p.26
Action potential basics
Can summation occur in action potentials?
No, summation is not possible in action potentials.
p.3
Ion channels and their permeability
What effect does increasing Na+ permeability have on membrane potential (Vm)?
Increasing Na+ permeability makes the membrane potential (Vm) more positive, moving it closer to the equilibrium potential for sodium (E_Na).
p.15
Ion channels and their permeability
What does the selectivity filter in voltage gated Na+ channels consist of?
Negatively charged amino acids such as glutamate.
p.19
Action potential basics
What initiates the propagation of an action potential?
Opening of Na+ channels generates local current that depolarizes adjacent membrane, opening more Na+ channels.
p.8
Effect of low plasma calcium on threshold potential
How do calcium ions affect Na channels?
Calcium ions bind to the exterior surfaces of the voltage-gated sodium channel.
p.19
Action potential basics
What is the 'Propagation' phase in the context of action potential?
It is the spread of current along the membrane, leading to the opening of more Na+ channels and further depolarization.
p.12
Action potential basics
How is information encoded in action potentials?
The frequency of action potentials encodes information, while the amplitude of action potentials remains constant.
p.8
Effect of low plasma calcium on threshold potential
What happens to the voltage level required to open the sodium gate when plasma calcium is low?
The voltage level (threshold) required to open the sodium gate is reduced, making the threshold potential more negative and closer to Vm.
p.6
Ion channels and their permeability
What happens to the inactivation gate of voltage-gated sodium channels after the channel opens?
The inactivation gate closes shortly after the channel opens, stopping the flow of sodium ions.
p.5
Effect of high and low plasma potassium on threshold potential
How does the threshold potential change when serum K+ increases from 4 mEq/L to 6 mEq/L?
The threshold potential decreases from 15 mV to 11 mV.
p.18
Ion channels and their permeability
What happens to Na channels during the absolute refractory period?
Na channels are voltage inactivated.
p.21
Action potential basics
How does myelination affect the conduction of action potentials?
Myelination allows action potentials to jump between nodes of Ranvier, increasing conduction speed.
p.26
Action potential basics
How does the strength of the stimulus affect an electrotonic potential?
An electrotonic potential is proportional to stimulus strength (graded).
p.26
Action potential basics
How is an action potential propagated?
An action potential is propagated unchanged in magnitude.
p.22
Action potential basics
What type of disease is Multiple Sclerosis (MS)?
MS is an immune-mediated inflammatory demyelinating disease of the CNS.
p.31
Action potential basics
What happens to the membrane potential during Phase 3 of the sinoatrial node action potential?
It repolarizes due to the outward K+ current.
p.22
Action potential basics
What is the female-to-male ratio for Multiple Sclerosis incidence?
The female-to-male ratio is 2:1.
p.26
Action potential basics
Can summation occur in electrotonic potentials?
Yes, electrotonic potentials exhibit summation.
p.16
Ion channels and their permeability
What does the ratio of conductances graph represent?
The ratio of Na+ conductance to K+ conductance during an action potential.
p.19
Action potential basics
What is the result of local depolarization in the propagation of an action potential?
It generates a local current that depolarizes adjacent membrane, opening more Na+ channels.
p.12
Action potential basics
Why do local anesthetics usually produce analgesia without paralysis?
Local anesthetics are more effective against small diameter neurons with a large surface area to volume ratio, such as small C-fibers that conduct pain sensations, rather than large alpha-motorneurons.
p.5
Effect of high and low plasma potassium on membrane potential
Why does an increase in extracellular potassium concentration make the cell more excitable?
Because the resting membrane potential is closer to the threshold potential.
p.21
Action potential basics
Why do nonmyelinated axons conduct action potentials more slowly?
In nonmyelinated axons, action potentials must propagate continuously along the entire length of the axon.
p.20
Action potential basics
What is one benefit of saltatory conduction in terms of speed?
It increases the velocity of action potential propagation.
p.8
Effect of low plasma calcium on threshold potential
Why can tetany in respiratory muscles be lethal?
Because it can impair breathing.
p.3
Ion channels and their permeability
What effect does increasing K+ permeability have on membrane potential (Vm)?
Increasing K+ permeability makes the membrane potential (Vm) more negative, moving it closer to the equilibrium potential for potassium (E_K).
p.15
Ion channels and their permeability
What type of channels have a selectivity filter?
Voltage Gated Na+ Channels.
p.1
Resting membrane potential for different cell types
Why is the resting membrane potential for RBCs so close to 0 mV?
Resting membrane permeability to sodium ions is high compared to most other cells.
p.7
Effect of low plasma calcium on threshold potential
What is the effect of low plasma calcium on threshold potential?
Threshold potential becomes more negative, and thus closer to Vm. This increases the excitability of the cell.
p.20
Ion channels and their permeability
Why do action potentials only occur at the nodes during saltatory conduction?
Because Na+ channels are concentrated at the nodes.
p.23
Transmission at a Chemical Synapse
What are the two types of synapses?
Excitatory and Inhibitory
p.19
Action potential basics
What occurs during the 'Stimulated' phase of action potential propagation?
Local depolarization occurs due to the opening of Na+ channels.
p.6
Ion channels and their permeability
What is the significance of the positive charges on the voltage sensor in voltage-gated sodium channels?
The positive charges on the voltage sensor, which could be arginine, respond to changes in membrane potential, facilitating the opening of the channel.
p.12
Action potential basics
What type of fibers carry information of lesser importance and conduct pain sensations?
Slowly conducting unmyelinated fibers, such as nonmyelinated C-fibers, carry information of lesser importance and conduct pain sensations.
p.18
Action potential basics
What is the relative refractory period?
A period during which a greater than normal stimulus is required to elicit an action potential (AP).
p.31
Action potential basics
What characterizes Phase 4 of the sinoatrial node action potential?
Slow depolarization due to inward Na+ current.
p.22
Action potential basics
What is the prevalence of Multiple Sclerosis in the US?
About 1 person per 1000 in the US is thought to have the disease.
p.20
Action potential basics
How does saltatory conduction contribute to energy conservation?
By reducing the amount of ion exchange needed along the axon, thus conserving energy.
p.33
Ion channels and their permeability
What effect does increasing the permeability to Na+ and Ca++ ions have on the SA node action potential?
It causes the sympathetic mechanism effect, which increases the rate of depolarization.
p.33
Ion channels and their permeability
How does the sympathetic mechanism affect the SA node action potential?
It increases the permeability to Na+ and Ca++ ions, leading to a faster depolarization.
p.19
Action potential basics
What happens to the membrane during the 'Rest' phase of action potential propagation?
The membrane is at its resting potential with no significant ion movement.
p.6
Action potential basics
Why do voltage-gated sodium channels open when the membrane potential becomes less negative and reaches threshold?
Voltage-gated sodium channels open because the voltage sensor detects the change in membrane potential, causing the gate to open.
p.12
Action potential basics
How do action potentials deliver sensory information to the CNS?
Action potentials (APs) in sensory nerves deliver sensory information to the CNS. Local anesthetics can block these APs, producing analgesia without paralysis.
p.12
Action potential basics
What cellular responses can action potentials initiate in non-nervous tissues?
In non-nervous tissues, action potentials can initiate muscle contraction and secretion, such as the release of epinephrine from chromaffin cells of the medulla.
p.18
Action potential basics
How do refractory periods affect the frequency of action potentials?
Refractory periods limit the maximum frequency of action potentials.
p.31
Action potential basics
What occurs during Phase 0 of the sinoatrial node action potential?
Depolarization due to inward Ca++ current.
p.8
Effect of low plasma calcium on threshold potential
How does low calcium levels in blood cause muscle tetany?
Low calcium increases excitability of nerve axons by causing sodium channels to open following very small increases in Vm.
p.2
Net driving force on K+ ions
How is the net driving force on any ion calculated?
It is the difference in millivolts between the membrane potential (Vm) and the equilibrium potential for that ion (Eion).
p.6
Ion channels and their permeability
What is the function of the selectivity filter in voltage-gated sodium channels?
The selectivity filter ensures that only sodium ions can pass through the channel.
p.5
Effect of high and low plasma potassium on membrane potential
What is the effect of an increase in extracellular potassium concentration on cell excitability?
An increase in extracellular potassium concentration increases the excitability of the cell because the resting membrane potential is closer to the threshold potential.
p.21
Action potential basics
What is the difference in conduction velocity between nonmyelinated and myelinated axons?
Myelinated axons have a faster conduction velocity compared to nonmyelinated axons.
p.21
Action potential basics
What structural feature of myelinated axons contributes to their increased conduction velocity?
The presence of myelin sheaths and nodes of Ranvier.
p.31
Action potential basics
What is the significance of the inward Ca++ current in the sinoatrial node action potential?
It causes depolarization during Phase 0.
p.22
Action potential basics
Which demographic has the highest incidence of Multiple Sclerosis?
Whites of northern European descent have the highest incidence.
p.17
Action potential basics
What does each peak in a compound action potential recording represent?
A set of axons with similar conduction velocity.
p.17
Action potential basics
What is seen as a small (mV) voltage signal on the body surface?
The passage of action potentials in all axons of nerves.
p.25
Action potential basics
What is the effect of 'local current flow' in a neuron?
It depolarizes adjacent regions of a neuron.
p.25
Action potential basics
How does the depolarization change with distance when stimulation is restricted to a small area of the membrane?
The depolarization will be greatest at the point of stimulation and will fall exponentially with distance.
p.28
Transmission at a Chemical Synapse
What is a ligand?
A ligand is any substance that binds to a receptor.
p.28
Transmission at a Chemical Synapse
How are receptors often named and classified?
Receptors are often named and classified largely by reference to the ligand.
p.28
Transmission at a Chemical Synapse
How are receptors often subdivided?
Receptors are often subdivided by reference to ligands.
p.32
Ion channels and their permeability
What effect does increasing the permeability to K+ ions have on the SA node action potential?
It causes the parasympathetic mechanism effect.
p.15
Ion channels and their permeability
What is the role of the selectivity filter in voltage gated Na+ channels?
To selectively allow Na+ ions to pass through the channel.
p.23
Transmission at a Chemical Synapse
What is an axo-dendritic synapse?
A synapse between the axon of one neuron and the dendrite of another neuron
p.6
Ion channels and their permeability
What role does the voltage sensor play in the operation of voltage-gated sodium channels?
The voltage sensor detects changes in membrane potential and triggers the opening of the gate.
p.12
Action potential basics
What factors affect the speed of action potential transmission over distance?
The speed of transmission depends on the fiber size and whether the fiber is myelinated. Larger and myelinated fibers conduct signals faster.
p.18
Action potential basics
What is the absolute refractory period?
A period during which an action potential (AP) is not possible due to voltage inactivation of Na channels.
p.18
Action potential basics
Why is a greater than normal stimulus required during the relative refractory period?
Because the membrane potential is still returning to its resting state, making it harder to reach the threshold for another action potential.
p.26
Action potential basics
How does the strength of the stimulus affect an action potential?
An action potential is independent of stimulus strength (all or none).
p.26
Action potential basics
How is an electrotonic potential propagated?
An electrotonic potential is not propagated but decremental with distance.
p.31
Action potential basics
What is the role of the inward Na+ current in the sinoatrial node action potential?
It contributes to the slow depolarization during Phase 4.
p.16
Ion channels and their permeability
What happens to the Na+ conductance during the initial phase of an action potential?
Na+ conductance increases rapidly.
p.16
Ion channels and their permeability
How does K+ conductance change during an action potential?
K+ conductance increases after the peak of the action potential and remains elevated during repolarization.
p.25
Action potential basics
How are local potentials graded?
A bigger stimulus results in a bigger response.
p.27
Transmission at a Chemical Synapse
How do neurotransmitters travel across the synaptic cleft?
They diffuse across the synaptic cleft, which is less than 20 nm wide.
p.9
Hyperkalemia and its effect on membrane potential
What is the initial treatment for hyperkalemia?
Intravenous administration of calcium.
p.22
Action potential basics
Why do patients with Multiple Sclerosis often have difficulty describing their symptoms?
Because the symptoms can resolve and reoccur, making them difficult to describe.
p.22
Action potential basics
What happens when the resolution of neurologic deficits in Multiple Sclerosis becomes incomplete or too frequent?
The diagnostic dilemma begins.
p.16
Ion channels and their permeability
At what point does the Na+ conductance peak during an action potential?
Na+ conductance peaks at the beginning of the action potential, around 0.5 milliseconds.
p.9
Hyperkalemia and its effect on membrane potential
How does high potassium (K+) affect the membrane potential (Vm)?
High K+ makes Vm less negative, moving it from −90 mV to −80 mV.
p.27
Transmission at a Chemical Synapse
What happens when Ca2+ enters the presynaptic neuron?
It causes the release of neurotransmitters from vesicles.
p.27
Transmission at a Chemical Synapse
What happens when neurotransmitters bind to receptors on the postsynaptic neuron?
It causes the opening of receptor-operated channels, leading to depolarization.
p.24
Ion channels and their permeability
What determines whether the postsynaptic membrane is hyperpolarized or depolarized?
The selectivity of the channels for particular ions.
p.28
Transmission at a Chemical Synapse
What are the two types of acetylcholine (ACh) receptors?
Nicotinic (nACh) and muscarinic (mACh) receptors.
p.14
Ion channels and their permeability
What is the state of the K+ channel during the repolarization phase?
The K+ channel is open during the repolarization phase (+35 to -90 mV).
p.11
Action potential basics
How is information coded in action potentials?
Information is coded by frequency, not amplitude.
p.29
Hyperkalemia and its effect on membrane potential
What effect do inhibitory synapses have on the postsynaptic cell?
They hyperpolarize the postsynaptic cell and depress excitability.
p.29
Ion channels and their permeability
What ions are excitatory synapses permeable to?
Cations (Na+, K+, and Ca2+).
p.29
Transmission at a Chemical Synapse
What is an excitatory postsynaptic potential (EPSP)?
A depolarization of the postsynaptic cell that enhances excitability.
p.13
Ion channels and their permeability
What do the terms 'gate' and 'gating' refer to in ion channels?
Transitions between different states of the channel protein.
p.4
Action potential basics
What is the threshold potential?
The threshold potential is the membrane potential at which an action potential is generated.
p.30
Action potential basics
What happens during Phase 2 of the ventricular action potential?
Inward Ca++/Na+ current and decreased outward K+ current (plateau).
p.10
Action potential basics
What is an action potential?
A regenerating depolarization of membrane potential that propagates along an excitable membrane.
p.22
Action potential basics
What are some common initial symptoms of Multiple Sclerosis?
Paresthesias of a hand that resolves, followed by weakness in a leg or visual disturbances.
p.17
Action potential basics
How is conduction velocity calculated?
By dividing the distance between R1 and R3 by the time taken to traverse that distance (distance/time = velocity).
p.25
Action potential basics
What is a key characteristic of local potentials regarding refractoriness?
Local potentials do not induce refractoriness.
p.17
Action potential basics
What happens to the waveform as recordings are made further from the site of stimulation?
The waveform develops into several discrete peaks.
p.9
Hyperkalemia and its effect on membrane potential
How close does the membrane potential (Vm) get to the threshold potential in hyperkalemia?
Vm is only 5 mV more negative than the threshold potential.
p.24
Transmission at a Chemical Synapse
In fast synapses, what do transmitter substances bind to on the postsynaptic cell?
Receptors to directly open ion channels (ligand-gated).
p.14
Ion channels and their permeability
What happens to Na+ conductance during the action potential?
Na+ conductance increases rapidly during the action potential.
p.24
Ion channels and their permeability
Towards what will the membrane potential move in the postsynaptic cell?
Towards the equilibrium potential for the permeant ion(s).
p.24
Action potential basics
What happens when synaptic responses reach the threshold?
They initiate an action potential.
p.11
Action potential basics
What is the typical threshold voltage for an action potential?
Usually 15 mV positive to resting potential.
p.11
Action potential basics
Do action potentials have constant amplitude?
Yes, action potentials have constant amplitude.
p.11
Action potential basics
What is the formula for the conduction velocity of myelinated fibers?
Myelinated fiber diameter (in mm) × 4.5 = velocity in m/s.
p.4
Action potential basics
What is excitability in the context of membrane potential?
Excitability refers to the ability of a cell to respond to a stimulus and generate an action potential.
p.30
Action potential basics
What characterizes Phase 1 of the ventricular action potential?
Outward K+ current (early repolarization).
p.10
Action potential basics
Do action potentials summate?
No, they have a constant amplitude and do not summate.
p.22
Action potential basics
Why do patients with Multiple Sclerosis frequently not bring their complaints to doctors?
Because the symptoms often resolve on their own.
p.16
Action potential basics
What occurs during the positive afterpotential phase?
The membrane potential remains slightly above the resting potential due to the delayed closing of K+ channels.
p.9
Hyperkalemia and its effect on membrane potential
Why is hyperkalemia considered one of the deadliest electrolyte disorders?
Because it can cause deadly cardiac arrhythmias.
p.27
Transmission at a Chemical Synapse
What triggers the opening of voltage-gated Ca2+ channels in the presynaptic neuron?
The arrival of an action potential (AP).
p.25
Action potential basics
What happens to the membrane potential during subthreshold stimuli?
The membrane potential does not reach the threshold voltage and slowly returns to the resting value.
p.25
Action potential basics
Why are these potentials called 'electrotonic' or 'local' potentials?
Because the effect is 'local' to the stimulus.
p.28
Transmission at a Chemical Synapse
Which substances are considered ligands?
Acetylcholine, Norepinephrine, Epinephrine, Serotonin (5-HT), Dopamine, Glycine, Glutamate, Adenosine.
p.28
Transmission at a Chemical Synapse
What are 'physiological' ligands?
Acetylcholine and norepinephrine are 'physiological' ligands, i.e., provided by the body.
p.24
Transmission at a Chemical Synapse
What can subthreshold synaptic responses do?
They can summate with others.
p.13
Ion channels and their permeability
What determines the permeability of the axon membrane to ions?
The number of open channels.
p.29
Transmission at a Chemical Synapse
What is an inhibitory postsynaptic potential (IPSP)?
A hyperpolarization of the postsynaptic cell that depresses excitability.
p.4
Action potential basics
What is depolarization?
Depolarization is the process of the membrane potential becoming more positive, moving towards 0 mV.
p.4
Effect of high and low plasma potassium on membrane potential
What is the effect of low plasma potassium on membrane potential?
Low plasma potassium (hypokalemia) increases the membrane potential, making it more negative.
p.10
Action potential basics
What does it mean for a membrane to be excitable?
It is capable of generating action potentials.
p.17
Action potential basics
What does the first signal to arrive at a distant recording site indicate?
It has traveled the fastest.
p.16
Ion channels and their permeability
What is the relationship between Na+ and K+ conductance during the repolarization phase?
During repolarization, Na+ conductance decreases while K+ conductance increases.
p.9
Effect of high and low plasma potassium on threshold potential
What is the threshold potential in the context of hyperkalemia?
The threshold potential is −75 mV.
p.9
Effect of low plasma calcium on threshold potential
What effect does increased plasma calcium concentration have on the threshold potential?
It makes the threshold potential less negative, changing it from −75 mV to −65 mV.
p.24
Ion channels and their permeability
What happens to the permeability of the postsynaptic membrane when transmitter substances bind to receptors?
The permeability to ions is increased.
p.27
Transmission at a Chemical Synapse
How long does it take for neurotransmitters to diffuse across the synaptic cleft?
Approximately 0.5 milliseconds.
p.14
Ion channels and their permeability
What is the state of the Na+ inactivation gate during the inactivated state?
The Na+ inactivation gate is closed during the inactivated state (+35 to -90 mV, delayed).
p.14
Action potential basics
What is the positive afterpotential?
The positive afterpotential is a phase where the membrane potential is more positive than the resting potential after an action potential.
p.11
Action potential basics
What determines the conduction velocity of action potentials in fibers?
The diameter of the fiber; larger diameter fibers conduct faster than smaller fibers.
p.13
Ion channels and their permeability
What ions do Ca channels pass and why are they important?
Only Ca ions; they are important in synaptic transmission.
p.4
Action potential basics
What is hyperpolarization?
Hyperpolarization is the process of the membrane potential becoming more negative, moving away from 0 mV.
p.4
Effect of high and low plasma potassium on threshold potential
What is the effect of high plasma potassium on threshold potential?
High plasma potassium (hyperkalemia) lowers the threshold potential, making it easier to generate an action potential.
p.10
Action potential basics
What are the basic characteristics of an action potential?
All-or-none event, constant amplitude, initiated by depolarization, involves changes in permeability, relies on voltage-gated ion channels.
p.16
Action potential basics
What is the significance of the overshoot in the action potential graph?
The overshoot represents the phase where the membrane potential becomes positive due to high Na+ conductance.
p.17
Action potential basics
How are compound action potentials measured percutaneously?
From nerves that are close to the surface, such as the ulnar nerve.
p.25
Action potential basics
What happens when multiple stimuli are applied to a neuron?
The responses summate, resulting in a summed response.
p.9
Effect of low plasma calcium on threshold potential
How does treatment with calcium help in hyperkalemia?
It reestablishes a 15 mV difference between Vm and threshold potential, reducing arrhythmias.
p.27
Transmission at a Chemical Synapse
What is the result of depolarization in the postsynaptic neuron?
The opening of voltage-gated Na+ channels and the generation of an action potential (AP).
p.14
Action potential basics
What occurs during the overshoot phase of an action potential?
During the overshoot phase, the membrane potential becomes positive.
p.14
Ion channels and their permeability
What happens to K+ conductance during the action potential?
K+ conductance increases after the peak of the action potential.
p.11
Action potential basics
Do action potentials summate?
No, action potentials do not summate.
p.11
Action potential basics
What is the formula for the conduction velocity of unmyelinated fibers?
Square root of unmyelinated fiber diameter = velocity in m/s.
p.13
Ion channels and their permeability
What are the two gating transitions in ion channels?
Activation (opening of the channel when the membrane is depolarized) and deactivation (closure of the channel when the membrane repolarizes).
p.4
Effect of high and low plasma potassium on membrane potential
What is the effect of high plasma potassium on membrane potential?
High plasma potassium (hyperkalemia) decreases the membrane potential, making it less negative.
p.30
Action potential basics
What is the main event in Phase 3 of the ventricular action potential?
Outward K+ current (repolarization).
p.10
Action potential basics
What does it mean for an action potential to propagate?
It is conducted without decrement, meaning it is an 'active' membrane event.
p.10
Action potential basics
What type of ion channels do action potentials rely on?
Voltage-gated ion channels.
p.14
Ion channels and their permeability
What is the state of the Na+ activation gate at resting membrane potential?
The Na+ activation gate is closed at resting membrane potential (-90 mV).
p.24
Transmission at a Chemical Synapse
What effect do excitatory transmitters have on the membrane?
They depolarize the membrane.
p.14
Ion channels and their permeability
What is the state of the K+ channel at resting membrane potential?
The K+ channel is closed at resting membrane potential (-90 mV).
p.11
Action potential basics
Can action potentials be induced by extrinsic stimulation?
Yes, they can be induced in nerve and muscle by extrinsic (percutaneous) stimulation.
p.13
Ion channels and their permeability
What are ion channels usually selectively permeable to?
Specific ions or classes of ions.
p.4
Action potential basics
What is overshoot in the context of membrane potential?
Overshoot refers to the membrane potential becoming positive, moving above 0 mV.
p.4
Effect of high and low plasma potassium on threshold potential
What is the effect of low plasma potassium on threshold potential?
Low plasma potassium (hypokalemia) raises the threshold potential, making it harder to generate an action potential.
p.30
Ion channels and their permeability
How does the relative potassium conductance change during the ventricular action potential?
It increases during Phase 1 and Phase 3, and decreases during Phase 2.
p.10
Action potential basics
What is meant by 'all-or-none' in the context of action potentials?
An action potential either occurs fully or not at all, needing to reach a threshold to be initiated.
p.14
Ion channels and their permeability
What is the ratio of Na+ to K+ conductance during the peak of the action potential?
The ratio of Na+ to K+ conductance is highest during the peak of the action potential.
p.29
Action potential basics
What effect do excitatory synapses have on the postsynaptic cell?
They depolarize the postsynaptic cell and enhance excitability.
p.13
Ion channels and their permeability
What are non-selective cation channels?
Channels that are selective only for cations (Na, K, and Ca) over anions (e.g., Cl-).
p.4
Action potential basics
What is repolarization?
Repolarization is the process of the membrane potential returning towards the resting potential after depolarization.
p.30
Action potential basics
What occurs during Phase 0 of the ventricular action potential?
Inward Na+ current (depolarization).
p.30
Ion channels and their permeability
What is the role of calcium conductance during the ventricular action potential?
It increases during Phase 2 (plateau).
