JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B. Tech IV Year BIOMEDICAL INSTRUMENTATION Previous Question Paper (February/March - 2022 - R18)

A living cell is the fundamental structural and functional unit of the body. It consists of a central nucleus, which contains genetic material (DNA) and acts as the control center, surrounded by the cytoplasm, a jelly-like substance containing various organelles. The entire cell is enclosed by a cell membrane (plasma membrane), a semi-permeable lipid bilayer that regulates the passage of ions and nutrients.

Key constituents include:

• Mitochondria: Known as the powerhouse of the cell, responsible for ATP production through cellular respiration.
• Endoplasmic Reticulum (ER): Involved in the synthesis of proteins (rough ER) and lipids (smooth ER).
• Golgi Apparatus: Responsible for modifying, sorting, and packaging proteins for secretion.
• Lysosomes: Contain digestive enzymes for breaking down waste materials.
• Ribosomes: Sites of protein synthesis.

Body surface recording electrodes are non-invasive sensors used to detect biopotentials generated by internal organs, such as the heart (ECG), brain (EEG), or muscles (EMG). These electrodes act as transducers, converting ionic currents in the body into electronic currents in the measurement circuit.

Common types include:

• Metal Plate Electrodes: The most common type, typically made of stainless steel or nickel silver. They are often used with conductive electrode paste or gel to reduce skin-electrode impedance.
• Suction Cup Electrodes: A variation of the metal plate electrode that uses a rubber bulb to create a vacuum, holding the electrode firmly against the skin surface. These are frequently used in clinical ECG monitoring.
• Floating Electrodes: Designed to minimize motion artifacts. The metal contact is recessed and does not touch the skin directly; instead, it is separated by an electrolyte gel, which acts as a buffer against mechanical movement.
• Disposable Electrodes: Usually made of silver/silver-chloride (Ag/AgCl) due to their excellent stability and low noise characteristics. These are pre-gelled and designed for single-use to prevent cross-contamination.

The performance of these electrodes depends heavily on the interface impedance, which is minimized by the use of electrolytic gels that hydrate the skin's outer layer (stratum corneum), thereby improving electrical contact.