Neurobiology Lecture - Key Concepts

I. Nerve Cells and Behavior

• Introduction

  • Complexity and Diversity

  • Nerve cells play crucial roles in understanding behavior through:

    • Information
    • Response
    • Sensory Input
    • Motor Output

  • Levels of organizational analysis include molecular, cellular, tissue, organ, organ system, individual, and population levels.

  • Feedback loops are essential for modulating responses.

  • Example considerations of feedback mechanisms.

• Integration and Association

  • Achieving greater control via:
  • Interneurons that provide integrative pathways.
  • Memory pathways enhance behavioral adaptation, enabling learning and adjustments.

• Complexity and Diversity (continued)

  • The level of complexity in nerve organization depends on:
  • Organism type: e.g., amoeba, leech, fish, osprey.
  • Environmental challenges which influence neural requirements.
  • Typical neuron counts in different species:
  • Human brain: ~10^{11} neurons
  • Snail brain: ~10^{4} neurons
  • C. elegans: ~10^{2} neurons.

• Connections Between Neurons

  • Each human neuron connects with approximately:
  • 10^3 other neurons, enhancing processing capabilities.
  • Synaptic zones identified in studies of neuron connections.

• Diversity of Neuron Types

  • In human brains, diversity estimates range from:
  • 10^{4} - 10^{5} neuron types, suggesting high parallel processing potential.
  • In snail brains, fewer types (~10^{2} - 10^{3}) limit redundancy and processing capacity.

• Reasons for Differences Among Organisms

  • Variability in brain function due to:
  • Behavioral repertoires.
  • Longevity and morphology.
  • The necessity for higher order functions.

II. Studying Complex Systems

• Neurobiology encompasses multiple research levels, each posing unique challenges and focal points:
  • Mechanisms of signal generation/transmission within neurons.
  • Neuron interconnections.
  • Relationships between connectivity patterns and behavior.
  • Modifications due to experiences or injuries.

III. Nervous System Organization

• Neurons

  • Early histological techniques uncovered neuron variability in structures.
  • Significant advancement by Camillo Golgi concerning silver ion staining to visualize neuron morphology, perfected by Santiago Ramon y Cajal.

• Neuron Structure

  • A typical vertebrate neuron consists of:
  • Cell Body (Soma): 10-50 μm in diameter.
  • Dendrites.
  • Axon: 0.2-20 μm in diameter.
  • Axon Terminals.

• Morphology Classification

  • Neurons can be categorized based on function:
  • Input: Receives signals.
  • Integration: Processes inputs and initiates conduction.
  • Conduction: Propagates action potentials.
  • Output: Signals to other neurons or effector cells.

• Electrochemical Signaling Components

  • Input: Local receptor signals elicited in dendrites.
  • Integration: Decision-making at the axon hillock, determines if action potential occurs based on local graded potentials.
  • Conduction: Active propagation of action potentials down the axon via voltage-gated channels.
  • Output: Release of neurotransmitters at axon terminals facilitated by calcium channels.

IV. Action Potentials vs. Local Signals

• Key Differences
  • Local signals (e.g., receptor potentials):
  • Small amplitude (0.1-10 mV), brief duration.
  • Show graded responses and passive propagation.
  • Action potentials:
  • Large amplitude (70-110 mV), all-or-none signal, active propagation through voltage-gated sodium channels.

V. Excitatory vs. Inhibitory Synapses

• Not all synaptic potentials are excitatory; some create hyperpolarizing effects, inhibiting action potential generation.
  • Examples observed in retinal ganglion cells illustrating different synaptic potentials.