L6: Synaptic Signalling Flashcards
What is the primary focus of the lecture on synaptic signaling?
Neurone-to-neurone communication, focusing on how one neurone talks to another and synaptic integration.
What is a synapse?
The gap between a presynaptic neurone and a postsynaptic neurone where neurotransmitters are released and interact with receptors.
What are the two main types of synaptic signaling mechanisms?
Isotropic (ligand-gated ion channels) and metabotropic (G-protein coupled receptors).
What determines the excitability of the postsynaptic neurone?
The balance of excitatory (e.g., sodium influx) and inhibitory (e.g., chloride influx) synaptic inputs.
What is spatial summation in synaptic integration?
The additive effect of excitatory postsynaptic potentials (EPSPs) from multiple synapses occurring simultaneously.
What is temporal summation in synaptic integration?
The additive effect of EPSPs from the same synapse occurring in rapid succession.
Why is the axon hillock an influential site in synaptic signaling?
Synaptic inputs closer to the axon hillock have a greater influence on action potential generation.
What happens during the refractory period after an action potential?
Voltage-gated sodium channels enter an inactive state, preventing immediate firing of another action potential.
How is stimulus strength encoded in neurones?
By the frequency of action potentials, not their amplitude.
What is excitotoxicity and what condition is it linked to?
Excessive neuronal excitation leading to cell death, often associated with epilepsy.
What is the role of inhibitory synaptic inputs in the brain?
To control excitability and prevent overexcitation, which can lead to conditions like seizures.
How does the type of receptor influence synaptic response?
Isotropic receptors directly alter ion flow, while metabotropic receptors trigger slower, indirect effects through second messengers.
What is the key threshold concept for action potential generation?
The membrane potential must reach a point where sodium influx exceeds potassium efflux to trigger voltage-gated sodium channel activation.
What is meant by ‘frequency modulation’ in synaptic signaling?
The strength of a signal is communicated by the frequency of action potentials rather than their size.
What is the ‘active zone’ in a synapse?
The region in the presynaptic terminal where neurotransmitter vesicles cluster and fuse with the membrane to release their contents.
What is the postsynaptic density?
A thickened region of the postsynaptic membrane containing proteins, receptors, and intracellular signaling machinery.
What are the different types of synaptic arrangements mentioned?
Axodendritic, axosomatic, and axoaxonic synapses.
What is the significance of axosomatic synapses?
They are more influential in determining whether a neurone will generate an action potential.
What is the relationship between synaptic location and influence?
Synaptic inputs closer to the axon hillock have a greater impact on action potential generation.
How does the brain prevent overexcitation?
Through inhibitory inputs and control mechanisms that prevent excessive neuronal firing.
What is the role of chloride ions in inhibitory signaling?
Chloride influx leads to hyperpolarization, reducing the likelihood of action potential generation.
What is excitatory postsynaptic potential (EPSP)?
A depolarizing event caused by excitatory synaptic input, increasing the likelihood of an action potential.
What is inhibitory postsynaptic potential (IPSP)?
A hyperpolarizing event caused by inhibitory synaptic input, decreasing the likelihood of an action potential.
How do multiple EPSPs summate to generate an action potential?
Through spatial or temporal summation, where individual EPSPs combine to reach the threshold potential.
What are quantum synaptic events?
The smallest unit of neurotransmitter release, involving a single vesicle of neurotransmitter.
How does synaptic integration influence neural output?
The neurone integrates all excitatory and inhibitory inputs to determine if it reaches the threshold to fire an action potential.
What is the absolute refractory period?
The time during which no new action potential can be initiated, regardless of the stimulus strength.
What is the relative refractory period?
The time during which a stronger-than-normal stimulus is required to trigger another action potential.
Why are action potentials considered ‘all-or-nothing’ events?
Because their amplitude does not vary with the strength of the stimulus once the threshold is reached.
What is meant by ‘frequency encoding’ in neuronal signaling?
The strength of a stimulus is conveyed by the frequency of action potentials rather than changes in their size.
What limits the maximum frequency of action potentials?
The duration of the absolute refractory period.
What is the role of G-protein coupled receptors in synaptic signaling?
They trigger slower, longer-lasting intracellular responses through secondary messenger cascades.
How does synaptic diversity contribute to neural function?
Different synaptic arrangements and mechanisms allow for varied and precise control of neuronal communication.
What are ligand-gated ion channels?
Ion channels that open in response to the binding of a neurotransmitter, allowing specific ions to flow through the membrane.
What causes depolarization in an excitatory synaptic event?
Sodium influx into the postsynaptic neurone through ligand-gated ion channels.
How does an inhibitory synapse affect the postsynaptic membrane potential?
It causes hyperpolarization, making the membrane potential more negative and reducing excitability.
What is meant by ‘integration of synaptic inputs’?
The process by which a neurone combines multiple excitatory and inhibitory inputs to determine its output.
What role does the dendritic tree play in synaptic input?
It collects and processes signals from synaptic inputs across its branches, influencing neuronal activity.
What is the significance of the threshold potential?
It is the critical level of depolarization needed to trigger an action potential.
What happens when the threshold is reached in a neurone?
Voltage-gated sodium channels open, causing a rapid influx of sodium and the generation of an action potential.
How does epilepsy relate to synaptic signaling?
It involves excessive neuronal excitation and synchronization, leading to seizures.
What is the role of voltage-gated sodium channels in action potentials?
They allow sodium ions to enter the neurone during depolarization, driving the action potential.
What happens to voltage-gated sodium channels during the absolute refractory period?
They become inactivated and cannot open, preventing another action potential.
How do spatial summation and temporal summation differ?
Spatial summation combines inputs from multiple synapses, while temporal summation combines inputs from repeated activity at the same synapse.
What is excitotoxicity?
Neuronal damage or death caused by excessive stimulation and calcium influx.
What is the role of neurotransmitter vesicles in synaptic transmission?
They store and release neurotransmitters into the synaptic cleft during exocytosis.
How does chloride influx contribute to inhibitory signaling?
It increases the negative charge inside the neurone, hyperpolarizing the membrane and reducing excitability.
Why is frequency modulation important in neuronal communication?
It encodes the strength of a stimulus through the frequency of action potentials.
How does the relative refractory period allow for action potentials to occur?
With a strong enough stimulus, sufficient depolarization can occur to reach the threshold despite the hyperpolarized state.
What is a neuromuscular junction?
A specialized synapse where a motor neurone communicates with a muscle fiber.
What is the difference between excitatory and inhibitory postsynaptic potentials?
Excitatory potentials depolarize the membrane, while inhibitory potentials hyperpolarize it.
What mechanisms prevent overexcitation in the brain?
Inhibitory synapses, chloride influx, and control of excitatory inputs.
