Question

As the resistance (load) to muscle contraction increased, what happened to the velocity of muscle contraction?

a) it increased

b) it stays the same

c) it increased dramatically and then leveled off

d) it decreased

2) how is wave summation achieved in vivo (that is, in the living muscle)?
a) by decreasing the amount of potassium

b) by increasing the strength of a neuron’s action potential

c) by increasing the frequency of neuron firing

d) by myelinated great the neuron

Answer 1

# 1. The answer is option d) it decreased.

  When there is increase in load, the muscle contraction will not be easier as when there is no load of resistance. So when there is a load of resistance to the muscle, this resistance force make it less effective in making the contraction as there is a force which opposes it's action and that will simply decreases the velocity of contraction. The exact opposite will happen when load of resistance is decreased (contraction velocity increases).

# 2. The answer is option c) by increasing the frequency of neuron firing.

Wave summation is achieved when a stimulus is given to the muscle before it's relaxation period which causes a more stronger contraction of the same muscle than it's normal contraction. In this condition, more calcium ions will be released and that will increases the force of contraction by increasing the frequency of motor neuron firing. So the basic mechanism of wave summation is achieved by increasing the frequency of neuron firing. The amount of potassium, strength of a neuron’s action potential and neuron myelination do not have any role in wave summation.