Synapsis III (Processing of signal in nervous system)

📖 Synaptic Processing & Neuronal Pool

🖇 Neuronal Pool = Collection of neurons inside the CNS responsible for processing signals (Plasticity).

🟠 I. Neuronal Pool Fields

📌 Excitatory Field

• Discharge Zone (Central):
• • High number of synapses + large amount of neurotransmitter.
  • Generates a true AP.
• Facilitatory Zone (Peripheral):
• • Fewer synapses + less neurotransmitter.
  • Only PSPs, not strong enough for AP (neurons are “facilitated”).

📌 Inhibitory Field

• Stronger inhibition in the center, weaker at the periphery.

🟣 II. Neural Signal Processing Mechanisms

1. 🚨 Divergence (Signal Spreading)

• Amplifying Divergence: All outputs serve the same function → stronger response.
• • Example: Pyramidal tract axon → many anterior horn cells → full muscle contraction.
• Diversifying Divergence: Outputs head in different directions with different functions.
• • Example: Proprioception → Cerebellum (balance) + Sensory cortex (conscious sensation).

2. 🚨 Convergence (Signal Integration)

• From the same source: Multiple terminals from one input neuron → summation → AP.
• From multiple sources: Different inputs converge → integrated response.
• • Example: Sensory + auditory + visual inputs → decision center in brain.

3. 🚨 Prolongation of Signal

• Synaptic After-Discharge: Long-acting transmitter (e.g., Substance P).
• Parallel Circuits: Different-length pathways → successive output impulses.
• Reverberating Circuits: Closed loop with positive feedback.
• • Examples: Vascular tone, GI tone, Respiratory rhythm.

4. 🚨 Shortening of Signal (Termination)

• Negative Feedback Inhibition: Output neuron collateral → inhibitory interneuron → inhibits the same neuron.
• • Example: Renshaw cells in spinal cord.
• Feed-Forward Inhibition: Input excites both output neuron + inhibitory interneuron → fast inhibition.
• • Example: Purkinje cells in cerebellum (dampening/“braking” function).

5. 🚨 Sharpening of Signal (Precision)

• Lateral Inhibition: Main pathway inhibits adjacent ones.
• • Examples:
  • • Renshaw cells (spinal cord).
    • Horizontal cells (retina).
• Reciprocal Inhibition: Agonist contraction + Antagonist inhibition.
• • Example: Flexor Withdrawal Reflex (Biceps contract, Triceps inhibited).

📌 Key Lecturer Emphasis

• ⚡ Difference between Discharge Zone vs Facilitatory Zone.
• ⚡ Difference between Amplifying vs Diversifying Divergence.
• ⚡ Difference between Parallel Circuits vs Reverberating Circuits.
• ⚡ Specific examples: Renshaw cells (Negative feedback & Lateral inhibition), Purkinje cells (Feed-forward inhibition).
• ⚡ Classic example of Reciprocal Inhibition = Flexor Withdrawal Reflex.