Can summation occur in action potentials?
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No, summation is not possible in action potentials.
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Can summation occur in action potentials?
No, summation is not possible in action potentials.
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).
What does the selectivity filter in voltage gated Na+ channels consist of?
Negatively charged amino acids such as glutamate.
Which ions' permeability increase is associated with the sympathetic mechanism in the SA node action potential?
Na+ and Ca++ ions.
What is the resting membrane potential for erythrocytes?
−8 to −12 mV
What initiates the propagation of an action potential?
Opening of Na+ channels generates local current that depolarizes adjacent membrane, opening more Na+ channels.
How do calcium ions affect Na channels?
Calcium ions bind to the exterior surfaces of the voltage-gated sodium channel.
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.
How is information encoded in action potentials?
The frequency of action potentials encodes information, while the amplitude of action potentials remains constant.
What is the resting membrane potential (Vm) when serum K+ is 6 mEq/L?
-90 mV
Which way do Na+ ions diffuse when permeability increases?
Into the cell
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.
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.
What is the resting membrane potential (Vm) when serum K+ is 4 mEq/L?
-90 mV
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.
What happens to Na channels during the absolute refractory period?
Na channels are voltage inactivated.
How does myelination affect the conduction of action potentials?
Myelination allows action potentials to jump between nodes of Ranvier, increasing conduction speed.
What is the main ion movement in Phase 3 of the sinoatrial node action potential?
Outward K+ current.
How does the strength of the stimulus affect an electrotonic potential?
An electrotonic potential is proportional to stimulus strength (graded).
How is an action potential propagated?
An action potential is propagated unchanged in magnitude.
At what membrane potential does the threshold for the sinoatrial node action potential occur?
Approximately -40 mV.
What type of disease is Multiple Sclerosis (MS)?
MS is an immune-mediated inflammatory demyelinating disease of the CNS.
What happens to the membrane potential during Phase 3 of the sinoatrial node action potential?
It repolarizes due to the outward K+ current.
What is the female-to-male ratio for Multiple Sclerosis incidence?
The female-to-male ratio is 2:1.
Can summation occur in electrotonic potentials?
Yes, electrotonic potentials exhibit summation.
What does the ratio of conductances graph represent?
The ratio of Na+ conductance to K+ conductance during an action potential.
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.
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.
What is the threshold potential when serum K+ is 4 mEq/L?
15 mV
Why does an increase in extracellular potassium concentration make the cell more excitable?
Because the resting membrane potential is closer to the threshold potential.
Why do nonmyelinated axons conduct action potentials more slowly?
In nonmyelinated axons, action potentials must propagate continuously along the entire length of the axon.
What is the equilibrium potential for potassium (E_K)?
-94 mV
What is one benefit of saltatory conduction in terms of speed?
It increases the velocity of action potential propagation.
What is the resting membrane potential for skeletal muscle fibers?
−85 to 95 mV
What is the resting membrane potential for neurons?
−60 to −70 mV
Why can tetany in respiratory muscles be lethal?
Because it can impair breathing.
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).
What type of channels have a selectivity filter?
Voltage Gated Na+ Channels.
What is the resting membrane potential for smooth muscle fibers?
−50 to −60 mV
What is the net driving force on Na+ ions under normal conditions?
135 mV
Which way do K+ ions diffuse when permeability increases?
Out of the cell
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.
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.
Why do action potentials only occur at the nodes during saltatory conduction?
Because Na+ channels are concentrated at the nodes.
Which specific amino acid is mentioned as part of the selectivity filter in voltage gated Na+ channels?
Glutamate.
What is the net driving force on K+ ions under normal conditions?
20 mV
What is the resting membrane potential for photoreceptor cells in the dark?
−40 mV
What are the two types of synapses?
Excitatory and Inhibitory
What occurs during the 'Stimulated' phase of action potential propagation?
Local depolarization occurs due to the opening of Na+ channels.
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.
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.
What is the relative refractory period?
A period during which a greater than normal stimulus is required to elicit an action potential (AP).
What is the term for the jumping of action potentials between nodes of Ranvier in myelinated axons?
Saltatory conduction.
What characterizes Phase 4 of the sinoatrial node action potential?
Slow depolarization due to inward Na+ current.
What is the prevalence of Multiple Sclerosis in the US?
About 1 person per 1000 in the US is thought to have the disease.
What is the equilibrium potential for sodium (E_Na)?
+61 mV
How does saltatory conduction contribute to energy conservation?
By reducing the amount of ion exchange needed along the axon, thus conserving energy.
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.
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.
What do most synapses involve?
Transmitter substances
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.
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.
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.
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.
How do refractory periods affect the frequency of action potentials?
Refractory periods limit the maximum frequency of action potentials.
What occurs during Phase 0 of the sinoatrial node action potential?
Depolarization due to inward Ca++ current.
Where do action potentials (APs) occur during saltatory conduction?
At the nodes of Ranvier.
What is the charge of the amino acids in the selectivity filter of voltage gated Na+ channels?
Negatively charged.
What is the typical voltage range for the SA node action potential?
From -80 mV to 0 mV.
What is the point of communication between neurons called?
Synapse
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.
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).
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.
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.
What is the threshold potential when serum K+ is 6 mEq/L?
11 mV
What is the difference in conduction velocity between nonmyelinated and myelinated axons?
Myelinated axons have a faster conduction velocity compared to nonmyelinated axons.
What structural feature of myelinated axons contributes to their increased conduction velocity?
The presence of myelin sheaths and nodes of Ranvier.
What is the significance of the inward Ca++ current in the sinoatrial node action potential?
It causes depolarization during Phase 0.
Which demographic has the highest incidence of Multiple Sclerosis?
Whites of northern European descent have the highest incidence.
What does each peak in a compound action potential recording represent?
A set of axons with similar conduction velocity.
From where are compound action potentials recorded?
From nerve trunks.
What is seen as a small (mV) voltage signal on the body surface?
The passage of action potentials in all axons of nerves.
What is the effect of 'local current flow' in a neuron?
It depolarizes adjacent regions of a neuron.
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.
What is a ligand?
A ligand is any substance that binds to a receptor.
How are receptors often named and classified?
Receptors are often named and classified largely by reference to the ligand.
How are receptors often subdivided?
Receptors are often subdivided by reference to ligands.
Which substance stimulates nicotinic (nACh) receptors?
Nicotine.
What effect does increasing the permeability to K+ ions have on the SA node action potential?
It causes the parasympathetic mechanism effect.
What is the role of the selectivity filter in voltage gated Na+ channels?
To selectively allow Na+ ions to pass through the channel.
What is the resting membrane potential for astrocytes?
−80 to −90 mV
What is the most common cause of muscle tetany?
Hypocalcemia.
What is the resting membrane potential for photoreceptor cells in the light?
−70 mV
What is an axo-dendritic synapse?
A synapse between the axon of one neuron and the dendrite of another neuron
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.
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.
What is the absolute refractory period?
A period during which an action potential (AP) is not possible due to voltage inactivation of Na channels.
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.
How does the strength of the stimulus affect an action potential?
An action potential is independent of stimulus strength (all or none).
How is an electrotonic potential propagated?
An electrotonic potential is not propagated but decremental with distance.
What is the role of the inward Na+ current in the sinoatrial node action potential?
It contributes to the slow depolarization during Phase 4.
What happens to the Na+ conductance during the initial phase of an action potential?
Na+ conductance increases rapidly.
How does K+ conductance change during an action potential?
K+ conductance increases after the peak of the action potential and remains elevated during repolarization.
How are local potentials graded?
A bigger stimulus results in a bigger response.
What specialized structures do neurons use to communicate?
Synapses.
How do neurotransmitters travel across the synaptic cleft?
They diffuse across the synaptic cleft, which is less than 20 nm wide.
What is the initial treatment for hyperkalemia?
Intravenous administration of calcium.
Why do patients with Multiple Sclerosis often have difficulty describing their symptoms?
Because the symptoms can resolve and reoccur, making them difficult to describe.
What happens when the resolution of neurologic deficits in Multiple Sclerosis becomes incomplete or too frequent?
The diagnostic dilemma begins.
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.
How does high potassium (K+) affect the membrane potential (Vm)?
High K+ makes Vm less negative, moving it from −90 mV to −80 mV.
What happens when Ca2+ enters the presynaptic neuron?
It causes the release of neurotransmitters from vesicles.
What happens when neurotransmitters bind to receptors on the postsynaptic neuron?
It causes the opening of receptor-operated channels, leading to depolarization.
What determines whether the postsynaptic membrane is hyperpolarized or depolarized?
The selectivity of the channels for particular ions.
What ions are involved in the transmission at a chemical synapse?
Na+, K+, and Ca2+.
What are the two types of acetylcholine (ACh) receptors?
Nicotinic (nACh) and muscarinic (mACh) receptors.
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).
How is information coded in action potentials?
Information is coded by frequency, not amplitude.
What effect do inhibitory synapses have on the postsynaptic cell?
They hyperpolarize the postsynaptic cell and depress excitability.
What ions are excitatory synapses permeable to?
Cations (Na+, K+, and Ca2+).
What is an excitatory postsynaptic potential (EPSP)?
A depolarization of the postsynaptic cell that enhances excitability.
What do the terms 'gate' and 'gating' refer to in ion channels?
Transitions between different states of the channel protein.
What is the threshold potential?
The threshold potential is the membrane potential at which an action potential is generated.
What happens during Phase 2 of the ventricular action potential?
Inward Ca++/Na+ current and decreased outward K+ current (plateau).
What is an action potential?
A regenerating depolarization of membrane potential that propagates along an excitable membrane.
What changes occur during an action potential?
Changes in permeability.
What are some common initial symptoms of Multiple Sclerosis?
Paresthesias of a hand that resolves, followed by weakness in a leg or visual disturbances.
How is conduction velocity calculated?
By dividing the distance between R1 and R3 by the time taken to traverse that distance (distance/time = velocity).
What is a key characteristic of local potentials regarding refractoriness?
Local potentials do not induce refractoriness.
What happens to the waveform as recordings are made further from the site of stimulation?
The waveform develops into several discrete peaks.
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.
In fast synapses, what do transmitter substances bind to on the postsynaptic cell?
Receptors to directly open ion channels (ligand-gated).
What happens to Na+ conductance during the action potential?
Na+ conductance increases rapidly during the action potential.
Towards what will the membrane potential move in the postsynaptic cell?
Towards the equilibrium potential for the permeant ion(s).
What happens when synaptic responses reach the threshold?
They initiate an action potential.
What is the typical threshold voltage for an action potential?
Usually 15 mV positive to resting potential.
Do action potentials have constant amplitude?
Yes, action potentials have constant amplitude.
What is the formula for the conduction velocity of myelinated fibers?
Myelinated fiber diameter (in mm) × 4.5 = velocity in m/s.
What ions do Na channels pass?
Only Na ions.
What triggers most voltage-gated channels to open?
Depolarization.
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.
What characterizes Phase 1 of the ventricular action potential?
Outward K+ current (early repolarization).
Do action potentials summate?
No, they have a constant amplitude and do not summate.
Why do patients with Multiple Sclerosis frequently not bring their complaints to doctors?
Because the symptoms often resolve on their own.
What occurs during the positive afterpotential phase?
The membrane potential remains slightly above the resting potential due to the delayed closing of K+ channels.
Why is hyperkalemia considered one of the deadliest electrolyte disorders?
Because it can cause deadly cardiac arrhythmias.
What triggers the opening of voltage-gated Ca2+ channels in the presynaptic neuron?
The arrival of an action potential (AP).
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.
Why are these potentials called 'electrotonic' or 'local' potentials?
Because the effect is 'local' to the stimulus.
Which substances are considered ligands?
Acetylcholine, Norepinephrine, Epinephrine, Serotonin (5-HT), Dopamine, Glycine, Glutamate, Adenosine.
What are 'physiological' ligands?
Acetylcholine and norepinephrine are 'physiological' ligands, i.e., provided by the body.
What can subthreshold synaptic responses do?
They can summate with others.
How are action potentials initiated?
By depolarization.
What are examples of inhibitory neurotransmitters?
GABA_A and Glycine.
What determines the permeability of the axon membrane to ions?
The number of open channels.
What is an inhibitory postsynaptic potential (IPSP)?
A hyperpolarization of the postsynaptic cell that depresses excitability.
What is depolarization?
Depolarization is the process of the membrane potential becoming more positive, moving towards 0 mV.
What is the effect of low plasma potassium on membrane potential?
Low plasma potassium (hypokalemia) increases the membrane potential, making it more negative.
What is Phase 4 of the ventricular action potential known as?
Resting potential.
What does it mean for a membrane to be excitable?
It is capable of generating action potentials.
What is the approximate velocity of an action potential?
Approximately 60 m/s.
What does the first signal to arrive at a distant recording site indicate?
It has traveled the fastest.
What is the range of conduction velocities for action potentials?
From 0.5 to ~100 m/s.
What is the relationship between Na+ and K+ conductance during the repolarization phase?
During repolarization, Na+ conductance decreases while K+ conductance increases.
What is the threshold potential in the context of hyperkalemia?
The threshold potential is −75 mV.
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.
What happens to the permeability of the postsynaptic membrane when transmitter substances bind to receptors?
The permeability to ions is increased.
How long does it take for neurotransmitters to diffuse across the synaptic cleft?
Approximately 0.5 milliseconds.
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).
What type of events are action potentials?
All-or-none events.
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.
What determines the conduction velocity of action potentials in fibers?
The diameter of the fiber; larger diameter fibers conduct faster than smaller fibers.
What is the equilibrium potential of excitatory synapses?
Approximately 0 mV.
What ions do Ca channels pass and why are they important?
Only Ca ions; they are important in synaptic transmission.
What is hyperpolarization?
Hyperpolarization is the process of the membrane potential becoming more negative, moving away from 0 mV.
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.
Which ion current is shown as a dashed line during Phase 2?
Na+ current.
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.
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.
How are compound action potentials measured percutaneously?
From nerves that are close to the surface, such as the ulnar nerve.
What happens when multiple stimuli are applied to a neuron?
The responses summate, resulting in a summed response.
What causes the release of transmitter in the presynaptic cell?
An action potential.
How does treatment with calcium help in hyperkalemia?
It reestablishes a 15 mV difference between Vm and threshold potential, reducing arrhythmias.
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).
What occurs during the overshoot phase of an action potential?
During the overshoot phase, the membrane potential becomes positive.
What happens to K+ conductance during the action potential?
K+ conductance increases after the peak of the action potential.
Which substance stimulates muscarinic (mACh) receptors?
Muscarine.
Do action potentials summate?
No, action potentials do not summate.
What is the formula for the conduction velocity of unmyelinated fibers?
Square root of unmyelinated fiber diameter = velocity in m/s.
What ions do K channels pass?
Only K ions.
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).
What is the effect of high plasma potassium on membrane potential?
High plasma potassium (hyperkalemia) decreases the membrane potential, making it less negative.
What is the main event in Phase 3 of the ventricular action potential?
Outward K+ current (repolarization).
What does it mean for an action potential to propagate?
It is conducted without decrement, meaning it is an 'active' membrane event.
What type of ion channels do action potentials rely on?
Voltage-gated ion channels.
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).
What effect do excitatory transmitters have on the membrane?
They depolarize the membrane.
What is the state of the K+ channel at resting membrane potential?
The K+ channel is closed at resting membrane potential (-90 mV).
Can action potentials be induced by extrinsic stimulation?
Yes, they can be induced in nerve and muscle by extrinsic (percutaneous) stimulation.
What ions are inhibitory synapses permeable to?
Anions (Cl-).
What are examples of excitatory neurotransmitters?
nAChR and Glutamate.
What are ion channels usually selectively permeable to?
Specific ions or classes of ions.
What ions do Cl channels pass?
Only Cl ions.
What is overshoot in the context of membrane potential?
Overshoot refers to the membrane potential becoming positive, moving above 0 mV.
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.
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.
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.
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.
What is the equilibrium potential of inhibitory synapses?
Approximately -90 mV.
What effect do excitatory synapses have on the postsynaptic cell?
They depolarize the postsynaptic cell and enhance excitability.
What are non-selective cation channels?
Channels that are selective only for cations (Na, K, and Ca) over anions (e.g., Cl-).
What is repolarization?
Repolarization is the process of the membrane potential returning towards the resting potential after depolarization.
What occurs during Phase 0 of the ventricular action potential?
Inward Na+ current (depolarization).
What is the role of calcium conductance during the ventricular action potential?
It increases during Phase 2 (plateau).
What initiates an action potential?
Depolarization.
