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Questions and Answers
What is the primary function of inhibitory post-synaptic potentials (IPSPs) in neuronal signaling?
What is the primary function of inhibitory post-synaptic potentials (IPSPs) in neuronal signaling?
Where are IPSPs typically located in relation to excitatory post-synaptic potentials (EPSPs)?
Where are IPSPs typically located in relation to excitatory post-synaptic potentials (EPSPs)?
How do IPSPs affect the membrane potential when depolarization occurs?
How do IPSPs affect the membrane potential when depolarization occurs?
What ions are predominantly involved in generating an IPSP?
What ions are predominantly involved in generating an IPSP?
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What happens when summated EPSPs reach the trigger zone of a neuron?
What happens when summated EPSPs reach the trigger zone of a neuron?
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Which of the following best describes temporal summation?
Which of the following best describes temporal summation?
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Which characteristic distinguishes IPSPs from EPSPs in neuronal signaling?
Which characteristic distinguishes IPSPs from EPSPs in neuronal signaling?
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Why are IPSPs considered strategically advantageous in neuronal circuitry?
Why are IPSPs considered strategically advantageous in neuronal circuitry?
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What primarily determines the effect of neurotransmitter binding to a receptor?
What primarily determines the effect of neurotransmitter binding to a receptor?
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Which type of receptor directly opens ion channels upon ligand binding?
Which type of receptor directly opens ion channels upon ligand binding?
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What occurs during spatial summation at synapses?
What occurs during spatial summation at synapses?
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The main role of second messengers in metabotropic receptor activity is to:
The main role of second messengers in metabotropic receptor activity is to:
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Which of the following ions is associated with the generation of an excitatory postsynaptic potential (EPSP)?
Which of the following ions is associated with the generation of an excitatory postsynaptic potential (EPSP)?
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What is the expected duration of a postsynaptic potential (PSP) when neurotransmitters are present?
What is the expected duration of a postsynaptic potential (PSP) when neurotransmitters are present?
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Which neurotransmitter is primarily associated with ionotropic receptors in the synapse?
Which neurotransmitter is primarily associated with ionotropic receptors in the synapse?
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What happens to postsynaptic potentials summation when multiple rapid signals arrive at a synapse from the same location?
What happens to postsynaptic potentials summation when multiple rapid signals arrive at a synapse from the same location?
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What initiates the production of second messengers like cAMP in response to noradrenalin binding to the β-adrenoreceptor?
What initiates the production of second messengers like cAMP in response to noradrenalin binding to the β-adrenoreceptor?
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What is the primary reason that postsynaptic potentials (PSPs) cannot initiate an action potential in neuronal dendrites?
What is the primary reason that postsynaptic potentials (PSPs) cannot initiate an action potential in neuronal dendrites?
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Which enzyme is primarily activated through the G-protein coupled pathway during metabotropic receptor activation?
Which enzyme is primarily activated through the G-protein coupled pathway during metabotropic receptor activation?
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What characterizes temporal summation in postsynaptic potentials (PSPs)?
What characterizes temporal summation in postsynaptic potentials (PSPs)?
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What physiological effect results from the phosphorylation of calcium channels following β-adrenoreceptor activation?
What physiological effect results from the phosphorylation of calcium channels following β-adrenoreceptor activation?
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What are the two types of PSP summations that occur in neurons?
What are the two types of PSP summations that occur in neurons?
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What is typically required for an action potential to be generated at the trigger zone of a neuron?
What is typically required for an action potential to be generated at the trigger zone of a neuron?
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What type of receptor is the muscarinic receptor associated with, during ligand binding?
What type of receptor is the muscarinic receptor associated with, during ligand binding?
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How does the property of poor cable conduction in biological tissues affect PSPs?
How does the property of poor cable conduction in biological tissues affect PSPs?
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Which of the following is NOT typically a second messenger activated during metabotropic receptor signaling?
Which of the following is NOT typically a second messenger activated during metabotropic receptor signaling?
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Study Notes
Post-Synaptic Receptors
- Two main types: ionotropic and metabotropic.
- Ionotropic receptors directly open ion channels upon ligand binding, leading to rapid changes in membrane potential.
- Metabotropic receptors initiate metabolic cascades, often involving G-protein-coupled enzymes and second messengers (cAMP, cGMP, IP3), resulting in slower, more prolonged effects on ion channels and other cellular processes.
Ionotropic Effects
- Ligand binding directly opens ion channels.
- Results in a post-synaptic potential (PSP) lasting 20-40ms.
- Cation-specific channels (Na+, K+) cause excitatory post-synaptic potentials (EPSPs) – depolarization.
- Anion-specific channels (Cl-) or K+ channels cause inhibitory post-synaptic potentials (IPSPs) – hyperpolarization.
- Examples of ionotropic receptor ligands include acetylcholine, glutamate, GABA, and glycine. The receptor type, not the ligand, determines the effect.
- Nicotinic acetylcholine receptors are an example of an ionotropic receptor.
Metabotropic Effects
- Ligand binding activates a G-protein-coupled enzyme.
- Enzyme activation leads to increased or decreased production of second messengers.
- Second messengers activate enzymes, often kinases, which phosphorylate membrane proteins (like ion channels), modulating ion currents.
- Effects are slower than ionotropic effects because of the intermediary enzyme steps. Membrane potential changes may be slow or absent, although ion current changes may occur.
- Examples of metabotropic receptor ligands include acetylcholine (muscarinic receptors), various peptides (substance P, β-endorphin, ADH), catecholamines (noradrenaline, dopamine), serotonin, purines (adenosine, ATP), and gases (NO, CO).
β-Adrenoreceptor
- A metabotropic receptor for noradrenaline.
- Noradrenaline binding activates adenylyl cyclase via G-protein, increasing cAMP production.
- cAMP activates kinases that phosphorylate calcium channels, increasing calcium influx. This is important in heart muscle, increasing contractility.
- Beta-blockers are relevant to this receptor system.
Spread of PSPs
- PSPs are generated in inexcitable neuronal dendrites and cell bodies (lacking high density of voltage-gated Na+ channels).
- They cannot initiate action potentials (APs).
- They spread passively to the axon's initial segment (trigger zone).
- Passive conduction leads to current loss before reaching the trigger zone.
PSP Summations
- Biological tissues have poor cable properties.
- Current loss occurs during passive conduction, impacting signal strength at the trigger zone.
- Two types: spatial and temporal summation.
Types of PSP Summation
- Spatial summation involves multiple PSPs from different synapses arriving simultaneously.
- Temporal summation involves multiple PSPs from the same synapse arriving in quick succession.
Inhibitory Post-Synaptic Potential (IPSP)
- Often located on the cell soma, strategically positioned to shunt EPSP currents away from the trigger zone.
- Typically involve the opening of Cl- channels.
- At resting potential, opening Cl- channels produces little change.
- During depolarization, opening of Cl- channels brings the membrane potential back towards the resting potential, counteracting excitation.
- In the nervous system, IPSPs are often more influential than EPSPs.
Generating a Spike Train
- Summated EPSPs reaching the trigger zone cause it to reach threshold and initiate an action potential.
- Prolonged strong synaptic input might result in a sustained depolarizaton causing bursts of repeated action potentials (spike trains) for hundreds of milliseconds.
Transmitter Removal
- The text does not explicitly detail mechanisms of neurotransmitter removal from the synapse.
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Description
Explore the two main types of post-synaptic receptors: ionotropic and metabotropic. Learn how ionotropic receptors function by directly opening ion channels and causing rapid changes in membrane potential. Delve into the effects of various ligands and the significance of receptor types in neuronal signaling.
