Question

A stronger muscle contraction occurs when the brain _______.
A) Send signals to a larger number of motor units to contract.
B) Activates muscle cells more quickly.
C) Activates the motor units of the muscle one at a time.
D) Sends nerve impulses to the muscle one at a time instead of in bursts.

Answer 1

Hint:
For muscle contraction first of all a neurotransmitter at the motor end-plate. Generation of action potential in muscle fibers. Inward propagation of depolarization along T-tubules. Release of calcium from the sarcoplasmic reticulum. Binding of calcium to troponin C, uncovering myosin binding sites on actin. Then linkages are formed between actin and myosin and sliding of thin on thick filaments.

Complete step by step solution:
Motor neurons, with the help of a rate code signal the amount of force that is to be exerted by a muscle. Increased action potentials with the help of motor neurons cause an increased amount of force that is generated by the motor unit. When the impulse reaches a muscle fiber, it mediates a reaction in each sarcomere between actin and myosin filaments. This helps in the start of contraction and sliding filament theory.
Motor units help in controlling the skeletal muscles and these provide the force for every movement made by us. Like walking, weight lifting, breathing, etc. that is involuntary. The muscle contraction is triggered when action potential travels along the nerves to the muscles. When the nervous system generates a signal then muscle contraction begins. The signal or impulse is called an action potential. The action potential travels through a type of nerve cell that is called a motor neuron.

Option ‘A’ is correct

Note:
Thigh or back muscles are the best example of large motor units. Here a single neuron supplies thousands of muscle fibers in a muscle, as its axon splits into thousands of branches.