Final answer:
The question discusses the stretch reflex in skeletal muscles initiated by sensory neurons in response to stretching, aiming to maintain muscle length and tone. It also touches on how the frequency of neuron action potentials can influence muscle tension and contraction, leading to graded muscle responses and summation effects.
Step-by-step explanation:
The question relates to the sensory neurons firing action potentials (AP's) in response to muscle stretching, which describes the stretch reflex in skeletal muscle. This reflex involves a muscle spindle receptor that gets activated when a muscle is stretched. The neuron attached to this receptor sends out an AP leading to the muscle's direct contraction. Additionally, the information sent also inhibits the motor neurons that supply the antagonist muscles, helping to maintain the muscle tone and length constant, which is necessary for posture and stability.
Moreover, muscle contraction is governed by several factors, including the frequency of AP's from motor neurons, which can lead to various levels of muscle tension. This is described as a graded muscle response. If AP's are frequent enough, they can result in summation, increasing muscle tension. This can lead to incomplete tetanus or even complete tetanus if the AP's are sustained without any relaxation phase.