Action Potential: Determined by whether the neuron can depolarize to threshold voltage at the axon hillock.
Postsynaptic Neuron: The neuron that receives signals at synapses and must interpret these to decide on action potential.
Synaptic Inputs
Synaptic Knobs: Postsynaptic neuron may have up to 10,000 synaptic knobs from other neurons.
Neurotransmitters:
EPSPs (Excitatory Postsynaptic Potentials): Neurotransmitters that depolarize and excite the neuron, increasing the likelihood of reaching action potential.
IPSPs (Inhibitory Postsynaptic Potentials): Neurotransmitters that inhibit the neuron, decreasing the likelihood of reaching action potential.
Mechanism of Action Potential Generation
Axon Hillock (Trigger Zone):
The only section of the postsynaptic neuron capable of generating an action potential.
Depolarization must reach the threshold at this zone to generate an action potential.
Depolarization in dendrites affects membrane potential but doesn't cause action potential.
Spatial Summation
Summation Process:
Involves adding the effects of EPSPs and IPSPs from numerous synaptic inputs.
Determines if depolarization at the axon hillock is sufficient to reach threshold.
Factors Influencing Spatial Summation
Proximity to Axon Hillock:
Synaptic knobs closer to the axon hillock have a greater effect on action potential generation.
Synaptic knobs on distal dendrites have a lesser influence.
Conclusion
The decision for a neuron to fire an action potential is dependent on spatial summation, where position and cumulative synaptic input are crucial factors.