Question

When using your arms to lower yourself into a chair, you bend your arms without using your biceps. Explain how this is possible. (Hint: Think about gravity as an antagonistic force.)

Short answer

When you grab the chair's sides, you are contracting your triceps to maintain your arms extended against the force of gravity on your torso so that the number of motor units is contracted in the triceps decreases.

Step-by-step solution

Skeletal system transform the muscle contraction into locomotion

Converting muscular contraction to movement necessitates using a skeleton, which is a rigid structure to which muscles can adhere. By flexing muscles that connect two elements of an animal's skeleton, it can modify its shape or location.

Muscles are frequently linked to bone indirectly through connective tissue that forms a tendon.

Antagonistic force in muscles

Muscles only exert force when they contract. Therefore, moving a bodily component back and forth often necessitates using two muscles linked to the same piece of the skeleton.An arrangement like the skeleton is found in the upper section of a human arm or grasshopper leg.

Although these muscles appear to be hostile, their function is cooperative and is regulated by the nervous system. For example, when a human extends their arm, motor neurons cause the triceps muscle to contract, whereas the biceps muscle relaxes without neural input.

Bending the arms on the chair without using the biceps

A motor unit comprises a single motor neuron and all of the muscle fibers that it regulates when a motor neuron generates an action potential. All of the muscle fibers in its motor unit contract as one.

The strength of the following contraction is determined by the number of muscle fibers controlled by the motor neuron.When we grab the chair's sides, we contract the triceps to maintain the arms extended against the force of gravity on the torso.

As we progressively lower down into the chair, the number of motor units contracted in the triceps decreases. As we are no longer battling gravity, contracting the biceps will jerk them down.