physio - synapses

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.