Structure and Function of Neurons

Introduction

• Video Speaker: Ninja Nerds
• Topic: Structure and Function of Neurons
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Structural Components of a Neuron

1. Dendrites
   • Extensions from the neuron, called receptive zones.
2. Cell Body (Soma)
   • Circular structure housing the nucleus and various organelles.
3. Axon
   • Long, elongated portion of the neuron.
   • Special part: Axon Hillock (high concentration of voltage-gated sodium channels).
4. Axon Terminal (Synaptic Terminal/Bulb)
   • Bulbous structure at the end of the axon.

Functions of Neuronal Components

Dendrites

• Receptive Zone: Receives signals from other neurons.
• Ligand-Gated Ion Channels: Formation of EPSPs (Excitatory Post-Synaptic Potentials) and IPSPs (Inhibitory Post-Synaptic Potentials).
• Graded Potentials: Small changes in membrane voltage that help generate action potentials.
• G-Protein Coupled Receptors: Activate second messengers and protein kinases for various cellular responses.

Cell Body (Soma)

1. Graded Potentials: Shared function with dendrites.
2. Protein Synthesis: Major Function
   • Rough Endoplasmic Reticulum (Nissl Bodies): Translation of mRNA to proteins.
   • Golgi Apparatus: Protein modification and packaging.

Axon

• Action Potentials: Electrical currents that travel from the cell body to the axon terminal.
• Phases of Action Potentials: Depolarization followed by repolarization.
• Motor Proteins: Kinesin (anterograde transport) and dynein (retrograde transport).
• Axonal Transport: Movement of vesicles, organelles, and other cellular components.

Microtubules and Motor Proteins

• Kinesin: Transports vesicles containing neurotransmitters, mitochondria, etc., from cell body to axon terminal.
• Dynein: Transports degraded or used materials back up to the cell body.
• Clinical Relevance: Pathogens like polio and herpes viruses utilize these pathways.

Axon Terminal

• Secretory Region: Release and reuptake of neurotransmitters.
• Voltage-Gated Calcium Channels: Allow calcium influx, triggering neurotransmitter release.
• SNARE Proteins: Facilitate vesicle fusion with the axonal membrane for neurotransmitter release.
• Neurotransmitter Termination: Done by degradation or reuptake.
  • Reuptake Mechanism: Important for recycling neurotransmitters and impacted by SSRIs.

Neuronal Classifications

Structural Classification

1. Multipolar Neurons
   • Multiple dendritic extensions, found in areas requiring multiple inputs (e.g., motor cortex, cerebellum).
2. Bipolar Neurons
   • One dendritic extension and one axon, found in special sensory organs (e.g., retina, olfactory epithelium).
3. Pseudo-Unipolar Neurons:
   • Peripheral and central processes with the cell body in between.
   • Found in dorsal root ganglia and cranial nerves.

Functional Classification

1. Sensory Neurons (Afferent)
   • General Visceral Afferent (GVA): From visceral organs.
   • General Somatic Afferent (GSA): From skin, muscles, joints.
   • Special Sensory Afferent (SSA): From vision and hearing organs.
   • Special Visceral Afferent (SVA): From taste and smell sensors.
2. Motor Neurons (Efferent)
   • General Visceral Efferent (GVE): To visceral organs.
   • General Somatic Efferent (GSE): To skeletal muscles.
   • Special Visceral Efferent (SVE): To head and neck muscles derived from pharyngeal arches.
3. Interneurons
   • Connect sensory and motor pathways; predominantly found in the brain and spinal cord.

Conclusion

• Summary: Covered the structure and function of different neuron parts.
• Further Research: Graded potentials, action potentials, protein synthesis in neurons.
• Importance: Understanding neurons' structure/function is crucial for grasping neurological concepts.