In which phase of the action potential is the conductance velocity of potassium least?
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In which phase of the action potential is the conductance velocity of potassium least?
Phase 4.
What is the Goldman equation also known as?
The Goldman - Hodgkin - Katz equation.
What is the value calculated by the Goldman equation in this context?
86 mV.
What happens to membrane potential as the amount of separated charges increases?
The membrane potential increases.
What does the Nernst Equation calculate?
The equilibrium potential for a specific ion.
What is responsible for the potential across a membrane?
Unbalanced charges that accumulate in a thin layer along opposite surfaces of the membrane.
What are some functions that action potentials are important for?
Nerve traffic, muscle contraction, hormone release, G.I. secretions, and cognitive thought.
What does the equilibrium potential represent?
The charge that the membrane would have if only that ion could cross the membrane.
Which senses depend on action potentials for information transmission to the brain?
Sight, hearing, and touch.
What happens when positive and negative charges are distributed equally across the membrane?
No membrane potential exists.
What type of stimuli causes the generation of an action potential?
Threshold stimuli (Graded Potential).
What is an action potential?
A transient change in the membrane potential that conveys information within the nervous system.
What causes repolarization of the neuronal cell membrane when a nerve is stimulated?
Increase in outward permeability of K+ ion.
What occurs when opposite charges are separated across a membrane?
Membrane potential exists.
What are graded potentials?
Changes in membrane potential that vary in size and are conducted with decrement.
What are refractory periods in relation to action potentials?
Times when it is either impossible or more difficult than normal to generate a second action potential.
What are receptor (generator) potentials?
Graded potentials in response to stimuli from sensory receptors.
Which types of cells generate action potentials?
Electrically excitable cells, such as nerve and muscle cells.
How is the conduction of graded potentials characterized?
By decrement, meaning the conduction magnitude falls off the further you get from the point of origin.
What stimulates the generation of an action potential?
A change in membrane potential due to the flow of current in and out of the cell.
What types of receptors respond to stimuli that generate receptor potentials?
Mechanoreceptors, thermoreceptors, nociceptors, chemoreceptors, and electromagnetic receptors.
What is the electrical resistance of the lipid bilayer?
It has a high electrical resistance, meaning charged particles do not move easily across it.
What happens if a graded potential reaches the threshold?
An action potential is generated, sending sensory information to the spinal cord and brain.
What is the diffusion potential level across a membrane that opposes the net diffusion of a particular ion called?
Nernst potential.
What is a graded potential?
A potential change of variable amplitude and duration that is conducted decrementally; it has no threshold or refractory period.
What are the two gradients responsible for the movement of ions across the membrane?
Electrical gradients and chemical (concentration) gradients.
What does the lipid bilayer separate?
Two very conductive (salty) solutions.
What is the graded potential called when it occurs in response to stimuli?
Receptor potential.
What is the End Plate Potential (EPP)?
A post synaptic potential at the neuromuscular junction that is always stimulatory.
What type of potential is established across a membrane when it is permeable to potassium ions?
Diffusion potential.
What are graded potentials that develop on the postsynaptic membrane called?
Postsynaptic potentials.
What is hyperkalemia?
An electrolyte disorder characterized by elevated potassium levels in the blood.
What characterizes an action potential?
A brief all-or-none depolarization of the membrane, reversing polarity in neurons; it has a threshold and refractory period and is conducted without decrement.
What does the Nernst potential relate to?
The concentration difference of a particular ion.
What does the electrical gradient influence in membrane potentials?
The movement of charged ions across the membrane.
What happens to the EPP if generated by an action potential (AP) in the innervating α motor neuron?
It reaches threshold.
What types of stimuli can graded potentials be during synaptic transmission?
They can be stimulatory (EPSP) or inhibitory (IPSP).
What happens to charge in graded potentials due to 'leaky' channels?
Charge is lost across the membrane, causing the magnitude of the potential to decrease with distance from the site of origin.
How thick is the lipid bilayer?
About 5 nm.
What ions can pass through the membrane in this scenario?
Potassium ions.
What is a synaptic potential?
A graded potential change produced in the postsynaptic neuron in response to the release of a neurotransmitter by a presynaptic terminal; it may be depolarizing (EPSP) or hyperpolarizing (IPSP).
What are graded potentials?
Changes in membrane potential that vary in size and are not all-or-nothing.
What effect does hyperkalemia have on nerve excitability?
Nerve is more excitable.
What is one characteristic of graded potentials?
They are the only type of communication by some neurons.
What is an action potential?
A rapid change in membrane potential that propagates along the membrane of a neuron.
What generates action potentials?
Graded potentials that reach threshold.
What happens if graded potentials reach the threshold?
An action potential develops.
Is the End Plate Potential (EPP) excitatory or inhibitory?
It is always stimulatory.
What is the role of the chemical gradient in membrane potentials?
It drives the movement of ions based on their concentration differences.
What is a receptor potential?
A graded potential produced at the peripheral endings of afferent neurons in response to a stimulus.
What is established when a nerve fiber membrane is permeable only to sodium ions?
A diffusion potential.
What is potential in the context of voltage?
The voltage difference between two points.
How do graded potentials function in terms of distance?
They can function as signals over very short distances.
What is the difference between EPSP and IPSP?
EPSP is a depolarizing synaptic potential, while IPSP is a hyperpolarizing synaptic potential.
What cannot pass through the membrane in this scenario?
Anions.
What does it mean that graded potentials are 'graded'?
Their magnitude can vary with the magnitude of the stimulus.
What property of the lipid bilayer allows it to store a large amount of charge?
Its thinness allows for high capacitance.
How can the Na+/K+ ATPase pump be neutral regarding membrane charge?
By moving equal numbers of K+ in and Na+ out.
How do graded potentials differ from action potentials?
Graded potentials can vary in magnitude, while action potentials are uniform and all-or-nothing.
What role do graded potentials play in neurons?
They are important for the initiation and integration of long-distance signals.
Which option describes the effect of hyperkalemia on nerve threshold potential?
Nerve becomes more excitable.
What does it mean for a cell to have a resting membrane potential difference?
It refers to the voltage difference across the cell membrane when the cell is not actively transmitting signals.
What happens to membrane polarity during an action potential?
It reverses, resulting in complete depolarization.
What are the types of action potentials?
There are different types based on the stimulus and the resulting response, such as graded potentials leading to action potentials.
What does the relative refractory period correspond to in action potentials?
The positive after potential period.
What is the role of graded potentials in the heart?
Graded potentials can potentially induce a true cardiac action potential.
What is a pacemaker potential?
A spontaneously occurring graded potential change that occurs in certain specialized cells.
What is the average duration of an action potential?
1 to 5 milliseconds.
What is the electrogenic nature of the Na+/K+ ATPase pump?
It contributes to inside-negativity by moving 3 Na+ out for every 2 K+ in.
What does membrane potential refer to?
The voltage difference between the inside and outside of a cell.
What ions are involved in the establishment of a diffusion potential in this context?
Sodium ions.
What happens with small differences in the electrical balance of charges inside the cell?
They easily attract opposite charges to the outside of the cell.
How are action potentials propagated?
Without decrement.
What are the two types of graded events?
Hypopolarizing (depolarizing) and hyperpolarizing.
What causes graded potentials?
They are caused by the opening of ion channels in response to stimuli.
What is the potential difference required for a normal mammalian nerve fiber?
About 94 millivolts.
How do changes in ion permeability affect membrane potential?
Changes in ion permeability can lead to depolarization or hyperpolarization of the membrane potential, depending on which ions are more permeable.
How far do graded potentials typically die out from their origin?
In 1 - 2 mm of the origin.
What initiates an action potential?
A sufficient depolarization of the neuron's membrane.
Why is it more difficult to generate a second action potential during the relative refractory period?
Due to the hyperpolarization of the cell.
What is the answer to question 1?
D
What is threshold potential?
The membrane potential at which an action potential is initiated.
What are graded potentials?
Changes in membrane potential that vary in size and are not all-or-nothing.
What does the Na+/K+ ATPase pump maintain?
The concentration gradients for the two most important ions that determine the membrane potential.
What specialized cells are involved in the pacemaker potential?
Specialized cells in the cardiac pacemaker region (SA node).
Do action potentials have a specific size and shape?
Yes, they have a specific size and shape.
What is equilibrium potential?
The voltage difference across a membrane that produces a flux of a given ion species equal but opposite to the flux due to the concentration gradient of that same ion species.
What happens to the membrane potential when it becomes permeable to sodium ions?
It generates a diffusion potential due to sodium ion movement.
What is constant along a nerve fiber during action potentials?
The size and shape of the action potential.
What happens during hypopolarizing graded potentials?
There is a decrease in potential difference.
What is the effect of distance on graded potentials?
Graded potentials decrease in amplitude as they spread away from the point of origin.
What is the charge inside the nerve fiber in this scenario?
Negativity inside.
What is the role of ion channels in action potentials?
Ion channels open and close to allow the flow of ions, which changes the membrane potential and propagates the action potential.
What happens to voltage-gated channels if a cell membrane is maintained above threshold voltage?
They become inactivated and cannot generate action potentials.
What is the answer to question 2?
C
How do graded potentials differ from action potentials?
Graded potentials can vary in magnitude, while action potentials are uniform and all-or-nothing.
How does the duration of graded potentials compare to action potentials?
Graded potential duration varies with initiating conditions, while action potential duration is constant for a given cell type under constant conditions.
Is the duration of an action potential the same for specific tissues?
Yes, it is always the same for a specific tissue.
What is a generator potential?
A change in membrane potential that occurs in response to a stimulus at a sensory receptor.
What is resting membrane potential?
The steady transmembrane potential of a cell that is not producing an electric signal.
What type of ion channels do pacemaker cells have?
Leaky ion channels.
What happens when the ionic composition of the medium is equilibrated with the intracellular concentration in the giant squid axon?
No more action potentials are seen upon stimulation.
What is the role of graded potentials in neurons?
They can lead to action potentials if the threshold is reached.
What is voltage inactivation?
It is the state where voltage-gated channels are not reset and remain inactivated, preventing action potential generation.
What factors influence the size of a graded potential?
The strength of the stimulus and the type of ion channels activated.
Why does the resting membrane potential of most cells approximate the Nernst potential for potassium (K)?
Because potassium ions (K+) are the most permeable ions at rest, influencing the membrane potential significantly.
What is the answer to question 3?
B
What types of changes can graded potentials cause?
Graded potentials can be either a depolarization or a hyperpolarization.
What are the properties of generator potentials?
They are graded, meaning their amplitude varies with the strength of the stimulus.
What influences the time frame of action potentials?
Specific transport protein cycle times.
What is the likely cause of no response after equilibrating ion concentrations in the axon?
Increased permeability for Na+ is not achieved, leading to no action potential generation.
What initiates the action potential in a neuron?
A depolarization that reaches the threshold potential.
What is a graded potential?
A change in membrane potential that varies in size depending on the strength of the stimulus.
What occurs during accommodation to slow depolarization?
Voltage-gated channels do not respond, and no action potential occurs.
What is the answer to question 4?
E
Where do graded potentials typically occur?
In the dendrites and cell body of neurons.
What type of change does an action potential cause?
An action potential is only a depolarization.
What is an action potential?
A rapid, temporary change in the membrane potential of a neuron.
How does transduction occur in sensory receptors?
Transduction converts a stimulus into an electrical signal, typically a generator potential.
What is the threshold potential typically around?
Approximately -55 mV.
What does the term 'absolute refractory period' refer to?
A phase during which no new action potentials can be generated, regardless of stimulus strength.
What is a subthreshold response in graded potentials?
A local response that does not reach the threshold for action potential generation.
What is a postsynaptic potential?
A graded potential that occurs in the dendrites or cell body of a neuron in response to a neurotransmitter.
What is the first stage of the action potential?
Resting stage.
What happens to graded potentials as they move away from the stimulus site?
They decrease in amplitude due to passive current flow.
What happens when a generator potential reaches a certain threshold?
It can trigger an action potential in the sensory neuron.
What is the answer to question 5?
C
What initiates graded potentials?
Graded potentials are initiated by environmental stimuli (receptors), neurotransmitters (synapses), or spontaneously.
What is the effect of slow depolarization on action potential generation?
It prevents the generation of action potentials due to unresponsive voltage-gated channels.
What triggers the generation of an action potential?
A depolarization that reaches a threshold level.
What is responsible for cardiac automaticity?
Graded potential.
What ions are primarily involved in the conductance during an action potential?
Potassium (K) and Sodium (Na).
What does RMP stand for in neurophysiology?
Resting Membrane Potential.
What happens during the depolarization phase of an action potential?
Sodium channels open, allowing Na+ ions to flow into the cell.
What is the normal resting membrane potential for nerve cells?
-90 mV.
What does it mean that graded potentials are local?
Changes in membrane potential are confined to relatively small regions of the plasma membrane.
What is the relationship between stimulus intensity and generator potential?
Higher stimulus intensity results in a larger generator potential.
What is the difference between absolute and relative refractory periods?
During the absolute refractory period, no action potentials can occur; during the relative refractory period, a stronger-than-normal stimulus can trigger an action potential.
What are receptor potentials?
Graded potentials that occur in sensory receptors.
What initiates action potentials?
Action potentials are initiated by a graded potential.
What are the phases of an action potential?
Depolarization, repolarization, and hyperpolarization.
What is an action potential?
A rapid change in membrane potential that propagates along the axon of a neuron.
What happens to sodium conductance during the depolarization phase of an action potential?
Sodium conductance increases rapidly.
What is bioelectricity in the context of neurons?
Bioelectricity refers to the electrical properties and activities of neurons that enable communication within the nervous system.
What is the typical value of resting membrane potential in neurons?
Approximately -70 mV.
What is required for the generation of an action potential?
Specific voltage-gated ion channels.
What happens during the depolarization stage of the action potential?
Threshold for voltage-gated Na+ channels is exceeded, leading to Na+ influx.
What is the role of potassium channels during the action potential?
They open during repolarization, allowing K+ ions to exit the cell.
What is the primary purpose of recording membrane potentials?
To measure the electrical activity across a cell membrane.
What does it mean that graded potentials are graded?
It refers to the magnitude of the potential change, indicating that the signal can be reinforced.
What could be a consequence of increased action potential amplitude?
It could lead to stronger signals but does not explain the lack of response after ion concentration equilibration.
What are generator potentials?
Graded potentials that occur in sensory neurons.
What mechanisms do graded potentials depend on?
Graded potentials depend on ligand-sensitive channels or other chemical or physical changes.
What role do sodium (Na+) ions play in action potentials?
They rush into the neuron during depolarization, causing the membrane potential to become more positive.
What ions are primarily involved in generating an action potential?
Sodium (Na+) and potassium (K+).
What are the three factors that affect diffusion potential when the membrane is permeable to several different ions?
What role does potassium conductance play during the repolarization phase of an action potential?
Potassium conductance increases, allowing K+ to exit the cell.
What primarily determines the resting membrane potential?
The distribution of ions across the cell membrane, particularly sodium (Na+) and potassium (K+).
What is the resting membrane potential for heart pacemaker cells?
-60 mV.
What causes action potentials?
Rapid changes in ion conductance.
What is the refractory period?
The time during which a neuron cannot fire another action potential.
What equipment is typically used to record membrane potentials?
Microelectrodes and an oscilloscope or a voltmeter.
How does the speed of conduction of action potentials relate to ion concentration?
The speed of conduction can be affected by ion concentration, but in this case, the lack of response is due to ion equilibration.
How do graded potentials differ?
They have different names depending on the type of stimulus and location where they occur.
What mechanisms do action potentials depend on?
Action potentials depend on voltage-gated channels.
What happens during repolarization?
Potassium (K+) ions exit the neuron, restoring the negative membrane potential.
What occurs during the depolarization phase of an action potential?
Sodium channels open, allowing Na+ to flow into the neuron, making the inside more positive.
How does the polarity of the electrical charge of each ion affect diffusion potential?
It influences the movement of ions across the membrane based on their charge.
What is the first phase of action potential?
Depolarization.
What is the typical value of resting membrane potential in neurons?
Typically around -70 mV.
How does the change in sodium and potassium conductance affect the membrane potential?
Increased Na+ conductance depolarizes the membrane, while increased K+ conductance repolarizes it.
What is a receptor in the context of sensory modalities?
A specialized cell or distal portion of a neuron that responds to specific sensory modalities like touch, pressure, cold, light, or sound, and converts it to an electrical signal.
Which statement correctly describes graded potentials and action potentials?
B. Graded potentials are proportional to the magnitude of the stimulus, whereas action potentials are 'all-or-none.'
Which ion has a higher concentration inside the cell at rest?
Potassium (K+).
What occurs during the repolarization stage of the action potential?
K+ outflow through voltage-gated K+ channels, moving the membrane potential back toward RMP.
Where do action potentials occur?
Only on regions of cell membranes that are electrically excitable.
What is the significance of the all-or-nothing principle in action potentials?
Once the threshold is reached, an action potential will occur fully or not at all.
What is the first step in setting up for recording membrane potentials?
Insert a microelectrode into the cell.
What is the refractory period?
The time during which a neuron cannot fire another action potential.
What happens during the repolarization phase of an action potential?
Potassium channels open, allowing K+ to flow out of the neuron, restoring the negative membrane potential.
What occurs during the depolarization phase?
Sodium channels open, allowing Na+ ions to enter the neuron.
What role does membrane permeability (P) play in diffusion potential?
It determines how easily ions can pass through the membrane.
What is the effect of sodium channel inactivation during an action potential?
It prevents further influx of Na+, contributing to repolarization.
What types of sensory modalities can receptors respond to?
Touch, pressure, cold, light, or sound.
What does the Nernst equation calculate?
The Nernst equation calculates the equilibrium potential for a specific ion based on its concentration gradient across the membrane.
What is true about graded potentials?
D. Graded potentials are always decremental, whereas action potentials are always non-decremental.
Which ion has a higher concentration outside the cell at rest?
Sodium (Na+).
What is the resting membrane potential for skeletal muscle cells?
-83 mV.
What occurs during the hyperpolarization phase?
The membrane potential becomes more negative than the resting potential.
What is the significance of the reference electrode in membrane potential recording?
It provides a stable reference point for measuring the potential difference.
How do action potentials vary among different cell types?
They generally have a standard size and shape for a specific cell type.
What is the significance of the threshold potential?
It is the critical level that must be reached for an action potential to occur.
How is an action potential propagated along a nerve?
By the sequential opening and closing of ion channels along the axon.
What is the second phase of action potential?
Repolarization.
Why are the concentrations (C) of ions important for diffusion potential?
They dictate the gradient that drives the movement of ions across the membrane.
What happens to the magnitude of action potential as it travels away from the point of generation?
E. Magnitude of action potential is in a gradual decreasing order as it travels away from the point of generation.
What is the electrical signal generated by receptors called?
Generator or receptor potential.
What factors influence the resting membrane potential?
Ion concentrations inside and outside the cell, permeability of the membrane to different ions, and the activity of ion pumps.
What role do ion channels play in maintaining RMP?
They allow selective permeability to ions, influencing the membrane potential.
What is the typical resting membrane potential of a neuron?
Approximately -70 mV.
