Chapter 10 Homework
Define a motor unit.
A motor neuron together with the muscle fibers (cells) it stimulates.
How do muscle cells use ATP?
A huge amount of ATP is needed to power the contraction cycle, to pump calcium into the sarcoplasmic reticulum, and for other metabolic reactions involved in muscle contraction. However, the ATP present inside muscle fibers is enough to power contraction for only a few seconds. If muscle contractions continue past that time, the muscle fibers must make more ATP. Muscle fibers have three ways to produce ATP: (1) from creatine phosphate, (2) by anaerobic cellular respiration, and (3) by aerobic cellular respiration. The use of creatine phosphate for ATP production is unique to muscle fibers, but all body cells make ATP by the reactions of anaerobic and aerobic cellular respiration.
Define a neuromuscular function.
A synapse between the axon terminals of a motor neuron and the sarcolemma of a muscle fiber (cell).
What is the function of acetylcholine?
It is the neurotransmitter released at the NMJ.
Describe the motor unit differences between muscles with fine control, like the hands, and muscles like the quadriceps.
Muscles involved with fine control have small motor units while those moving large body parts, such as the quadriceps, have large motor units.
Describe actin and myosin filament functions.
Myosin is a contractile protein that makes up thick filament; molecule consists of a tail and two myosin heads, which bind to myosin-binding sites on actin molecules of thin filament during muscle contraction. Actin is a contractile protein that is the main component of thin filament; each actin molecule has a myosin-binding site where myosin head of thick filament binds during muscle contraction.
Define muscle fatigue.
Inability to maintain force caused by insufficient oxygen, lack of glycogen, increased fermentation, and ionic imbalance.
Once an action potential goes down a T-tubule, what affect does it have on the terminal cisterns of the sarcoplasmic reticulum?
It causes changes in the terminal cisterns of the sarcoplasmic reticulum.
Describe the role of creatine phosphate (phophogen system) with regard to ATP regeneration.
Most of the excess ATP is used to synthesize creatine phosphate, an energy-rich molecule that is found in muscle fibers. The enzyme creatine kinase (CK) catalyzes the transfer of one of the high-energy phosphate groups from ATP to creatine, forming creatine phosphate and ADP. Creatine phosphate is three to six times more plentiful than ATP in the sarcoplasm of a relaxes muscle fiber. When contraction begins and the ADP level starts to rise, CK catalyzes the transfer of a high-energy phosphate group from creatine phosphate back to ADP. Since the transformation of ATP from creatine phosphate occurs very rapidly, creatine phosphate is the first source of energy when muscle contraction begins. The other energy-generating mechanisms in a muscle fiber take a relatively longer period of time to produce ATP compared to creatine phosphate. Together, stores of creatine phosphate and ATP provide enough energy for muscles to contract maximally for about 15 seconds.
What is the function of the tropomyosin-troponin complex?
Tropomyosin is a regulatory protein that is a component of thin filament; when skeletal muscle fiber is relaxed, tropomyosin covers myosin-binding sites on actin molecules, thereby preventing myosin from binding to actin. Troponin is a regulatory protein that is a component of thin filament; when calcium ions bind to troponin, it changes shape; this conformational change moves tropomyosin away from myosin-binding sites on actin molecules, and muscle contraction subsequently begins as myosin binds to actin.
