69 Questions
What is the fundamental driving force behind the movement of ions across a neuronal membrane?
Nernst potentials and electrochemical gradients
During an action potential, what is the primary mechanism that allows for rapid and self-propagating changes in membrane potential?
Voltage-gated ion channels opening and closing
What is the primary mechanism by which neurotransmitters are released from the presynaptic terminal?
Exocytosis of synaptic vesicles containing neurotransmitters
What is the primary mechanism by which postsynaptic potentials (EPSPs and IPSPs) are generated?
Binding of neurotransmitters to ionotropic receptors
What is the primary difference between action potentials and graded potentials (EPSPs and IPSPs) in terms of their electrophysiological properties?
Action potentials are self-propagating, while graded potentials are not
What is the main purpose of the action potential in the presynaptic terminal?
To increase the intracellular calcium concentration
Which protein complex is responsible for 'docking' the neurotransmitter-filled vesicles to the presynaptic membrane?
v-SNAREs and t-SNAREs
What is the role of Complexin in the process of neurotransmitter release?
It binds to the v-SNARE-t-SNARE complex to prevent premature release
What is the main source of calcium that triggers neurotransmitter release in the presynaptic terminal?
Calcium influx through voltage-gated calcium channels
What is the role of Synaptotagmin in the process of neurotransmitter release?
It acts as a calcium sensor to trigger vesicle fusion
What is the time scale of the process of neurotransmitter release following the arrival of the action potential?
Milliseconds
What is the primary function of the inactivation gate in voltage-gated sodium channels?
To prevent continuous influx of sodium ions after the initial depolarization
Which of the following conditions must be met for the inactivation gate to reopen?
A minimum of 1-2 milliseconds must have passed since the inactivation gate closed
During the absolute refractory period, which of the following statements is true?
The inactivation gate of the sodium voltage-gated channel is closed
What is the primary characteristic of the relative refractory period?
The membrane potential is lower than the resting membrane potential
Which of the following statements about action potentials is true?
Action potentials are all-or-none events with constant amplitude and conduction velocity
What is the primary role of potassium voltage-gated channels in the action potential?
To facilitate the repolarization of the membrane potential
What is the main factor that determines the rate of flow of charges across a cell membrane?
The permeability of the membrane to the charged particles
What is the Nernst potential?
The membrane potential at which the inward and outward movement of an ion through a channel is balanced and equal
Why is the resting membrane potential of a neuron typically close to, but not the same as, the Nernst potential for potassium?
All of the above
What is the main factor that determines the equilibrium potential for a specific ion?
The relative concentrations of the ion on the two sides of the membrane
Which of the following statements about Ohm's law is correct?
Ohm's law describes the relationship between current, voltage, and resistance in an electrical circuit
How does the permeability of the cell membrane to different ions affect the resting membrane potential?
The resting membrane potential is determined by the relative permeabilities to all ions, not just potassium
What is the relationship between the Nernst potential and the resting membrane potential in a neuron?
The resting membrane potential is typically close to, but not the same as, the Nernst potential for potassium
What is the main factor that determines the direction of ion movement across a cell membrane?
Both the concentration gradient and the electrical potential difference
How does the Nernst potential equation relate to the resting membrane potential of a neuron?
The Nernst potential equation describes the equilibrium potential for a single ion, which is different from the resting membrane potential
Which of the following accurately describes an inhibitory receptor's effect on the dendrite membrane potential?
It causes hyperpolarization (membrane becomes more negative)
Which statement accurately describes the properties of graded potentials?
They decrease in magnitude over time and distance traveled, can vary in size, and can summate
If multiple excitatory postsynaptic potentials (EPSPs) from different sites meet at the same location on the membrane at the same time, what phenomenon occurs?
Spatial summation
What is the primary advantage of chemical synapses and graded potentials over relying solely on action potentials for neuronal communication?
They enable a wide array of signal integration and complexity
If an excitatory postsynaptic potential (EPSP) reaches the axon hillock and exceeds the threshold for action potential generation, but no voltage-gated sodium channels are present, what will happen?
No action potential will be generated
Which of the following statements accurately describes the role of metabotropic receptors in neuronal signaling?
They can have long-lasting effects that include protein synthesis and intracellular signals
If multiple excitatory postsynaptic potentials (EPSPs) occur in a "staircase" fashion over time and summate, what phenomenon is occurring?
Temporal summation
What is the primary function of the axon hillock in neuronal signaling?
To summate excitatory and inhibitory postsynaptic potentials
Which of the following statements accurately describes the relationship between graded potentials and action potentials?
Graded potentials are necessary for the generation of action potentials
Which of the following accurately describes the complexity of neuronal computation?
Neurons are complex computational devices that integrate a wide array of inputs
What is the primary mechanism responsible for the rapid and self-propagating changes in membrane potential during an action potential?
The sequential opening and closing of voltage-gated sodium and potassium channels
What is the primary function of the axon hillock in neuronal signaling?
To integrate and summate incoming postsynaptic potentials
Which of the following statements accurately describes the complexity of neuronal computation?
Neuronal computation involves complex nonlinear integration of inputs from multiple sources
What is the primary advantage of chemical synapses and graded potentials over relying solely on action potentials for neuronal communication?
They allow for more complex computations and integration of inputs
What is the primary mechanism by which neurotransmitters are released from the presynaptic terminal?
Exocytosis of synaptic vesicles containing neurotransmitters
What determines the membrane potential when the membrane is permeable to more than one ion?
Goldman Field equation
Which type of channels can open or close in response to a variety of stimuli?
Voltage-gated channels
What occurs in the axon hillock that allows for the production of action potentials?
Positive feedback mechanism
What happens during an action potential regarding the membrane voltage change?
It changes rapidly
Which population of channels is crucial for the generation of action potentials?
Calcium voltage-gated channels
What type of receptors are ionotropic receptors, according to the text?
Ligand-gated receptors
Which of the following statements accurately describes the role of the inactivation gate in voltage-gated sodium channels?
It prevents further sodium influx once the membrane has depolarized, allowing for repolarization to occur.
During the relative refractory period, what is the primary reason for the increased stimulus required to reach the threshold for action potential generation?
The inactivation gate of the sodium channels is open, but the activation gate is closed, necessitating a larger stimulus.
What is the primary reason for the constant amplitude of action potentials, regardless of the strength of the stimulus?
Once the threshold is reached, all available sodium channels open, resulting in a maximal depolarization.
Which of the following statements accurately describes the relationship between the resting membrane potential and the Nernst potential for potassium ions?
The resting membrane potential is typically less negative than the Nernst potential for potassium ions.
What is the primary mechanism that allows for the rapid and self-propagating changes in membrane potential during an action potential?
The opening and closing of voltage-gated sodium and potassium channels, respectively.
Which of the following statements accurately describes the role of the potassium voltage-gated channels in the action potential?
They open after the sodium channels have inactivated, allowing potassium efflux and repolarization of the membrane.
What is the primary reason why myelination of axons increases the speed of action potential propagation?
Myelin insulates the axon, allowing the action potential to 'jump' between nodes of Ranvier through saltatory conduction.
Which of the following is the primary reason why the speed of action potential propagation increases with larger axon diameter?
Larger axons have a lower membrane resistance, allowing for faster depolarization.
In the context of saltatory conduction, what is the primary role of the nodes of Ranvier?
The nodes of Ranvier are the only regions of the axon where voltage-gated ion channels are expressed.
Which of the following is the primary advantage of chemical synapses over electrical synapses in neuronal communication?
Chemical synapses allow for more complex and fine-tuned modulation of neuronal activity.
What is the primary role of the synaptic cleft in the process of neurotransmitter release and action at a chemical synapse?
The synaptic cleft is the space across which the released neurotransmitters must diffuse to reach and bind to the postsynaptic receptors.
Which of the following is the primary mechanism by which the resting membrane potential of a neuron is maintained?
The selective permeability of the cell membrane to different ions, particularly potassium, as described by the Nernst equation.
What is the primary role of the inactivation gate in voltage-gated sodium channels during an action potential?
The inactivation gate helps to rapidly close the sodium channels after the initial depolarization, preventing continuous sodium influx.
Which of the following is the primary mechanism by which neurotransmitters are released from the presynaptic terminal?
Neurotransmitters are released from the presynaptic terminal through exocytosis, where synaptic vesicles fuse with the presynaptic membrane.
What is the primary advantage of saltatory conduction in myelinated axons compared to continuous conduction in non-myelinated axons?
Saltatory conduction allows for faster propagation of action potentials along the axon.
What is the primary mechanism by which Botox impairs the release of neurotransmitters at the presynaptic terminal?
Botox binds to and inactivates SNAP-25, a v-SNARE protein, preventing the fusion of synaptic vesicles with the presynaptic membrane.
Which of the following statements accurately describes the role of complexin in the process of neurotransmitter release at the presynaptic terminal?
Complexin binds to the SNARE complex and prevents premature fusion of the synaptic vesicle with the presynaptic membrane until calcium influx triggers its disengagement.
What is the primary mechanism by which neurotransmitters are removed from the synaptic cleft after their release?
Neurotransmitters are degraded by enzymes in the synaptic cleft, such as acetylcholinesterase for acetylcholine.
How do the effects of different neurotransmitters vary at the postsynaptic cell?
Different neurons release different neurotransmitters, and different postsynaptic cells express different receptors for those neurotransmitters, leading to diverse effects.
What is the primary mechanism by which metabotropic neurotransmitter receptors influence postsynaptic cell function?
Metabotropic receptors activate G-protein signaling cascades that can modulate the activity of enzymes and transcription factors, leading to longer-term changes in cell function.
Which of the following statements accurately describes the role of synaptotagmin in the process of neurotransmitter release at the presynaptic terminal?
Synaptotagmin works in conjunction with complexin to prevent premature fusion of synaptic vesicles until the arrival of an action potential.
How do the effects of neurotransmitters on the postsynaptic cell membrane potential differ between ionotropic and metabotropic receptors?
Ionotropic receptors cause rapid, transient changes in membrane potential by directly opening ion channels, while metabotropic receptors cause slower, longer-lasting changes through G-protein signaling cascades.
Study Notes
Electrochemical Events of the Axon
- The movement of a dissolved, charged particle (ion) across a lipid membrane depends on:
- The charge of the particle
- The difference in distribution of charges across the membrane (voltage)
- The permeability of the membrane to the charged particle
- Ohm's law: I = V/R, where I = current, V = voltage, and R = resistance
- In biology, Ohm's law is most useful when thinking about unequal distributions of charges very close on either side of a membrane
Nernst Potentials
- The Nernst potential is the membrane potential at which the inward and outward movement of an ion through a channel is balanced and equal
- It is a balance between the diffusional force (movement of an ion down its concentration gradient) and the electrical force (attraction or repulsion based on the charge of the ion and the charge across the membrane)
- The Nernst potential describes the energy gradient and does not include the flow of ions (current) or the resistance of the membrane to flow
Resting Membrane Potential
- The resting membrane potential of a neuron is typically close to the Nernst potential for K+ (around -75mV)
- This is due to the high permeability of the neuronal membrane to K+ at rest
Action Potentials
- Properties of action potentials:
- All-or-none events
- Initiated by depolarization
- Have constant amplitude
- Have constant conduction velocity along a fiber
- The action potential is a rapid depolarization of the membrane, resulting in a positive change in membrane voltage
- The sequence of events in an action potential:
- Depolarization to -55mV
- Sodium channels open, allowing Na+ to rush into the cell
- The inactivation gate of the sodium channel closes, preventing further sodium influx
- Potassium channels open, allowing K+ to leave the cell and repolarize the membrane
- The inactivation gate of the sodium channel opens again, and the cycle repeats
Refractory Periods
- Absolute refractory period: The period during which the inactivation gate of the sodium channel is closed, and another action potential is impossible
- Relative refractory period: The period during which the inactivation gate is open, but the activation gate is closed, and the cell is hyperpolarized
Synaptic Transmission
- The sequence of events in synaptic transmission:
- The action potential arrives at the presynaptic terminal
- Depolarization leads to the opening of voltage-gated calcium channels
- Calcium enters the presynaptic terminal
- Calcium binds to a protein associated with neurotransmitter-filled vesicles
- Neurotransmitter is released into the synapse
- Neurotransmitter binds to a receptor on the postsynaptic cell
Graded Potentials
- Properties of graded potentials:
- They are changes in membrane potential that do not result in an action potential
- They are decremental, meaning they decrease in size over time and distance
- They can vary in magnitude
- They can summate, or add together
- They can be excitatory (depolarization) or inhibitory (hyperpolarization)
Integration of Electrical Events
-
The integration of electrical events at the level of the neuron involves the summation of graded potentials from multiple synapses
-
The net result of these graded potentials can bring the axon hillock to threshold, resulting in an action potential### Conduction Velocity of Nerve Fibers
-
Myelinated fiber velocity (m/s) = diameter (um) x 4.5
-
Unmyelinated fiber velocity (m/s) = square root of diameter (um)
-
Increase in conduction velocity with increased size of the axon diameter is true for both myelinated and unmyelinated axons
Continuous Conduction
- Action potential progresses continuously along the length of the axon, reproduced by depolarization of neighboring parts of the axon
- This process is slower due to the need for each part of the axon to depolarize and reach threshold
Saltatory Conduction
- In myelinated axons, nodes of Ranvier are the only parts expressing voltage-gated channels
- Myelin insulation allows the electrical field to "jump" to the next node of Ranvier, making it a faster process
- The positive electric field from one node of Ranvier brings the next node up to threshold
Types of Nerve Fibers
- A Fibers: largest fibers (5-20 μm), myelinated, conduct impulses at 12-130 m/sec (280 miles/hr), associated with touch, pressure, position, heat, and cold
- B Fibers: medium fibers (2-3 μm), non-myelinated, conduct impulses at 15 m/sec (32 miles/hr), from viscera to brain and spinal cord, autonomic efferents to autonomic ganglia
- C Fibers: smallest fibers, non-myelinated, conduct impulses at 0.5-2 m/sec (1-4 miles/hr), associated with pain, touch, pressure, heat, cold, and visceral efferents
Chemical Synapses
- Chemical synapses are associated with excitable cells
- Presynaptic neuron releases a neurotransmitter that binds to receptors embedded in the post-synaptic cell membrane
- Neurotransmitter crossing the synaptic cleft can affect the postsynaptic cell in various ways
- Synapse is usually between a dendritic spine or an axon terminal, with the dendritic spine expressing the receptor for the neurotransmitter
Neurotransmitter Vesicles
- Vesicles are synthesized and packaged in the rER and Golgi and transported down the axon via microtubules
- Neurotransmitters (non-peptide) are synthesized in the cytosol of the presynaptic terminal and transported into vesicles
- Vesicles bind to the actin within the presynaptic terminal cytoskeleton and are transported to release sites close to the synapse
Explore the electrical events of the axon, including resting membrane potential, action potentials, voltage-gated channels, refractory periods, synaptic transmission, and more in this overview of Week 11 in Dr. Vargo's BMS 100 course.
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