Neuron Structure and Function

Questions and Answers

What is the purpose of the six precordial, unipolar chest leads?

To record ECGs in the transverse plane (correct)

To measure electrical signals from the brain

To obtain ECGs in the frontal plane

To measure atrial repolarization

What is the aVR lead connected to?

LL and the center of two resistors connected to LA and RA

LA and LL

RA and the center of two resistors connected to LL and LA (correct)

RA and LL

What event produces the QRS complex?

Ventricular depolarization (correct)

Atrial depolarization

Ventricular repolarization

Atrial repolarization

What type of signals are obtained when measuring electrical activity from the brain?

Weak complex electrical signals Signup and view all the answers

What is the name of the recording of the signals from the brain?

Electroencephalogram Signup and view all the answers

What is the purpose of the reference electrode in EEG?

To provide a reference point for the signals Signup and view all the answers

What type of electrodes are often used for recording EEG signals?

Small discs of chlorided silver Signup and view all the answers

What is the location of the reference electrode in EEG?

On the ear (A1 or A2) Signup and view all the answers

What is the insulating layer that covers the axons of myelinated nerves?

Myelin Signup and view all the answers

Which type of nerve fiber conducts action potentials faster?

Myelinated nerves Signup and view all the answers

What is the approximate spacing between the nodes of Ranvier in a myelinated nerve fiber?

280a Signup and view all the answers

Which of the following factors affects the propagation speed of an action potential?

Both a and b Signup and view all the answers

How does the diameter of an axon affect the propagation speed of an action potential?

Larger diameter increases speed Signup and view all the answers

What is the approximate conduction speed (in m/s) of an unmyelinated nerve fiber with a radius of 0.2 μm?

3.6 Signup and view all the answers

What is the electromyogram (EMG)?

A record of the potentials from muscles during movement Signup and view all the answers

What is the relationship between capacitance and propagation speed of an action potential?

Inversely proportional Signup and view all the answers

What frequency range is associated with alpha waves?

8 to 13 Hz Signup and view all the answers

What physiological activity can interfere with EEG signal processing?

Muscle activity Signup and view all the answers

What is the function of electrodes in an electroretinogram (ERG)?

To record changes in potential from the retina Signup and view all the answers

Which wave is clinically significant due to its absence in retinal inflammation?

B wave Signup and view all the answers

What type of signal is recorded by an electrooculogram (EOG)?

Potential changes due to eye movement Signup and view all the answers

What does a higher frequency EEG signal indicate about a person's mental state?

The person is alert and focused Signup and view all the answers

Which of the following is not a type of brain wave recorded in EEG?

Gallop waves Signup and view all the answers

What initiates the electrical signal that controls the rhythmical action of the heart?

Sinoatrial node Signup and view all the answers

What is typically caused by external electrical signals in EEG processing?

Artifacts in the recordings Signup and view all the answers

How many times does the sinoatrial node typically fire in a minute?

Which part of the heart does the electrical signal travel to after the atria contract?

Atrioventricular node Signup and view all the answers

What do the electrodes used for an electrocardiogram primarily measure?

Electrical potentials generated by the heart Signup and view all the answers

Where are the standard limb leads primarily located for obtaining an ECG?

Left arm, right arm, and left leg Signup and view all the answers

What is the measurement of the potential between the right arm and left arm called?

Lead I Signup and view all the answers

What happens to the atria after they contract and pump blood into the ventricles?

They undergo repolarization Signup and view all the answers

What is the main function of the electrocardiogram (ECG)?

To record heart electrical activity Signup and view all the answers

What is the typical voltage difference between the inside and outside of a neuron at rest?

-60 to -90 mV Signup and view all the answers

What happens to the membrane of an axon when it is stimulated?

It becomes permeable to both Na+ and K+ ions. Signup and view all the answers

What is the term for the process of restoring the resting potential after an action potential?

Repolarization Signup and view all the answers

What is the function of the myelin sheath?

To insulate the axon and speed up the transmission of nerve impulses. Signup and view all the answers

What is the term for the regions of the axon that are not covered by the myelin sheath?

Nodes of Ranvier Signup and view all the answers

What is the role of the action potential in nerve signal transmission?

It allows for communication between neurons. Signup and view all the answers

What is the typical voltage inside an axon during depolarization?

+50 mV Signup and view all the answers

What is the main factor that contributes to the resting potential of a neuron?

The presence of more negative ions inside the cell than outside. Signup and view all the answers

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.