10 Minute Neuroscience: Neurons

Overview

• Neurons: Fundamental units of the nervous system.
• Function: Transmit and receive information; communicate with various tissues.
• Quantity: ~86 billion neurons in the human brain.
• Connectivity: Each neuron forms thousands of connections, creating complex circuitry.

Neuron Communication

• Signals: Utilize electrical and chemical signals.
• Action Potentials: Electrical impulses from ion flow.
• Neurotransmitters: Chemical signals facilitating communication.
• Rare exceptions: Some neurons communicate only electrically.

Neuron Structure

• Dendrites: Branch-like structures extending from the neuron.
  • Receive messages; contain receptors for neurotransmitters.
• Cell Body (Soma): Metabolic center with nucleus and organelles.
• Axon Hillock: Integrates signals to determine if action potential is initiated (summation).
• Axon: Conducts action potentials; varying lengths.
  • Myelin: Insulates axons, speeds up signal propagation.
  • Nodes of Ranvier: Gaps in myelin facilitating action potentials.
• Axon Terminals/Synaptic Boutons: Endings that communicate at synapses.
  • Synapse: Site of neuron communication; contains synaptic cleft.
  • Presynaptic & Postsynaptic Neurons: Neurons on either side of synaptic cleft.

Neuron Classification

• By Structure:

  • Multipolar Neurons: Most common; single axon, many dendrites.
  • Bipolar Neurons: Two extensions; one axon, one dendritic structure.
  • Unipolar Neurons: Single extension with branches.
  • Pseudo-unipolar Neurons: Single process from fused axon and dendrite.

• By Function:

  • Motor Neurons: Control movement; synapse with muscles.
  • Sensory Neurons: Carry sensory signals.
  • Interneurons: Vast majority; intermediaries between neurons.
    • Projection Interneurons: Long axons for long-distance signaling.
    • Local Interneurons: Short axons for nearby connections.

Conclusion

• Neurons have a standardized structure but vary significantly in form and function, allowing for diverse roles within the nervous system.
• Understanding neuron structure and classification helps comprehend their role in neural networks.