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Questions and Answers
What role does temporal summation play in neuron communication?
How do action potentials maintain uniformity despite varying stimuli strengths?
What effect does long-term potentiation (LTP) have on synaptic connections?
What is the consequence of desensitization during high-frequency action potential firing?
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Which of the following best describes a convergent pathway?
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What might happen to signal propagation if a neurotransmitter is blocked by a neurotoxin?
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What does neuronal plasticity allow the nervous system to do?
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What factors are primarily involved in determining the strength of a stimulus?
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What is the significance of myelination in nerve impulse propagation?
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What effect does multiple sclerosis have on action potentials?
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During saltatory conduction, where are action potentials primarily generated?
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What is the role of the axon hillock in a neuron?
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How do graded potentials differ from action potentials?
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What happens during the refractory period of a neuron?
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What role do neurotransmitters play in chemical synapses?
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What general effect do neurotoxins have on neural function?
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In what direction does synaptic transmission typically operate?
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What do dendritic spines primarily facilitate?
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What is the main function of myelination in neurons?
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What occurs during the absolute refractory period?
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What characterizes the propagation of action potential in myelinated fibers?
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What is the effect of tetrodotoxin on neurons?
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What is a key difference between graded potentials and action potentials?
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How does repolarization occur during an action potential?
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What is the role of Na+-K+ pumps in neurons?
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What distinguishes the refractory periods?
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During which phase of action potential does the membrane potential become more positive?
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What happens to the action potential as it travels down a non-myelinated axon?
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Which of the following best describes graded potentials?
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What is the outcome of the opening of chemically gated ion channels in a neuron?
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Myelinated axons are more efficient due to which of the following characteristics?
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What defines the duration of the refractory period in neurons?
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Study Notes
Membrane Potential
- The voltage difference across a cell membrane is called membrane potential.
- The resting membrane potential of a neuron cell is approximately -70 mV
- The intracellular fluid has a slight excess of anions and the extracellular fluid has a slight excess of cations.
- The Na+-K+ pump maintains the resting membrane potential at the expense of energy.
- The Na+-K+ pump also functions as a leaky channel, letting potassium ions pass through the membrane.
Change of Membrane Potential
- Nerve and muscle tissues are excitable tissues, because their membrane potential can be altered.
- The change of membrane potential is categorized as polarization, depolarization, repolarization, and hyperpolarization.
- Ion movement can only be mediated by channels.
Ion Channels
- Pores that open and close provide a passageway for ions to pass through a membrane.
- There are leaky channels and gated channels.
- Gated channels can be voltage-gated, chemically gated, mechanically gated, or thermally gated.
Generation of Electrical Signals in Neuron
- Neurons generate an electrical signal via changes in membrane potential.
- Such changes in membrane potential are brought about by changes in ion movement.
- Two basic types of electrical signals are graded potential and action potential.
Graded Potential
- It is the depolarization of membrane in a small and specialized region of the total membrane.
- It is initiated by Na+ entry into the cell and the ions flow from the active site to the inactive site, causing a current along the membrane.
- It is bi-directional over a short distance.
- It functions as a short-distance signal.
- Graded potential is a localized change in the membrane potential that is graded depending on the intensity of the stimulus.
Action Potential
- It is a brief, rapid, large change in membrane potential.
- It is initiated when the membrane potentials reach threshold potential.
- It is generated at the axon hillock and propagated throughout the entire membrane, nondecrementally.
- It serves as a long-distance signal.
- It has a fixed threshold and magnitude and is all-or-none.
Conformations of voltage-gated Na+ and K+ channels
- Channels can open or close when they are in different conformations.
- The channels are responsible for the formation of action potential and are voltage-gated, meaning they are opened and closed by changes in membrane potential.
Formation of Action Potential
- Rapid fluxes of Na+ and K+ cause the action potential.
- Opening and closing of voltage-gated Na+ channels and voltage-gated K+ channels lead to the action potential.
- Graded potential activates the opening of Na+ channels (fast).
- Slow closure of Na+ channel and the opening of K+ channels (slow).
- The positive feedback of Na+ channel allows for rapid depolarization.
Refractory Period
- After the action potential, there is a time period when new action potential cannot be initiated.
- Divided into the absolute refractory period and the relative refractory period.
Myelination
- Axons covered with myelin along the length are called myelinated fibers.
- Myelin is a thick layer produced by oligodendrocytes in the CNS and Schwann cells in the PNS.
- Myelin serves as an insulator and prevents leakage of current, allowing for faster transmission of action potential.
- Nodes of Ranvier are unmyelinated gaps between myelinated segments.
Saltatory Conduction
- Myelinated axons conduct action potential faster than unmyelinated axons due to saltatory conduction.
- Action potential is only produced at the nodes of Ranvier, where Na+ channels are concentrated.
- The current moves under the myelin sheath but diminishes in amplitude.
- Na+ entry at the node reinforces the depolarization and keeps the magnitude high enough for the next action potential.
Propagation of nerve impulse
- Once an action potential is initiated, no further triggering event is needed to activate the remaining segment of the fiber.
- Conducted through contiguous conduction or saltatory conduction.
- Contiguous conduction occurs in non-myelinated axons and the action potential spreads along every patch of membrane down the axon.
- Once the original action potential is initiated it starts a self-perpetuating cycle where new action potentials are formed and propagated along the fiber.
Graded potential vs action potential
- Graded potential is a localized change in membrane potential that is graded depending on the intensity of the stimulus, whereas action potential is an all-or-none event.
- Action potentials are triggered when the membrane potential reaches the threshold.
- Graded potential only occurs in a small region of the membrane, whereas action potential is propagated along the entire membrane.
Neurotoxins
- Tetrodotoxin (TTX) is found in the pufferfish and blocks voltage-gated Na+ channels, thus preventing action potential generation.
- TTX is extremely deadly and can cause paralysis, loss of consciousness, respiratory failure, and death.
Multiple sclerosis
- An autoimmune disease, multiple sclerosis, attacks the nervous system, destroying myelin sheath.
- This slows the transmission of nerve impulse and may block the propagation of action potentials.
- Symptoms may depend on the affected axons and there is currently no cure.
Integration of information transfer between neurons
- Information is transferred between neurons via synapses, either electrical or chemical.
- It is a unidirectional process.
Chemical Synapse
- A specialized junction where information is transferred from one neuron to another.
- Synaptic vesicles containing neurotransmitters are released at the axon terminal.
- The neurotransmitters diffuse across the synaptic cleft and bind to receptors on the postsynaptic neuron.
- The neurotransmitter binding initiates a new action potential on the postsynaptic neuron.
Determination of the Post-synaptic Potential
- The combination of excitatory postsynaptic potential (EPSP) and inhibitory postsynaptic potential (IPSP) determines the postsynaptic potential.
- Temporal summation is when several EPSP occur close together in time.
- Spatial summation is when EPSP originate simultaneously from several presynaptic inputs.
- Temporal and spatial summation can lead to action potential on the postsynaptic neuron.
Memory
- Memory is the storage of acquired knowledge for later recall.
- Short-term memory lasts seconds to hours.
- Long-term memory lasts days to years and involves the process of consolidation, transferring short-term memory into long-term memory.
- There is not a single memory center in the brain, but many brain regions are involved, such as the cerebellum, prefrontal cortex, and hippocampus.
- The brain involves both structural and functional changes during the consolidation process.
Long-term potentiation
- LTP is a form of synaptic plasticity that occurs when repetitive stimulation of a particular synapse leads to an increase in the strength of synaptic connection.
- This happens when synaptic transmission is strengthened over time due to repetitive use.
- This is attributed to a strengthening of synapses in the brain due to a long-term increase in the efficiency of signal transmission across synapses.
- It is important to note that this process is not fully understood and research is ongoing to understand it better.
What determines the strength of a stimulus?
- The frequency of action potentials, the amount of neurotransmitter released, and the duration of release determine the strength of a stimulus.
- The frequency of action potentials can determine the amount of neurotransmitter release.
- Neurotransmitter release can decrease at high frequencies, leading to desensitization, a reduction in response to a stimulus.
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Description
Explore the concepts of membrane potential, including resting and changing states. Understand the roles of ion channels and the Na+-K+ pump in neuronal function and excitability. Test your knowledge about polarization, depolarization, and related mechanisms in nerve and muscle tissues.
