Neuron Action Potential and Spatial Summation

Overview

• Determining if a neuron will reach action potential involves interpreting incoming information from numerous synaptic connections.
• A neuron may receive input from up to 10,000 synaptic knobs.

Key Concepts

Postsynaptic Neuron

• A neuron that receives signals through dendrites and soma from presynaptic neurons.
• Must perform spatial summation:
  • This involves adding together the effects of all presynaptic neurons.

Types of Postsynaptic Potentials

1. Excitatory Postsynaptic Potentials (EPSPs):
   • Neurotransmitters that depolarize the postsynaptic neuron increasing the likelihood of action potential.
2. Inhibitory Postsynaptic Potentials (IPSPs):
   • Neurotransmitters that inhibit the postsynaptic neuron, decreasing the likelihood of action potential.

Axon Hillock

• The only area of a neuron that can generate an action potential.
• Known as the trigger zone.
• An action potential is generated only when the axon hillock depolarizes to threshold.

Factors Influencing Action Potential

• Depolarization in other parts (like dendrites) affects membrane potential but not action potential generation.
• Cumulative Effect of EPSPs and IPSPs must depolarize the axon hillock to threshold for action potential.

Influence of Synaptic Knobs

• Proximity to Axon Hillock:
  • Closer synaptic knobs have a greater influence on action potential generation.
  • Synaptic knobs terminating in dendrites have a lesser effect.

Spatial Summation

• The process of adding together the cumulative effects of many synaptic knobs.
• Position of synaptic knobs is critical: the closer to the axon hillock, the greater the effect.