(1) The varying number of muscle fibers that contract
<span>In most muscles, the number of muscle fibers in different motor units ranges from a few to hundreds. The nervous system can thus regulate the strength of contraction in a muscle by determining how many motor units are activated at a given instant and by selecting large or small motor unties to activate. </span>
some muscles are almost always partially contracted. In such muscles, the nervous system my alternate activation among the motor units, reducing the length of time any one set of fibers is contracted. Prolonged contraction can result in muscle fatigue due to the depletion of ATP and dissipation of ion gradients required for normal electrical signals.ing.
<span>(2) varying the rate at which muscle fibers are stimulated </span>
<span>single action potential produces a twitch lasting about 100 msec or less. If a second action potential arrives before the muscle fiber has completely relaxed, the two twitches add together, resulting in greater tension. Further summation occurs as the rate of stimulation increases. When the rate is so high that the muscle fiber cannot relax at all between stimuli, the twitches fuse into one smooth, sustained contraction called tetanus.</span>
Answer:
Yes.
Explanation:
As a blood vessel, Superior vena cava carries completely digested substances that is present in the blood from upper part of the body to the heart. Blood is a fluid that transport digested food from small intestine to other parts of the human body. It also carries oxygen from the lungs to the cells and also carries carbondioxide from the cells to lungs so we can say that Superior vena cava carries completely digested materials.
Option C, animals moved from the sea to the land is the right answer.
The Paleozoic Era in the history of the earth was a time of major change on Earth. This was the period that ran about 542 to 251 million years ago. The period commenced with the split of a single super-continent and the development of another. Plants grew extensively. Moreover, the primary vertebral animals conquered the land.
Answer:
herbivore-those kinds of animals that eat plants and trees only e.g elephants
omnivore-those animals that eat both meat and plants e.g baboons /humans
carnivore-those animals that eat meat only some call them the preditors e.g lions /cheetah