Final-Chapter 11 Muscle Physiology Flashcards Preview

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Flashcards in Final-Chapter 11 Muscle Physiology Deck (15):
1

How is muscle contraction terminated?

Motor neuron input terminates or stops released of ACh. The motor neuron is part of PNS, carries electrical signal from brain to arm, stops receiving ACh, tells arm to stop contracting.
1. EPPs terminate meaning no more ACH is binding to receptors and SR has a ton of calcium in side.
2. High myoplasmic calcium concentration shuts SR calcium channels which means no more Ca coming out of SR channels, but still a lot more Ca in the SR than the cell.
3. Active calcium uptake through SERCA pumps on SR. Uses ATP to pump Ca against its gradient from the sarcoplasm [low] to the SR [high]. Pumps it back into the SR, from low to high concentration.
4. Calcium dissociates from troponin.
5. Tropomyosin covers myosin binding sites on actin. Myosin and actin can’t interact, no crossbridge, no muscle contraction.
6. Sarcoplasm reticulum has a ton of calcium inside of it. To get Ca against concentration you use ATP for the SERCA pumps. When Ca levels get lower in the cell, you have no more Ca binding to tropomyosin. Myosin and actin cannot interact and you get no muscle contraction which means no crossbridge interaction.

2

What is the twitch?

The twitch is the mechanical response or change in force/tension (measured in grams) of an individual muscle fiber, motor unit, or whole muscle to a single action potential. Individual muscle contraction, for a single muscle fiber which results from a single AP, generally a very small AP and do not serve much purpose. You normally need several to get a huge muscle contraction to actually do work. There are two types of twitches Isometric and Isotonic.

3

What is the difference between a isometric twitch and an isotonic twitch.

Isotonic twitch occurs then muscle generated force causes muscle shortening and lifts a load [load must be less than or equal to muscle tension. What you would generally think of muscle contraction being – allows for lifting weights, i.e. Lifting a weight you CAN move.

An Isometric twitch occurs when muscle generates force but does not shorten [load force opposing muscle shortening greater
than muscle tension]. i.e. Like pushing against a wall – the wall doesn’t move. The force the wall is exerting is less than what you are exerting.

4

What is the difference between a slow twitch and a fast twitch fibers.

Fibers are based on how long after the stimulus it takes for the muscle to respond.
Slow twitch: contain slow myosin, that hydrolyzes ATP to ADP and Pi slower, resulting in myosin head cocking slower. Slow because it breaks down ATP more slowly than fast twitch.
The Fast twitch contains fast myosin that hydrolyzes ATP to ADP and P faster, cocking the myosin head faster. Faster hydrolyzing means faster cross-bridges.
So the difference between fast and slow twitch relies on the amount of time it takes to hydrolyze ATP, and the myosin head. Skeletal muscles can contain slow twitch fibers, fast twitch fibers or mixture of both.

5

What are some examples of the different types of muscles?

1. Extra ocular takes 7-8 sec; this is around your eyes; it faster because it travels a shorter distance.
2. Gastrocnemius takes 40 secs; this is calf muscle.
3. Soleus: 90 msec; this is your heel.

6

What is the main difference between glycolytic and oxidative fibers?

The main difference between glycolytic and oxidative fibers is how much oxygen is available.

7

Describe glycolytic fibers?

Glycolytic fibers are anaerobic they generate more ATP through glycolysis. Glycolytic fibers have high cytosolic concentration of glycolysis enzymes and contain few mitochondria because they don’t’ need them. They are large in diameter and lighter in color because they’re not getting a lot of blood because they don’t need a lot of oxygen. When you eat dark meat, it has high blood flow. Glycolytic is white meat on the chicken.

8

Describe oxidative fibers?

Oxidative fiber are aerobic and generate more ATP through oxidative phosphorylation. Oxidative fibers contain Low concentration of glycolysis enzymes and lots of mitochondria because of Oxidative Phosphorylation. They also possess myoglobin an oxygen storage molecule because it needs oxygen to do work. Myoglobin is just like hemoglobin protein but is found in the muscle. Oxidative fibers have a small diameter surrounded by capillaries and are darker in color.

9

What does low intensity exercise do in muscle fibers?

Low intensity exercise increases oxidative capacity because they are working constantly which Increases size and number of mitochondria, decreases fiber diameter, and increase number of capillaries surrounding fibers. The conversion of some glycolytic fibers into oxidative fibers. If you’re working out all the time but still breathing a lot, your body uses the extra oxygen for the oxidative fibers. The trade off is that you’re not building stamina. You have a ton of fibers that need oxygen because you won’t have a lot of fibers that do not need oxygen.

10

What does high intensity exercise do in muscle fibers?

High intensity exercise increases glycolytic capacity. High intensity exercise increase in glycolysis enzymes (more myofibrils), fiber diameter, and the number of myofibrils. It decreases oxidative capacity and the size and number of mitochondria. The conversion of some Oxidative Fibers into Glycolytic Fibers because you are depriving your body of oxygen. Over time you can run longer and longer without getting tired. They learn to function to make ATP without oxygen which decreases oxidative capacity which means it also decreases size and number of mitochondria.

11

What is muscle fatigue caused by in low and high intensity exercise?

Low intensity exercise (aerobic) fatigue is caused by depletion of energy reserves (glycogen). Where as in high intensity exercise (anaerobic) fatigue is caused by lactic acid buildup. Very high intensity exercise causes depletion of ACh resulting in neuromuscular fatigue. Endorphins are nature’s pain killers. They are released when runners experience runner’s highs.

12

What are the types of muscles?

Skeletal are striated and voluntary.
Cardiac muscles are striated and involuntary. Smooth muscles are non-striated.

13

Describe the smooth muscle anatomy?

Smooth muscles have no striations meaning no sarcomeres [stripes], hence the smooth description. Instead of actin and myosin sliding on top of each other, they crisscross throughout the entire muscle cell. Actin and myosin run parallel to each other in several axes (contractions still occur through crossbridge cycling). Actin and myosin connect to connective tissue at dense bodies. One difference between skeletal muscle contraction and smooth muscle contraction is the source of the calcium. All muscle contraction requires calcium to contract. Skeletal muscle – internal Ca2+ form SR and Smooth Muscle Calcium comes mostly from external Ca2+ entering the muscle cell.

14

How is smooth muscles excited?

Most Ca for smooth muscle contraction comes from outside the cell. But some from the ER and if this happens, you get a signal transduction pathway. If Ca enters from outside: Ca levels increase in the cell. The first thing Ca does is bind to calmodulin which makes Ca-calmodulin. Ca-calmodulin activates MLCK (myosin light chain kinase), another enzyme. All kinases do the same thing, they phosphorylate. MLCK phosphorylates the myosin light chain. The myosin light chain is now active and can get cross bridge formation which activates ATPase, forms crossbridges, and causes muscle to contract.

15

How do you shut off smooth muscle contraction?

Inactivation of myosin by phosphatases (enzyme, opposite of kinase), which remove phosphate group from myosin light chain which then shuts off smooth muscle contraction.