Questions and Answers
What is the purpose of the six precordial, unipolar chest leads?
What is the aVR lead connected to?
What event produces the QRS complex?
What type of signals are obtained when measuring electrical activity from the brain?
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What is the name of the recording of the signals from the brain?
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What is the purpose of the reference electrode in EEG?
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What type of electrodes are often used for recording EEG signals?
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What is the location of the reference electrode in EEG?
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What is the insulating layer that covers the axons of myelinated nerves?
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Which type of nerve fiber conducts action potentials faster?
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What is the approximate spacing between the nodes of Ranvier in a myelinated nerve fiber?
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Which of the following factors affects the propagation speed of an action potential?
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How does the diameter of an axon affect the propagation speed of an action potential?
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What is the approximate conduction speed (in m/s) of an unmyelinated nerve fiber with a radius of 0.2 μm?
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What is the electromyogram (EMG)?
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What is the relationship between capacitance and propagation speed of an action potential?
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What frequency range is associated with alpha waves?
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What physiological activity can interfere with EEG signal processing?
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What is the function of electrodes in an electroretinogram (ERG)?
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Which wave is clinically significant due to its absence in retinal inflammation?
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What type of signal is recorded by an electrooculogram (EOG)?
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What does a higher frequency EEG signal indicate about a person's mental state?
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Which of the following is not a type of brain wave recorded in EEG?
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What initiates the electrical signal that controls the rhythmical action of the heart?
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What is typically caused by external electrical signals in EEG processing?
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How many times does the sinoatrial node typically fire in a minute?
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Which part of the heart does the electrical signal travel to after the atria contract?
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What do the electrodes used for an electrocardiogram primarily measure?
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Where are the standard limb leads primarily located for obtaining an ECG?
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What is the measurement of the potential between the right arm and left arm called?
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What happens to the atria after they contract and pump blood into the ventricles?
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What is the main function of the electrocardiogram (ECG)?
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What is the typical voltage difference between the inside and outside of a neuron at rest?
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What happens to the membrane of an axon when it is stimulated?
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What is the term for the process of restoring the resting potential after an action potential?
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What is the function of the myelin sheath?
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What is the term for the regions of the axon that are not covered by the myelin sheath?
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What is the role of the action potential in nerve signal transmission?
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What is the typical voltage inside an axon during depolarization?
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What is the main factor that contributes to the resting potential of a neuron?
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Study Notes
Electrical Potentials of Nerves
- Neurons are usually insulated by a myelin sheath, except at Nodes of Synapse where signal transparency allows one-directional flow.
- The resting potential of a neuron is a voltage difference across the membrane, ranging from -60 to -90 mV, indicating polarization with more negative ions inside.
Action Potential
- When a neuron is stimulated, resting potential changes, and action potential propagates along the axon.
- Depolarization occurs due to Na+ ions entering the neuron, causing the inside to briefly reach +50 mV.
- Repolarization follows as K+ ions exit, restoring the resting potential.
Types of Nerve Fibers
-
Myelinated Nerves:
- Covered with myelin sheath and Nodes of Ranvier are present.
- Conduct action potentials faster due to low electrical capacitance.
- Conduction speed formula: u ≈ 12(a + b), where (a) is the axon's radius and (b) is myelin thickness.
-
Unmyelinated Nerves:
- Make up about 2/3 of axon fibers in the body.
- Radii range from 0.05 to 0.6 μm; speed of conduction is slower, approximated by u ≈ 1.8 √a.
Factors Affecting Action Potential Propagation Speed
- Speed is influenced by resistance within the axon core and capacitance across the membrane.
- Larger axon diameters decrease internal resistance, increasing velocity.
- Greater stored charge (capacitance) slows down depolarization and action potential speed.
Electrical Signals from Muscles
- Electromyogram (EMG) records electrical activity in muscles during movement for diagnostic purposes.
Electrical Signals from the Heart
- The sinoatrial (SA) node acts as the heart's pacemaker, firing approximately 72 times per minute to initiate the cardiac cycle.
- Depolarization spreads from the SA node to the atria, followed by repolarization.
- Atrioventricular (AV) node further propagates the electrical signal to the ventricles.
Electrocardiogram (ECG)
- ECG measures heart potentials through surface electrodes, typically placed on the left arm, right arm, and left leg.
- Standard limb leads include Lead I (RA to LA), Lead II (RA to LL), and Lead III (LA to LL).
- Augmented leads (aVR, aVL, aVF) measure potential in different configurations.
- Six additional precordial leads (V1-V6) are positioned across the chest wall for comprehensive cardiac monitoring.
Heart Cycle Electrical Events
- P wave: Atrial depolarization.
- QRS complex: Ventricular depolarization.
- T wave: Ventricular repolarization.
Electrical Signals from the Brain
- Electroencephalogram (EEG) records weak electrical activity from the brain's cortex.
- Electrodes are typically attached to the scalp, with a reference electrode placed on the ear.
- EEG frequency bands include alpha (8-13 Hz), beta (above 13 Hz), delta (0.5-3.5 Hz), and theta (4-7 Hz), correlating with mental states.
Electrical Signals from the Eye
- Electroretinogram (ERG) measures electrical potential changes in response to light, using electrodes placed on the cornea and another on the ear or forehead.
- B wave is significant clinically; its absence indicates retinal inflammation.
- Electrooculogram (EOG) records eye movement potential changes, providing insight into eye orientation and motion dynamics.
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Description
Quiz about the structure and function of neurons, including the myelin sheath, nodes of synapse, and electrical potentials.