Muscular Tissue Chapter 10 Flashcards
Explain the arrangement of filaments within a sarcomere.
From Z disc to Z disc exists a sarcomere. The dark A band is in the middle which includes the entire length of the thick filament, with the overlapping thin filament. The two I bands on each side of the A band consist only of thin filament. The Z disc is in the middle of an I band. There are two zones of overlap. The H zone is in the middle and only includes the thick filament. The M line is a group of proteins in the dead center of the sarcomere providing structure to the thick filaments.
What is the structure and function of myosin?
Myosin is one of the two contractile proteins. It is referred to as the “thick” filament. Around 300 molecules make up one thread of myosin. Myosin has an elongated tail and two myosin heads. Myosin extends to the 6 surrounding thin filaments.
What is the structure and function of actin?
Actin is the second contractile protein. It is referred to as the “thin” filament. Thin filaments are connected to Z discs. It is twisted into a helix. Each actin molecule has a bonding site for a myosin head.
What are the two regulatory proteins in the thin filaments and what do they do?
Tropomyosin and troponin. In a relaxed state, the actin binding spot is covered by tropomyosin strands. The troponin holds the tropomyosin strand in place. Once Ca2+ is released, it binds to the troponin, causing a conformational change, allowing the myosin head to attach to the free actin binding spot.
Describe the lengths of the thick and thin filaments and the sarcomere as muscle contraction occurs.
The thick and thin filaments do not change length. The sarcomere does decrease in length, overall decreasing the length of the muscle fiber.
What are the four steps to the contraction cycle and describe what they do.
ATP hydrolysis - the myosin head contains an ATP binding spot and an ATP enzyme that hydrolyzes the ATP into ADP and a phosphate group. The reaction taking place is what makes the myosin head move. Remember that the ADP and phosphate group are still attached to the myosin head.
Attachment - the active myosin head attaches to the free actin binding spot and releases the phosphate group. When myosin and actin are connected, it is called a crossbridge.
Power stroke - after the crossbridges form, the bonding site of the ADP opens, the ADP is released, and the crossbridge rotates. The thin filaments are then pulled to the M line.
Detachment - the crossbridge remains attached until another ATP binds to the myosin head.
What is excitation contraction coupling?
The process of an action potential sweeping down the sarcolemma and into the t-tubules causing a release of Ca2+ near the filaments which then cause troponin to change shape, altering the tropomyosin strand to move away from the binding site. A myosin head then takes the free binding spot of the actin molecule and causes a crossbridge to form. The the contraction cycle occurs.
Where are Ca2+ active transport pumps found and what do they do?
They are found on the SR membrane and they use ATP to bring Ca2+ ions back into the SR. During action potentials, there are open channels and more Ca2+ flows out than is pumped back in. Once the action potentials are completed, the channels close and the active transport pumps keep pulling in Ca2+ back in.
Describe the length-tension relationship in terms of 3 examples.
When the length of the muscle is too short, the thin filaments slide past one another and mess up sarcomeric structure. When the length of the muscle is too long, the thin and thick filaments cannot form crossbridges.
The optimal length for force generation is where all of the myosin heads bind to actin receptors without having the thin filaments slide past one another.
Describe how a nerve impulse propagates an action potential in the muscle.
ACh is released into the synaptic cleft, and binds to the receptors that are located on the motor end plate. The receptors then cause Na+ channels to open up and Na+ flows in. This causes an action potential and then travels through the T-tubules and causes the SR to release Ca2+, which then begins muscle contraction. AChE is waiting in the matrix to break down ACh into acetyl and choline.
What do pesticides, curare, and tetanus do?
Pesticides often contain chemicals that block AChE, which causes a rigid paralysis and suffocation.
Curare inhibits ACh receptors, making the muscles feel extremely relaxed, and causes a flaccid paralysis.
Tetanus (clostridium bacteria) is a spastic rigid paralysis that blocks inhibitory transmitters and overstimulates the muscles.
What are the three ways that muscle cells make ATP?
With creatine phosphate, anaerobic cellular respiration ad aerobic cellular respiration.
Explain creatine and its role.
When muscle fibers are relaxed, there are always extra ATP molecules. The enzyme creatine kinase takes those extra ATPs, catalyzes the transfer of a phosphate group of ATP, and produces creatine phosphate and ADP.
When ADP molecules start to increase, the creatine phosphate is then converted back to creatine and ATP. Together, creatine and ATP can provide maximal contraction for approx. 15 seconds.
Explain anaerobic respiration.
Glucose is in the bloodstream and can easily diffuse into a muscle cell. Also, a muscle fiber breaks down glycogen into glucose. This glucose is then broken down to 2 molecules pyruvic acid. This process is called glycolysis. This process takes 2 ATP molecules but spits out 4 ATP molecules. Because there is not enough oxygen, pyruvic acid is converted into lactic acid. About 80% of the lactic acid is sent to the bloodstream. The liver then converts the lactic acid back into glucose. Anaerobic respiration can provide 30-40 seconds of maximal contraction.
Explain aerobic respiration.
One molecule of glucose is broken down to 2 molecules of pyruvic acid. This pyruvic acid is then taken to the mitochondria where oxygen should be plentiful. Aerobic cellular respiration then occurs and one molecule of glucose can produce 36 ATP, while one molecule of a fatty acid can produce 100 ATP.
