Neuroscience Chapter on Synaptic Transmission

Study Notes

Action potential reaches the presynaptic terminal, opening voltage-gated calcium channels.
Calcium influx triggers synaptic vesicles to fuse with the membrane (exocytosis).
Neurotransmitters are released into the synaptic cleft, diffusing to the postsynaptic terminal.
Binding of neurotransmitters to neuroreceptors causes Na+ channels to open, leading to an influx of sodium ions.
If the threshold is reached, an action potential is initiated in the postsynaptic neuron.
Neurotransmitters are broken down by specific enzymes in the synaptic cleft.
Cholinergic synapses primarily release acetylcholine (ACh), facilitating information transfer across the synaptic cleft.
Synaptic delay occurs due to the time taken for calcium influx and neurotransmitter release.
Choline from broken down ACh is reabsorbed and recycled by presynaptic neurons.
Synaptic fatigue can occur when ACh stores are depleted.

Fundamental Classification:
- Chemical Synapse: Involves neurotransmitter release from presynaptic neurons to receptors on postsynaptic cells, influencing cell activity.
- Electrical Synapse: Direct connection between membranes allowing electrical current to pass, resulting in rapid signal transmission.
Working Classification:
- Excitatory Ion Channel Synapses: Neuroreceptors are Na+ channels; opening leads to local depolarization and potential action action.
- Inhibitory Ion Channels: Not detailed but typically reduce the likelihood of action potentials.
- Non-Channel Synapses: Function through different mechanisms, specifics not provided.
- Neuromuscular Junctions: Specialized connections between neurons and muscles.
- Electrical Synapses: Direct membrane contact allows for fast electrical signal transfer.

Resting membrane potential is approximately -65 millivolts.
Excitatory postsynaptic potential (EPSP) occurs when Na+ influx neutralizes negativity.
Action potentials require simultaneous activation of 40 to 80 terminals via a process called summation.
Spatial Summation: Summation of signals from multiple synaptic terminals activating widely spaced membrane areas.
Temporal Summation: Rapid firing from a single presynaptic terminal within a brief period enhances potential effects.

A neuron can receive thousands of synaptic inputs, leading to a collective effect known as the Grand Postsynaptic Potential (GPP).
GPP determines whether the neuron fires: more excitatory inputs than inhibitory ones will result in firing, while the reverse will inhibit it.
Neurons can exhibit “facilitation” when the summed potential approaches firing threshold but is insufficient; subsequent excitatory signals may easily trigger action potentials.

Axosomatic Synapse: Axon terminates on the soma of another neuron.
Axodendritic Synapse: Axon ends on the dendrite of the next neuron.
Axoaxonic Synapse: Axon terminates on another neuron's axon.
Dendrodendritic Synapse: Connections between dendrites of different neurons.