Electricity in the Nervous System

Electricity plays an important role in medicine.

What are the two aspects of electricity and magnetism in medicine?

What serves as the control and operation of nerves, muscles, and organs?

What is the fundamental unit of the nervous system?

What are the two parts that the nervous system can be divided into?

What does the central nervous system consist of?

What are the two types of nerve fibers in the peripheral nervous system?

The control of the autonomic nervous system is voluntary.

What are the functions of a neuron?

Which part of the neuron receives electrical messages from other neurons?

The soma of a neuron contains the nucleus.

Dendrites are specialized extensions of the cell body that carry information to the cell body from other cells.

What is the function of the axon?

Axons are typically 1 meter long.

Where are the signals from a neuron transmitted?

What is the basic unit of communication in the brain?

A chemical neurotransmitter is released from one cell and binds to receptors on the second cell.

What is the name of the potential difference created between the two environments of a cell?

The bio-potential can be measured using electrodes.

What are the two types of bio potential?

The inside of a cell is typically 60 to 90 mV more positive than the outside.

What is the term used to describe the large momentary change in resting potential that occurs when a neuron is stimulated?

The action potential propagates along the axon.

The action potential is the major method of transmission of signals within the body.

What is the record of the potentials from muscles during movement called?

A muscle is made up of many motor units.

What does a motor unit consist of?

Muscle action is initiated by an action potential that travels along an axon and is transmitted across the motor end plates into the muscle fibers.

It is easy to isolate a single muscle fiber during an EMG examination.

What are the two methods of measuring electrical signals during an EMG examination?

Action potential appears in EMG after a latency period.

EMGs of symmetrical muscles are compared to each other, or to those of normal individuals, to determine the action potential and latency periods.

Nerve damage may result in a decrease in the velocity of the action potential.

What is the recording of signals from the brain called?

EEG signals are primarily due to the electrical activity of the neurons in the cortex of the brain.

Electrodes for recording EEG signals are attached to the head at locations that are independent of what part of the brain is to be studied.

The reference electrode in an EEG recording is usually attached to the ear (A1 or A2).

Asymmetrical brain activity between the left and right sides is often a sign of brain disease.

The amplitude of EEG signals is high (about 50 μV)

Interference from external electrical signals often causes serious problems in EEG signal processing.

The frequencies of the EEG signals seem to be dependent upon the physical activity of the subject.

As a person becomes drowsy, the frequencies from 8 to 12 Hz (alpha wave) dominate the EEG.

The amplitude of the alpha wave decreases as a person moves from light sleep to deeper sleep.

Paradoxical sleep is characterized by rapid eye movement (REM) and is associated with dreaming.

What is the sensorimotor rhythm (SMR)?

The SMR appears in recordings of EEG, MEG, and ECG over the sensorimotor cortex.

Evoked responses are signals that result when the brain receives external stimuli.

EEGs typically show responses to all pulses of a stimulus.

What is the recording of potential changes produced by the eye when the retina is exposed to a flash of light called?

The ERG is more complicated than a nerve axon signal because it is the sum of many effects taking place within the eye.

The B wave of the ERG is the most interesting clinically, arising in the retina.

The B wave is absent in the ERG of patients with inflammation of the retina.

What is the recording of potential changes due to eye movements called?

A pair of electrodes is attached near the eye to measure the EOG.

The EOG provides information on the orientation of the eye and its angular velocity.

The heart's electrical system controls all the events that occur when the heart pumps blood.

What is the heart's electrical system also known as?

What is the heart test called that is a graphical picture of the heart's electrical activity?

What are the three main parts of the heart's electrical system?

The SA node is located in the left atrium.

The AV node is located on the interatrial septum close to the tricuspid valve.

The His-Purkinje system is located along the walls of the heart's atria.

A heartbeat is a complex cycle of electrical conductive events.

Each heartbeat has two basic parts: diastole and systole.

During diastole, the heart's atria and ventricles contract.

At the end of diastole, the heart's atria contract and pump blood into the ventricles.

The ventricles contract first, followed by the atria, during each heartbeat.

Ventricular systole involves the contraction of the ventricles, pumping blood out of the heart.

The SA node and the rest of the conduction system are at rest during the heartbeat.

The SA node initiates the action potential, which causes depolarization of nerves and muscles in both atria.

The SA node is also known as the pacemaker of the heart.

The delay of approximately 100 ms after the electrical signal reaches the AV node allows the atria to complete pumping blood before the impulse is transmitted to the atrioventricular bundle.

The impulse travels through the atrioventricular bundle, bundle branches, and Purkinje fibers, reaching the contractile fibers of the ventricle.

Ventricular contraction forces blood into the two systems, then ventricles are repolarized, completing the heartbeat cycle.

The normal heart rate at rest ranges between 60 and 100 beats per minute on average.

The SA node is responsible for adjusting the heart rate to meet the body's needs.

During periods of exercise, the heart rate decreases to conserve energy for physical exertion.

During periods of rest or sleep, the heart rate increases to meet the reduced oxygen demands of the body.

Changes in heart rate are a normal part of the heart's effort to meet the needs of the body.

In a normal ECG waveform, the P wave represents ventricular depolarization

The QRS complex represents ventricular depolarization.

The T wave represents atrial repolarization.

The P-R interval is measured from the start of the P wave to the start of the QRS complex.

The Q-T interval is measured from the start of the QRS complex to the end of the T wave.

The S-T segment is measured from the end of the QRS complex to the start of the T wave and represents the period when all cells are normally depolarized during that phase.

The P-R interval is typically between 0.12-0.2 seconds (3-5 small squares) on a standard ECG paper.

The QRS complex duration is typically less than or equal to 0.1 seconds (2.5 small squares) on a standard ECG paper.

The Q-T interval corrected for heart rate (QTc) is typically less than or equal to 0.44 seconds.

The location of the electrodes used for ECG recording does not significantly affect the measurements obtained.

The most common electrode placement for ECG recording is in the left arm (LA), right arm (RA), and left leg (LL).

A standard ECG graphing typically includes 6 sections, all of which are in the frontal plane.

The potential difference between any two electrodes provides information about the relative amplitude and direction of the electric dipole vector in the frontal plane.

What does lead I measure in an ECG?

The aVR augmented lead measures the potential difference between the right arm and the center of the resistance between the left leg and left arm.

The aVL augmented lead measures the potential difference between the left arm and the center of the resistance between the left leg and right arm.

The aVF augmented lead measures the potential difference between the left leg and the center of the resistance between the right arm and left arm.

The chest electrodes are typically placed in the 4th intercostal space.

V1 is placed in the 4th intercostal space, right of the sternum.

V3 is placed between V1 and V3.

V4 is placed in the fifth intercostal space in the nipple line.

V6 is placed in the mid axillary line on the same height as V4, but not necessarily in the 5th intercostal space.

The ECG can be used to diagnose problems with the heart, including arrhythmias.

Arrhythmias are an irregular pumping pattern which is quite common in young people and often exacerbated by exercise.

An ECG can reveal blockages in the blood supply to the heart, which can lead to myocardial infarction (heart attack).

Fibrillation is a condition where there is no coordinated pumping activity, which can lead to death if left untreated.