Understanding Neurons and Their Functions

Sep 8, 2024

Biological Basis of Behavior: Structure and Function of Neurons

Lecture Introduction

  • Video Series: 5-part series on neuron structure and function.
  • Video Format: Interactive videos with questions or one long video.
  • Objectives:
    • Identify parts of neurons.
    • Understand communication within and between neurons.
    • Measure action potentials.
    • Explain ion dynamics and role in membrane potential.
    • Describe neurotransmission and postsynaptic potentials.

Neuron Structure and Function

Neuron Anatomy

  • Dendrites: Input area; listen for signals.
  • Soma (Cell Body): Decision-making; site of molecular activity.
  • Axon Hillock: Junction for action potential initiation.
  • Axon: Transmits signals to terminal buttons.
  • Terminal Buttons: Output area; release neurotransmitters.
  • Synapse: Gap between terminal button of one neuron and dendrite of another.

Types of Neurons

  • Multipolar Neurons: Common in CNS; many dendrites, complex.
  • Bipolar Neurons: Found in sensory pathways; simpler structure.
  • Unipolar Neurons: Simple sensory neurons; cell body on periphery.

Glial Cells

Types of Glial Cells

  • Astrocytes:
    • Connect to blood vessels, part of blood-brain barrier.
    • Provide support and nutrition to neurons.
    • Remove debris.
  • Oligodendrocytes:
    • Produce myelin in CNS.
    • Wrap around multiple axons.
  • Schwann Cells:
    • Produce myelin in PNS.
    • One-to-one relationship with axons.
  • Microglia:
    • Act as phagocytes; remove waste and pathogens.

Membrane Potential and Ion Dynamics

Membrane Potential

  • Concept: Energy stored due to ion distribution.
  • Key Ions:
    • Potassium (K+): Higher inside cell, diffuses out.
    • Sodium (Na+): Higher outside, diffuses in.
    • Chloride (Cl-): Higher outside, diffuses in.
  • Sodium-Potassium Pump: Maintains potential by pumping 3 Na+ out, 2 K+ in.

Ion Channels

  • Voltage-Gated Channels: Open with changes in membrane potential.
  • Ligand-Gated Channels: Open upon neurotransmitter binding.

Action Potentials

Action Potential Mechanism

  • Stages:
    • Depolarization: Na+ influx raises potential.
    • Repolarization: K+ efflux lowers potential.
    • Refractory Period: Na+ channels inactive, resetting.
  • All-or-None Law: Action potentials happen completely or not at all.

Signal Propagation

  • Saltatory Conduction: Signal jumps between nodes of Ranvier in myelinated axons.
  • Rate Law: Intensity coded by rate of action potentials.

Neurotransmission and Synaptic Function

Synapse Structure

  • Synaptic Cleft: Gap between neurons.
  • Presynaptic Membrane: Releases neurotransmitter.
  • Postsynaptic Membrane: Contains receptors.

Neurotransmitter Release

  • Action Potential Arrival: Opens Ca2+ channels.
  • Vesicle Docking: Fusion with membrane, releasing neurotransmitter.

Postsynaptic Potentials

  • Excitatory (EPSPs): Na+ inflow depolarizes, potentially triggering action potential.
  • Inhibitory (IPSPs): Cl- inflow or K+ outflow hyperpolarizes, inhibiting action potential.

Termination of Synaptic Transmission

  • Reuptake: Neurotransmitter reabsorbed by presynaptic neuron or astrocytes.
  • Enzymatic Degradation: Neurotransmitter broken down in synaptic cleft.

Receptor Types

  • Ionotropic Receptors: Directly open ion channels; fast response.
  • Metabotropic Receptors: Indirect, involve G-proteins; slower, longer-term effects.

This summary captures the key points from the lecture on the biological basis of behavior focusing on the structure and function of neurons. It covers neuron anatomy, types of neurons and glial cells, membrane potentials, action potentials, and neurotransmission processes.