Question

Explain the following using your knowledge of muscle contractions. How is it possible that we can delicately pick up a flower, yet the same muscles can squeeze/crush a pop can? You should discuss motor units/neurons, muscle fibres, frequency (of motor neurons firing = fibre contraction) and the All-or-None Principle.

Answer 1

Muscle contraction occurs when the stimulus reach the neuromuscular junction via neuron. Then acetylcholine is released into the synaptic cleft. The acetylcholine binds to the receptors in the motor end plate which opens the voltage gated Calcium channels. The Ca2+ influx occurs to the sarcoplasmic reticulum which binds to the troponin and removes the troponin blockade on actin. Now the myosin head binds to the actin and there phosphorylation occurs and ATP converts to ADP and the myosin head is activated. The binding of the myosin with the actin form cross bridge. Now muscle contraction occurs. Now the sarcomere length decreases as in a maximal contraction the sacomere length become the most smallest. Then the cross bridge breaks and the acetylcholine is degraded. Troponin blockade comes back to position. Now muscle gets relaxed. It's the basic principle.

Now we need to check about the motor neurone firing. The brain send impulses to the junction. The neurone starts firing in a smallest rate. But to stimulate a contraction the firing should cross the threshold. This is explained by all or none theoy. If there is no firing there is no contraction. If the. Figuring is not above threshold there is no contraction. If. The firing is above threshold there is contraction. Now we need to tell about the motor units. The motor neurones innervates the muscle fibre forms a motor unit. At the lowest firing few motor units gets activated creating a smallest contraction making ourself Abbie to gently pick a flower. But when the neurone fire continuously more motor units gets activated and after the refractory period of the muscle fibre the without getting to the relaxed state this forces the muscle to a strong contraction allowing us to squeeze the flower. This is how muscle contraction works.