Biomedical Instrumentation Questions and Answers – Origin of Bioelectric Signals

Answer.1. Cellular

Explanation:-

Bioelectric potentials are generated at a cellular level. Bioelectric potentials are produced as a result of the electrochemical activity of a certain class of cells, known as excitable cells, that are components of nervous, muscular, or glandular tissue. Electrically they exhibit a resting potential and, when appropriately stimulated, an action potential.

Answer.3. Electrochemical

Explanation:-

The electrochemical activity in certain types of body cells gives rise to ionic voltages usually termed as bioelectric potentials. Electrically they exhibit a resting potential and, when appropriately stimulated, an action potential.

Generally, such cells in the resting state have a lower base value of ionic potential, the resting potential. Further, on account of some applied stimulus, the cells become excited and the ionic potential rises to a certain higher value. The magnitude of the bioelectric potential in the excited state is designated as the action potential. Now, a cell that has been excited and displays action potential is said to be depolarised. In other words, the process of changing the resting potential state to the action potential state due to an applied stimulus is termed

Answer.2. Ionic

Explanation:-

Bioelectric potentials are generated at a cellular level and the source of these potentials is ionic in nature. A cell consists of an ionic conductor separated from the outside environment by a semipermeable membrane which acts as a selective ionic filter to the ions. This means that some ions can pass through the membrane freely whereas others cannot do so.

Surrounding the cells of the body are body fluids, which are ionic and which provide a conducting medium for electric potentials. The principal ions involved with the phenomena of producing cell potentials are sodium (Na⁺), potassium (K⁺) and chloride (Cl^–). The membrane of excitable cells readily permits the entry of K⁺ and Cl^–  but impedes the flow of Na⁺ even though there may be a very high concentration gradient of sodium across the cell membrane.

Answer.4. All of the above

Explanation

The principal ions involved with the phenomena of producing cell potentials are sodium (Na⁺), potassium (K⁺) and chloride (Cl^–). The membrane of excitable cells readily permits the entry of K⁺ and Cl^–  but impedes the flow of Na⁺ even though there may be a very high concentration gradient of sodium across the cell membrane.

Answer.3. Both 1 & 2

Explanation:-

The origins of these biopotentials can be traced to the electric activity at the cellular level. The electric potential across a cell membrane is the result of different ionic concentrations that exist inside and outside the cell. The type of potential generated electrically in a cell as a result of the electrochemical activity is

1. Resting Potential
2. Action Potential

Resting potential:- Electrically charged molecules called ions are found inside each neuron. Other ions lie outside the neuron. Some ions have a positive electrical charge, whereas others have a negative charge. When a neuron is inactive (or resting), more of these “plus” charges exist outside the neuron and more “minus” charges exist inside. This charge allows each neuron to act like a tiny biological battery. The electrical charge of an inactive neuron is called its resting potential.

Action Potential:- When a cell receives a stimulus above a certain “threshold” value, this balance is upset, and the cell will go through a cycle known as an “action potential”. It is by this method that impulses, technically called electrochemical impulses, are transmitted from cell to cell.

Answer.4. H⁺

Explanation:-

The principal ions involved with the phenomena of producing cell potentials are sodium (Na⁺), potassium (K⁺) and chloride (Cl^–). The membrane of excitable cells readily permits the entry of K⁺ and Cl^–  but impedes the flow of Na⁺ even though there may be a very high concentration gradient of sodium across the cell membrane.

This results in the concentration of the sodium ion more on the outside of the cell membrane than on the inside. Since sodium is a positive ion, in its resting state, a cell has a negative charge along the inner surface of its membrane and a positive charge along the outer portion. The unequal charge distribution is a result of certain electrochemical reactions and processes occurring within the living cell and the potential measured is called the resting potential. The cell in such a condition is said to be polarized. A decrease in this resting membrane potential difference is called depolarization.

Answer.3. Resting Potential

Explanation:-

The relatively static membrane potential of quiescent cells is called the resting membrane potential (or resting voltage), as opposed to the specific dynamic electrochemical phenomena called an action potential and graded membrane potential.

The resting potential has a voltage of 70 mV. It is said to be “resting” because it pertains to the condition when the cell is not disturbed or stimulated. The resting potential is the static membrane potential of quiescent cells.

Answer.2. Action Potential

Explanation:-

The action potential is the localized, momentary change in the membrane potential of a cell. It occurs upon stimulation of the cell. Its occurrence leads to the transmission of an electrical impulse. In the span of a few milliseconds, the membrane potential ascends from the resting potential value. This voltage is about -70 mV. From this negative value, the membrane potential rises to a positive value, around +40 mV.

or

When a cell receives a stimulus above a certain “threshold” value, this balance is upset, and the cell will go through a cycle known as an “action potential”. It is by this method that impulses, technically called electrochemical impulses, are transmitted from cell to cell.

Sequence of event in Action Potential

Initially, in its resting state, a cell has a negative charge along the inner surface of its membrane and a lesser negative charge along the outer portion. The cell, in such a condition, is said to be polarized and in effect acts as a tiny biological battery.

When excited or stimulated, the membrane permeability to sodium (Na+) ions is increased, resulting in sodium ions flowing into the cell, thereby, the outer side of the cell membrane becomes momentarily negative with respect to the interior). The voltage inside the cell rises (becomes less negative). This process is called depolarization and the cell potential changes to approximately +40 mV. At this stage, when the electrical balance is achieved again, the cell is referred to as being in a depolarized state.

Answer.2. Refractory period

Explanation

Refractory Period after excitation

Since the energy associated with the action potential is developed from metabolic processes within the cell itself and not from the stimulus, a finite period of time, known as the refractory finite period of time, known as the refractory period, is required for metabolic processes within the cell to return the cell to its pre-stimulus state. This refractory period has been observed in most cells found in the nervous system. This refractory period has two parts: The first in which no stimulus, however strong, will cause depolarization (the absolute refractory period), and the second when depolarization occurs only if the stimulus is of more than normal threshold strength (the relative refractory period).

Answer.2. External Action potential

Explanation

The potential may be recorded with a microelectrode; however, in most bioelectric measurements, this potential is recorded by electrodes external to the actual cell.

External Electrodes

These external electrodes typically would record the net action of many hundreds of cells. When recording with external electrodes, an action potential is produced between these electrodes during periods of current flow; that is to say, no potential exists when cells are either in their depolarized or repolarized state. A potential exists only while the cell is changing from one state to another. As the external action potential is generated by the external current that flows during cell activity, the shape of the action potential is related to the variation of this current with time.

External Action Potential

The external potential field rises to its maximum value sometime during the regenerative breakdown phase of the membrane. The external action potential that is recorded from the cell is somewhat similar to a mathematical time derivative of the trans-membrane potential. This potential is detected with maximum amplitude when one electrode is placed as near as possible to the active area and the other electrode is located in a completely inactive or remote area. It is detected with reduced amplitude as the electrodes are placed closer to each other so they intercept smaller elements of potential difference.