30 Questions
Which ion is primarily responsible for determining the resting membrane potential (RMP)?
K+
What is the approximate numerical value of the resting membrane potential (RMP)?
-70 mV
Why is the inside of the cell membrane negative at rest?
K+ is slowly leaking out of the cell
What is the approximate duration of a neural action potential?
2-4 ms
What is the approximate range of the resting membrane potential (RMP)?
-85 mV to -55 mV
During which phase of the action potential does hyperpolarization occur?
Afterhyperpolarization (AHP)
What is the approximate range of the threshold potential for an action potential?
0 mV to +40 mV
Which of the following can be diagnosed using conduction velocity tests?
All of the above
What is the conduction velocity for an alpha motor neuron?
100 meters/second
What is the conduction velocity for C fibers responsible for pain?
1 meter/second
What are the structural differences between alpha motor neurons and C fibers that contribute to the difference in their conduction velocity?
Alpha motor neurons are large and myelinated, while C fibers are small and unmyelinated.
What are the Nodes of Ranvier and their purpose?
Thin, unmyelinated strips of membrane along the length of a myelinated axon that increase conduction velocity.
How are electrical synapses molecularly coupled?
Via gap junctions
How do neurons encode the intensity of a signal?
By changing the frequency of action potentials
Which of the following statements about electrotonic conduction is true?
Electrotonic conduction is faster in myelinated neurons
What happens to the conduction of voltage when the membrane is depolarized?
The conduction of voltage increases
What is the role of myelin in electrotonic conduction?
Myelin decreases resistance and increases conduction
What is the effect of cytoplasm on electrotonic conduction?
Cytoplasm decreases resistance and increases conduction
What is the relationship between the diameter of a neuron and the speed of electrotonic conduction?
Larger diameter neurons have faster conduction
What is the basis of saltatory conduction?
Saltatory conduction is based on the myelination of neurons
What is the role of myelin in shielding the electric field?
Myelin shields and confines the electric field
What is the relationship between resistance and electrotonic conduction?
Increased resistance leads to slower conduction
Which type of potentials are based on electrotonic conduction?
Graded potentials
Which of the following is true about the threshold for an action potential?
The threshold is the voltage above which the cell is committed to completing an action potential.
What causes repolarisation during an action potential?
Inward Na+ channels inactivate.
What is a graded potential?
A change in the membrane potential that can vary in voltage amplitude and in time duration.
What is a refractory period?
A time duration after one action potential has just fired when another action potential either cannot be restimulated (absolute refractory period) OR is resistant to restimulation (relative refractory period) to begin a new action potential.
What is an equilibrium potential?
The voltage where the amount of a particular ion flowing out of the cell equals the amount of that ion flowing in.
What are the equilibrium potentials for Na+, K+, Ca2+, and Cl- in a typical cell?
ENa = ~ +55 mV, EK = ~ -90 mV, ECa = ~ +123 mV, ECl = ~ -40 mV
What would happen to the resting membrane potential if extracellular K+ suddenly increased?
The resting membrane potential would become less negative.
Study Notes
Action Potential Tutorial with Dr. Harry Witchel
- Resting membrane potential (RMP) is -70 mV and is maintained because of the slow leakage of K+ ions out of the cell, leaving negative anions behind.
- Neural action potential graph should last 2-4 ms, with RMP between -85 mV and -55 mV, overshoot between 0 and +40 mV, and afterhyperpolarization slightly above -90 mV.
- Resting membrane potential is determined by K+ ions moving down their concentration gradient out of the cell, while depolarization is caused by Na+ ions rapidly entering the cell.
- Repolarization is due to Na+ channels inactivating and K+ ions leaving the cell through delayed rectifier channels.
- Graded potentials are changes in membrane potential that can vary in voltage and duration, and they can trigger action potentials if large enough.
- Refractory period is a time after an action potential when another action potential cannot be restimulated or is resistant to restimulation, usually caused by high permeability to K+ ions.
- Equilibrium potential is the voltage where the amount of a specific ion flowing out of the cell equals the amount flowing in, based on diffusion and electrical forces.
- Equilibrium potentials for Na+, K+, Ca2+, and Cl- are approximately +55 mV, -90 mV, +123 mV, and -40 mV (or -65 mV), respectively.
- If extracellular K+ increases, the RMP becomes less negative because the driving force for K+ ions to leave the cell is reduced.
- Lidocaine is an example of a local anesthetic that works by blocking sodium channels, raising the threshold for action potentials and reducing local excitability.
- Conduction velocity is measured to investigate motor weakness and can detect pathological changes like conduction block or slowing.
- Alpha motor neurons have a conduction velocity of 100 m/s, while C fibers responsible for pain have a conduction velocity of 1 m/s. The structural differences between them, such as diameter and myelination, contribute to the difference in conduction velocity.
Test your knowledge on nerve conduction velocity and its role in diagnosing various conditions such as peripheral neuropathy, carpal tunnel syndrome, and spinal disc herniation. Learn about the conduction velocities of different motor neurons and their significance in detecting demyelination and degeneration.
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