Structure and Function of Neurons

Introduction

• Overview of neuron structure and function
• Importance of understanding structural components
• Functional relevance of neuron components

Structural Components of a Neuron

Dendrites

• Extensions from the neuron
• Receptive zones for other neurons

Cell Body (Soma)

• Contains the nucleus and other organelles
• Involved in protein synthesis

Axon

• Long extension connecting cell body to axon terminal
• Conducts action potentials
• Contains a subcomponent called the axon hillock, a site for action potential initiation

Axon Terminal

• Bulbous end of the neuron
• Involved in releasing neurotransmitters

Functions of Neuron Components

Dendrites

• Contain ligand-gated ion channels
  • Involved in formation of EPSPs (excitatory post-synaptic potentials) and IPSPs (inhibitory post-synaptic potentials)
  • Depolarization: Positive ion influx, stimulates action potentials
  • Hyperpolarization: Negative ion influx, inhibits action potentials
• Graded potentials via ligand-gated channels and G-protein-coupled receptors

Cell Body (Soma)

• Also involved in graded potentials
• Protein synthesis:
  • Process involves transcription of DNA to mRNA, translation on rough ER (Nissl bodies), and modification in Golgi apparatus
  • Produces neurotransmitters, enzymes, membrane proteins

Axon

• Conducts action potentials
  • Depolarization: Positive charge moves down the axon
  • Repolarization: Negative charge stabilizes the axon
• Axonal transport via microtubules and motor proteins (kinesin and dynein)
  • Anterograde transport (kinesin): Moves vesicles, mitochondria, from cell body to axon terminal
  • Retrograde transport (dynein): Moves damaged organelles, growth factors from axon terminal to cell body
• Pathogen exploitation of axonal transport (e.g., herpes, rabies)

Axon Terminal

• Secretory region for neurotransmitter release
• Re-uptake of neurotransmitters
• Involvement of SNARE proteins in vesicle fusion and neurotransmitter release
• Clinical relevance: SSRIs (Selective Serotonin Reuptake Inhibitors)

Classification of Neurons

Structural Classification

• Multipolar Neurons: Multiple dendrites, one axon (e.g., motor cortex, cerebellum)
• Bipolar Neurons: One dendrite, one axon (e.g., in retina, olfactory epithelium)
• Pseudo-unipolar Neurons: Single process dividing into peripheral and central processes (e.g., dorsal root ganglia)

Functional Classification

• Sensory Neurons
  • General Visceral Afferent: From visceral organs to CNS
  • General Somatic Afferent: From skin, muscles, joints to CNS
  • Special Sensory Afferent: From eyes, ears to CNS
  • Special Visceral Afferent: From smell, taste to CNS
• Motor Neurons
  • General Visceral Efferent: From CNS to visceral organs
  • General Somatic Efferent: From CNS to skeletal muscles
  • Special Visceral Efferent: To muscles derived from pharyngeal arches
• Interneurons
  • Located between sensory and motor neurons
  • Involved in reflexes and relay of information within CNS

Conclusion

• Recap of neuron structure and function
• Importance of understanding different neuron types and their roles in the nervous system