Neuronal Communication and Signal Transmission

Overview

• Neurons must communicate for graded potentials or action potentials to occur.
• Involves pre-synaptic (sending signal) and post-synaptic (receiving signal) neurons.
• Synaptic cleft: space between neurons.

Types of Neuronal Communication

• Axodendritic: Axon of pre-synaptic neuron communicates with dendrites of post-synaptic neuron.
• Axosomatic: Axon of pre-synaptic neuron communicates with soma (cell body) of the post-synaptic neuron.
• Axoaxonic: Axon of pre-synaptic neuron communicates with axon hillock of the post.

Synapse Process

• Presynaptic neuron sends an action potential (AP) down its axon.
• AP causes a change in charge (negative 70mV to positive 30mV) leading to calcium voltage gates opening.
• Calcium influx causes release of neurotransmitters into synaptic cleft.
• Neurotransmitters diffuse across the cleft to the post-synaptic neuron.
• Neurotransmitters bind to ligand-gated channels on post-synaptic neuron.
  • This opens the channels, allowing ions like sodium to enter, causing a graded potential.
• Graded potentials summate to reach threshold (negative 55mV) at axon hillock, generating a new AP.

Types of Summation

• Spatial Summation:
  • Multiple presynaptic neurons target one postsynaptic neuron.
  • Signals sent rapidly; threshold reached quickly (e.g., negative 55mV at hillock).
• Temporal Summation:
  • One presynaptic neuron repeatedly sends signals to one postsynaptic neuron.
  • Takes longer to reach threshold.

Examples and Analogies

• Spatial vs. Temporal Summation:
  • Spatial is faster, likened to multiple people digging a hole together vs. one person.
• Excitatory and Inhibitory Potentials:
  • Excitatory Post-Synaptic Potentials (EPSPs): Depolarize, increase likelihood of AP.
  • Inhibitory Post-Synaptic Potentials (IPSPs): Hyperpolarize, decrease likelihood of AP.
  • Net summation of EPSPs and IPSPs determines AP generation.