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Questions and Answers
What is the primary mechanism through which excitation occurs in postsynaptic cells?
What is the primary mechanism through which excitation occurs in postsynaptic cells?
- Decrease of calcium conductance
- Opening of chloride channels
- Increase of potassium conductance out of the neuron
- Opening of sodium channels (correct)
Which mechanism leads to inhibition in a postsynaptic neuron?
Which mechanism leads to inhibition in a postsynaptic neuron?
- Opening of chloride channels (correct)
- Opening of sodium channels
- Decrease in potassium efflux
- Increase in calcium influx
Which substance is usually classified as excitatory?
Which substance is usually classified as excitatory?
- Glycine
- Dopamine
- Glutamate (correct)
- GABA
What effect does increasing the resting membrane potential have on neuronal excitability?
What effect does increasing the resting membrane potential have on neuronal excitability?
How does the conduction through potassium channels affect excitation?
How does the conduction through potassium channels affect excitation?
What is the role of receptor enzymes in neuronal inhibition?
What is the role of receptor enzymes in neuronal inhibition?
Which of the following changes increases the likelihood of excitation?
Which of the following changes increases the likelihood of excitation?
What defines the resting membrane potential in neurons?
What defines the resting membrane potential in neurons?
What triggers the release of neurotransmitters from presynaptic terminals?
What triggers the release of neurotransmitters from presynaptic terminals?
What is the role of inhibitory receptors in the postsynaptic membrane?
What is the role of inhibitory receptors in the postsynaptic membrane?
How do excitatory postsynaptic potentials (EPSPs) differ from inhibitory postsynaptic potentials (IPSPs)?
How do excitatory postsynaptic potentials (EPSPs) differ from inhibitory postsynaptic potentials (IPSPs)?
What is the primary ion involved in the triggering of neurotransmitter release at presynaptic terminals?
What is the primary ion involved in the triggering of neurotransmitter release at presynaptic terminals?
Which explanation correctly describes the role of the axon hillock?
Which explanation correctly describes the role of the axon hillock?
What does spatial summation refer to?
What does spatial summation refer to?
Which state of a neuron corresponds to when it is less likely to generate an action potential?
Which state of a neuron corresponds to when it is less likely to generate an action potential?
What best defines an excitatory postsynaptic potential (EPSP)?
What best defines an excitatory postsynaptic potential (EPSP)?
What is the normal intraneuronal potential of a resting neuron?
What is the normal intraneuronal potential of a resting neuron?
Which ions are primarily involved in the different states of neuronal function?
Which ions are primarily involved in the different states of neuronal function?
What causes a neuron to enter an excited state?
What causes a neuron to enter an excited state?
What is the minimal change in voltage that signifies an excitatory postsynaptic potential (EPSP)?
What is the minimal change in voltage that signifies an excitatory postsynaptic potential (EPSP)?
What process is required for a single presynaptic terminal to significantly increase neuronal potential?
What process is required for a single presynaptic terminal to significantly increase neuronal potential?
How does a neurotransmitter work when secreted into the synaptic cleft?
How does a neurotransmitter work when secreted into the synaptic cleft?
Which potential must an EPSP reach to elicit an action potential in the postsynaptic neuron?
Which potential must an EPSP reach to elicit an action potential in the postsynaptic neuron?
What does temporal summation involve?
What does temporal summation involve?
What role do chloride ions play in synaptic transmission?
What role do chloride ions play in synaptic transmission?
What happens to a neuron when it is facilitated?
What happens to a neuron when it is facilitated?
What is the primary reason a single presynaptic terminal usually fails to excite a neuron?
What is the primary reason a single presynaptic terminal usually fails to excite a neuron?
Which statement correctly describes an excitatory post-synaptic potential (EPSP)?
Which statement correctly describes an excitatory post-synaptic potential (EPSP)?
What is 'spatial summation' in the context of neuronal firing?
What is 'spatial summation' in the context of neuronal firing?
What causes excitation in neurons?
What causes excitation in neurons?
What occurs during 'temporal summation'?
What occurs during 'temporal summation'?
Which type of synapse is most commonly found in the nervous system?
Which type of synapse is most commonly found in the nervous system?
What effect does an IPSP have on the postsynaptic membrane potential?
What effect does an IPSP have on the postsynaptic membrane potential?
What can happen if an EPSP and an IPSP occur simultaneously?
What can happen if an EPSP and an IPSP occur simultaneously?
What occurs when potassium channels open in a neuron?
What occurs when potassium channels open in a neuron?
What triggers an action potential in the context of multiple synaptic inputs?
What triggers an action potential in the context of multiple synaptic inputs?
Why is the stimulation of motor and sensory neurons during reflexes significant?
Why is the stimulation of motor and sensory neurons during reflexes significant?
What role do ligand-gated sodium channels play in synaptic transmission?
What role do ligand-gated sodium channels play in synaptic transmission?
In which scenario is presynaptic inhibition likely to occur?
In which scenario is presynaptic inhibition likely to occur?
What must occur for the exocytosis of neurotransmitters to take place?
What must occur for the exocytosis of neurotransmitters to take place?
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Study Notes
Mechanism of Neurotransmitter Release
- An action potential causes depolarization of the presynaptic membrane, opening voltage-gated calcium channels.
- Calcium ions influx into the presynaptic terminal directly influences neurotransmitter release into the synaptic cleft.
Excitation of the Postsynaptic Membrane
- Activated excitatory receptors lead to:
- Opening of sodium channels, allowing positive charges to flow into the postsynaptic neuron, raising membrane potential.
- Reduced conductance through potassium and chloride channels, increasing positivity inside the neuron.
- Alterations in internal metabolism that may enhance excitatory receptors or limit inhibitory ones.
Inhibition of the Postsynaptic Membrane
- Inhibitory mechanisms include:
- Opening of chloride channels allows negative chloride ions to enter, increasing negativity within the neuron.
- Increased efflux of potassium ions, which also leads to a more negative internal potential.
- Activation of enzymes that decrease the number of excitatory receptors or increase inhibitory receptors.
Common Neurotransmitters
- Acetylcholine: predominantly excitatory.
- Norepinephrine: typically excitatory.
- Dopamine: functions as an inhibitor.
- Glycine and GABA: key inhibitory neurotransmitters.
- Glutamate: primarily excitatory.
- Serotonin: inhibitory role in pain modulation.
Neuronal States and Membrane Potentials
- Neuron states include:
- Resting state: approximately -65 mV.
- Excited state: around -45 mV (due to sodium influx).
- Inhibited state: about -70 mV (following potassium efflux or chloride influx).
- Changes in membrane potential correlate with ion movement: sodium influx depolarizes, while potassium and chloride movements can hyperpolarize.
Definitions and Comparisons
- EPSP (Excitatory Postsynaptic Potential): Depolarization that moves potential towards threshold for action potential.
- IPSP (Inhibitory Postsynaptic Potential): Hyperpolarization that moves potential away from threshold.
- EPSPs differ from action potentials as they are graded and not all-or-none responses.
- Spatial summation: Multiple terminals activate simultaneously, leading to EPSP accumulation.
- Temporal summation: Rapid successive firings from a single terminal that build upon prior potentials.
Generation of Action Potentials
- Action potentials are generated when the summed EPSPs reach the threshold at the axon hillock.
- The axon hillock integrates all inputs and is crucial for determining neuronal firing.
Membrane Excitability
- High threshold membranes require greater stimulation to become excited compared to low threshold membranes.
- Facilitated neurons are closer to action potential threshold and respond more easily to additional excitatory inputs.
Interactive Mechanisms
- Simultaneous inputs of EPSPs and IPSPs can cancel out the effects, preventing action potential generation.
- Neuronal facilitation allows a neuron to be primed for easier excitation upon subsequent stimulation, enhancing responsiveness to new signals.
Learning Scenario Insight
- The ease of manipulating fine beads without gloves emphasizes the significance of tactile feedback and sensation in motor control, paralleling neurophysiological processes involving synaptic transmission and receptor activation.
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