Pyridoxine is the chemical name of: MCQ with Answer and Explanation

Explanation:
The sinoatrial (SA) node is a specialized cluster of cells in the right atrium near the opening of the superior vena cava. It generates electrical impulses spontaneously, setting the pace of the heartbeat, hence called the pacemaker. The impulse spreads to the atrioventricular (AV) node, then to bundle of His and Purkinje fibers. Normal SA node firing rate is 60-100/min.

Explanation:
Motor (efferent) and sensory (afferent) neurons are correctly described. Interneurons are found in the CNS, not PNS. So 3 is incorrect.

Explanation:
Antonie van Leeuwenhoek was the first to observe and describe living microorganisms, including bacteria, using his single-lens microscopes. Robert Koch formulated Koch's postulates, a set of criteria to establish that a specific microorganism causes a specific disease. Alexander Fleming discovered penicillin; streptomycin was discovered by Selman Waksman. Thus, statements 1 and 2 are correct.