Overview
This lecture covers how groups of neurons (functional groups or pools) are connected in the central nervous system, focusing on integration, circuit types, and regulation mechanisms.
Functional Groups of Neurons
- Functional groups (or pools) of neurons are collections of interconnected interneurons for specific processes.
- These groups are defined by their connections and functions such as movement or memory processing.
- Integration in the CNS relies on the organization of these interconnected circuits.
Types of Neural Circuits
- Diverging circuits start with one input neuron and spread the signal to multiple output neurons (like a phone tree).
- Diverging circuits amplify signals, enabling one neuron to affect many downstream targets (e.g., upper motor neuron activating multiple muscle units).
- Converging circuits have multiple input neurons signaling to a single output neuron.
- Converging circuits allow the integration of information from different sources into one pathway (e.g., multiple sensory inputs converging onto one neuron).
Circuit Regulation and Stability
- Positive feedback amplifies signals but can destabilize circuits.
- Negative (inhibitory) feedback stabilizes circuits by shutting them off after achieving the desired outcome.
- Synaptic fatigue occurs when overstimulated neurons transmit weaker signals due to excessive activity.
- Upregulation increases receptor availability when stimulus is low; downregulation decreases receptors when stimulus is constant.
Key Terms & Definitions
- Integration — The process of connecting and coordinating neuron activity for specific functions.
- Interneuron — A neuron connecting other neurons within the central nervous system.
- Diverging Circuit — A neural circuit where one input leads to multiple outputs.
- Converging Circuit — A neural circuit where multiple inputs come together on a single neuron.
- Positive Feedback — Mechanism amplifying signals within a circuit.
- Negative Feedback — Mechanism inhibiting or terminating signals to stabilize circuits.
- Synaptic Fatigue — Weakened signal transmission due to repeated neuron stimulation.
- Upregulation/Downregulation — Increase or decrease of receptor numbers on neurons in response to changes in stimulation.
Action Items / Next Steps
- Prepare for next chapter (12): Study the central nervous system.
- Review these types of circuits and related terminology for understanding CNS integration.