in slow oxidative fibers? Explain what they are used for.
Oxygen and fatty acids. They are both used in the oxidative phosphorylation process.
What is the role of myoglobin in slow oxidative fibers?
It transports oxygen from the blood into the fiber for oxidative phosphorylation.
What are the major outputs in the metabolism of slow oxidative fibers?
Just ATP produced by both glycolysis and oxidative phophorylation.
Describe the energy generation mechanism of fast oxidative fibers.
They have all the same processes as slow oxidative fibers (oxidative phosphorylation). They just have fast myosin instead of slow myosin.
What is the purpose of muscle fatigue?
To protect muscle from damage.
What is the cause of muscle fatigue in response to high-intensity, short-duration activity?
Changes in ion gradients (such as increase in extracellular K+) and reduction in pH due to buildup of lactic acid
What is the cause of muscle fatigue in response to low-intensity, long-duration activity?
Depletion of glycogen
What is the influence of ATP stocks on muscle fatigue?
There is no effect, as ATP does not deplete and the concentrations remain stable.
Describe the changes in muscle physiology that can be expected after low-intensity, long-duration exercise.
This will cause an increase in fiber mitochondria, increased vascularization, and increased ability of muscle fibers to extract ATP energy through oxidative metabolism.
Describe the changes in muscle physiology that can be expected after high-intensity, short-duration exercise.
This will cause an increase in the diameter of fast glycolytic fibers and muscle hypertrophy.
What is the cause of muscle soreness after exercise?
It is due to inflammation in response to muscle damage
Physiological muscles changes in response to exercise are caused by the release of […], such as […]
Factors released by damaged tissue, such as growth factor 1.
What do skeletal and smooth muscle have in common in terms of structure?
They both have myosin thick filaments and thin actin filaments whose interaction causes muscle contraction.
Describe how the structure of smooth muscle differs from that of skeletal muscle (3 ways).
- The arrangement is far less predictable than skeletal muscle, with the thick filaments and thin filaments distributed more haphazardly.
- No striations
- The shape is less fiber-like and more cell-like, and it contracts in a non-uniform manner.
Smooth muscle contraction is activated by […]
Ca2+
Where does the Ca2+ that drives smooth muscle contract come from?
It can come either from the sarcoplasmic reticulum in the cell or from outside the cell.
Describe the steps by which smooth muscle gets activated.
When Ca2+ flows into the cell, it binds to calmodulin, which activates myosin light chain kinase. The kinase phosphorylates and thus activates smooth muscle myosin.
What types of signals regulate the activity of smooth muscle?
Hormones and neurotransmitters of the autonomic nervous system.
