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Q: What is a synapse?
A: A junction where neurons communicate with other neurons or effectors using neurotransmitters.
Q: What are the two types of synapses?
A:
1. Electrical synapses – Direct ion flow through gap junctions (fast, bidirectional).
2. Chemical synapses – Use neurotransmitters to send signals across a synaptic cleft (slower, unidirectional).
Q: What is the difference between pre-synaptic and post-synaptic neurons?
A:
• Pre-synaptic neuron: Releases neurotransmitter.
• Post-synaptic neuron: Receives neurotransmitter via receptors.
Q: What is the function of the synaptic cleft?
A: It is the space between neurons where neurotransmitters diffuse to relay the signal.
Q: What are the steps of synaptic transmission at a chemical synapse?
A:
1. Action potential arrives at the axon terminal.
2. Voltage-gated Ca²⁺ channels open → Ca²⁺ enters the presynaptic neuron.
3. Ca²⁺ triggers vesicle fusion with the membrane → Neurotransmitter release into the synaptic cleft.
4. Neurotransmitter binds to receptors on the postsynaptic membrane.
5. Postsynaptic response occurs (depolarization or hyperpolarization).
6. Neurotransmitter removal via reuptake, degradation, or diffusion.
Q: What is the role of Ca²⁺ in synaptic transmission?
A: It triggers vesicle fusion with the presynaptic membrane, leading to neurotransmitter release.
Q: What happens if Ca²⁺ channels are blocked?
A: Neurotransmitter release fails, preventing synaptic transmission.
Q: What is the neurotransmitter used in a nicotinic cholinergic synapse?
A: Acetylcholine (ACh).
Q: What receptor does ACh bind to in a nicotinic synapse?
A: Nicotinic acetylcholine receptor (nAChR), an ionotropic receptor.
Q: What happens when ACh binds to nAChR?
A: The receptor opens, allowing Na⁺ influx, causing depolarization (EPSP).
Q: How is ACh removed from the synaptic cleft?
A: By the enzyme acetylcholinesterase (AChE), which breaks it down into acetate and choline.
Q: What happens if AChE is inhibited (e.g., nerve gas, pesticides)?
A: ACh accumulates, leading to continuous depolarization and muscle paralysis.
Q: What are the two types of postsynaptic potentials?
A:
1. Excitatory postsynaptic potential (EPSP) – Depolarizes the neuron, increasing the likelihood of firing an AP.
2. Inhibitory postsynaptic potential (IPSP) – Hyperpolarizes the neuron, decreasing the likelihood of firing an AP.
Q: What ions are involved in EPSPs?
A: Na⁺ influx or Ca²⁺ influx.
Q: What ions are involved in IPSPs?
A: K⁺ efflux or Cl⁻ influx.
Q: Can EPSPs and IPSPs occur simultaneously?
A: Yes, the summation of EPSPs and IPSPs determines whether an AP will be generated.
Q: What are the two types of summation?
A:
1. Temporal summation – Repeated inputs from one presynaptic neuron.
2. Spatial summation – Multiple presynaptic neurons simultaneously stimulating a postsynaptic neuron.
Q: How does summation affect action potential generation?
A:
• If EPSPs > IPSPs → AP is triggered.
• If IPSPs > EPSPs → AP is inhibited.
Q: What happens if two EPSPs arrive at the same time?
A: The depolarization adds up, increasing the chance of reaching threshold.
Q: What happens if an EPSP and an IPSP arrive at the same time?
A: They cancel out, reducing the chance of an AP.
Q: What is presynaptic facilitation?
A: When one neuron enhances neurotransmitter release from another neuron.
Q: What is presynaptic inhibition?
A: When one neuron reduces neurotransmitter release from another neuron.
Q: How does presynaptic inhibition occur?
A: An inhibitory neuron blocks Ca²⁺ entry, preventing vesicle release.
Q: How does presynaptic facilitation occur?
A: A modulatory neuron increases Ca²⁺ entry, enhancing neurotransmitter release.
Q: What is convergence in neural circuits?
A: Multiple presynaptic neurons synapsing onto a single postsynaptic neuron.
Q: What is divergence in neural circuits?
A: A single presynaptic neuron branching to multiple postsynaptic neurons.
Q: What is the functional importance of convergence?
A: Allows a single neuron to integrate multiple inputs before firing an AP.
Q: What is the functional importance of divergence?
A: Allows a single neuron to spread its signal to multiple targets.
