The impulse travels from the AV node into the bundle of His, which then splits into the right and left bundle branches. Those bundle branches receive the impulse from the bundle of His and carry it down the interventricular septum to the Purkinje fibers, which distribute the signal to the ventricular muscle for coordinated contraction. Terms like artifact, baseline, and amplifier relate to ECG measurement or equipment, not to cardiac conduction pathways, so they don’t describe structures that carry the impulse.

This question tests your understanding of terms used for lung tissue that has collapsed. Atelectasis is the medical term for the collapse of all or part of a lung, or of the tiny air sacs (alveoli), which leads to reduced or absent air exchange in that area. It can occur when an airway is blocked or when external pressure causes the lung to deflate. That makes it the best description for a collapsed lung. Bronchitis refers to inflammation of the bronchial tubes, causing coughing and mucus. Asthma is characterized by reversible narrowing of the airways with wheezing. COPD describes a chronic, progressive limitation of airflow. None of these describe a collapse of lung tissue the way atelectasis does.

The muscular system is made up of three muscle tissue types—skeletal, smooth, and cardiac—all working together to create movement, support, and regulate bodily functions. Skeletal muscle attaches to bones and enables voluntary movements; smooth muscle lines hollow organs and blood vessels to control involuntary actions; cardiac muscle forms the heart and drives circulation. The option that lists all three muscle types is identifying the muscular system, which is why it’s the best choice. The other options point to different systems or structures: nerves relate to the nervous system, blood vessels to the circulatory system, and ligaments to connective tissue.

The idea here is verifying that a sterilization cycle actually achieves the required level of microbial kill by using biological indicators. Spore testing uses non-pathogenic spores placed on paper strips to challenge the sterilizer; if the spores are killed, it indicates the cycle reached the necessary lethality for that load. After exposure, the strips are incubated to see if the spores germinate—growth means the process didn’t achieve sterilization for that run, while no growth confirms effective sterilization. Different spores are chosen based on the sterilization method (for steam, Bacillus stearothermophilus is common; for ethylene oxide, Bacillus atrophaeus). This approach goes beyond what chemical indicators or visual checks can do, because it directly tests whether the sterilization process can destroy hardy spores, not just whether the equipment reached a certain temperature or the packaging looks correct.