Rank the motor units in the order of recruitment as increased force is demanded
ID: 167471 • Letter: R
Question
Rank the motor units in the order of recruitment as increased force is demanded of skeletal muscle. a. Type I b. Type IIa c. Type IIb If a muscular contraction requires the recruitment of Type IIb muscle fibers, the force produced will be _____ contraction will be_____ (fast/slow), and the contraction _____ (will/will not) length of time. Adding which of the following solutions to the glycerinated muscle preparation resulted in contraction? (Check all a. ATP only b. salts only c. ATP + salts When the supply of ATP in a muscle runs out, myosin heads remain detached from actin. _____ Put the following phases of a muscle twitch in the correct order. a. period of contraction b. latent period c. period of relaxation Match the description of the stimulus applied to a muscle fiber listed in column A with the corresponding Column A Column B 1. not strong enough to produce a muscle twitch 2. strong enough to produce a muscle twitch but no summation _____ 3. stronger than necessary to cause summation a. subthreshold b. suprathreshold c. thresholdExplanation / Answer
Answer. 14.
Motor unit recruitment depends on force demand. With less force applied, Type I (slow twitch) motor units are recruited. As force demand increases, Type IIa (fast twitch) are recruited, followed by recruitment of Type IIb when the force demand further increases.
Therefore, the order of recruitment is (a), then (b) and finally (c).
Answer. 15.
Type IIb fibers are fast twitch fibers that gives quick, powerful burst of speed. They have the highest rate of contraction among all the other muscle fibers. They also have high rate of becoming fatigue and they dont last long before it needs rest.
So, the answer is
If the muscle contraction requires the recruitment of Type IIb muscle fibers, the force produced will be more, contraction will be fast, and the contarction will not continue for the length of the time.
Answer. 16.
The force of contraction in muscle cell depends on the interaction of Actin and myosin, and the free energy of their interaction is driven by ATP in a glycerinated solution. As the concentration of ATP increases, the isometric tension increases to maximum and decreases to a plateau.
Therefore, the correct answer is (a) ATP only
Answer. 17.
In the presence of ATP and Calcium, the cross bridge formed between Actin and Myosin triggers the contraction. Thus, muscle fibers continue to shorten.
When the muscle fiber runs out of ATP, myosin detaches from actin, thus muscle stops contracting and becomes fatigue.
So the answer is Muscle stops contraction and becomes fatigue.
Answer. 18.
The phases of muscle twitch are divided in 3 phases - (i) Latent period, followed by (ii) Contraction period and finally (iii) Relaxation period.
So the correct order for the phases of muscle twitch is (b), then (a) and finally (c).
Answer 19.
There is no response fromt the muscle below threshold stimulus. At threshold stimuls, only the muscle fibers with lowest threshold responds and contracts. As the stimuls becomes superthreshold, there is increase in number of motor units, resulting in increase of amplititude of stimulus and Summation.
Therefore, the correct match is
1 = a; 2 = c; 3 = b
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