Fundamentals of the Nervous System

Overview

• Discussion on Chapter 11: The Fundamentals of the Nervous System
• Focus on physiology of graded potentials, action potentials, and chemical synapse

Neuronal Structure

• Neuron Anatomy
  • Soma (cell body) and dendrites: Receptive regions
  • Axon Hillock: Action potential initiation site
  • Axon: Conducting region
  • Axon Terminals: Secretory regions releasing neurotransmitters

Graded Potentials

• Stimulus Response

  • Dendrites and soma respond to stimuli: pressure, touch, vibration, stretch, temperature, pain, light, or chemicals
  • Transduction of stimuli into graded potentials (voltage changes)

• Types of Graded Potentials

  • EPSP (Excitatory Postsynaptic Potential)
    • Depolarization moving toward threshold (e.g., -55 mV)
    • Created by opening sodium channels (more Na+ enters than K+ leaves)
  • IPSP (Inhibitory Postsynaptic Potential)
    • Hyperpolarization moving away from threshold (more negative)
    • Created by opening potassium or chloride channels (K+ leaves, Cl- enters)

Action Potentials

• Threshold and Propagation

  • EPSP reaching threshold at the axon hillock triggers an action potential
  • Action potential propagates along the axon

• Channel Involvement

  • Voltage-Gated Sodium Channels: Open upon reaching threshold, causing depolarization
  • Voltage-Gated Potassium Channels: Open during repolarization phase

Chemical Synapse

• Process

  • Action potential reaches axon terminal
  • Voltage-gated calcium channels open
  • Neurotransmitters released into synaptic cleft
  • Neurotransmitters bind to postsynaptic receptors (EPSP/IPSP generation)

• Types of Synapses

  • Axosomatic: Axon to soma
  • Axodendritic: Axon to dendrite
  • Axoaxonic: Axon to axon
  • Chemical Synapse: Neurotransmitter-mediated communication

Integration and Summation

• Types of Summation

  • Temporal Summation: Multiple EPSPs from one synapse over time
  • Spatial Summation: Multiple synapses generating EPSPs simultaneously
  • E/I Balance: EPSPs can be countered by IPSPs

• Synaptic Potentiation

  • Enhanced synaptic transmission efficiency with repeated use
  • Important for learning and memory

Neural Processing

• Neuronal Pools

  • Discharge Zone: High probability of threshold crossing
  • Facilitated Zone: Lower probability, needs stronger input

• Processing Patterns

  • Serial Processing: Reflex arcs, linear transmission
  • Parallel Processing: Complex processing in CNS, multiple pathways

• Circuit Types

  • Diverging Circuit: One input, multiple outputs
  • Converging Circuit: Multiple inputs, single output
  • Reverberating Circuit: Oscillating paths for rhythmic activities
  • Parallel After Discharge: Complex problem-solving, multiple paths

Conclusion

• Understanding the difference between action potentials and graded potentials
• Recognition of chemical synapse complexity
• Appreciation for nervous system's role in simple to complex functions