Structure and Function of Neurons

Introduction

• Discussed the structure and function of neurons
• Reminder to like, comment, and subscribe
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Components of a Neuron

• Dendrites: Extensions off the neuron; receptive zone
• Cell Body (Soma): Central, circular structure
• Axon: Long elongated part between cell body and axon terminal
  • Axon Hillock: Narrows from cell body to axon; crucial for action potentials
• Axon Terminal: Bulbous structure at end; also called synaptic terminal or bulb

Functions of Neuron Components

Dendrites

• Receptive zones for signals from other neurons
• Contain ligand-gated ion channels (LGIC) involved in EPSPs and IPSPs
  • EPSP (Excitatory Post-Synaptic Potential): Positive ions enter, cell depolarizes
  • IPSP (Inhibitory Post-Synaptic Potential): Negative ions enter, cell hyperpolarizes
• G-Protein Coupled Receptors (GPCR) also present for graded potentials through second messengers

Cell Body (Soma)

• Similar to dendrites in generating graded potentials
• Primary role in protein synthesis
  • DNA transcribed to mRNA, translated into proteins at rough ER (Nissl bodies)
  • Processed and packaged by Golgi apparatus
  • Proteins include neurotransmitters, enzymes, and membrane proteins

Axon

• Conducts action potentials: depolarization (positive charge) followed by repolarization (negative charge)
• Axonal Transport via microtubules and motor proteins
  • Kinesin: Anterograde transport (cell body to axon terminal)
  • Dynein: Retrograde transport (axon terminal to cell body)
• Neurotransmitters, mitochondria, and other organelles are transported
• Pathogens can exploit transport (e.g., herpes, rabies)

Axon Terminal

• Secretory region: releases neurotransmitters
• Reuptake of neurotransmitters for recycling
• SNARE proteins facilitate vesicle fusion for neurotransmitter release
• Neurotransmitter termination by reuptake or degradation
  • Clinical Relevance: SSRIs inhibit serotonin reuptake

Neuron Classification

Structural Classification

• Multipolar Neurons: Multiple dendrites, one axon; found in motor cortex and cerebellum
  • Examples: Pyramidal cells (motor cortex), Purkinje cells (cerebellum)
• Bipolar Neurons: One dendrite, one axon; found in retina, olfactory epithelium, inner ear
• Pseudo-Unipolar Neurons: Peripheral and central processes; found in dorsal root ganglion (DRG) and trigeminal ganglion

Functional Classification

• Sensory (Afferent) Neurons
  • General Visceral Afferent (GVA): From visceral organs to CNS
  • General Somatic Afferent (GSA): From skin/muscle/joints to CNS
  • Special Sensory Afferent (SSA): From eyes/ears to CNS
  • Special Visceral Afferent (SVA): From smell/taste to CNS
• Motor (Efferent) Neurons
  • General Visceral Efferent (GVE): From CNS to smooth/cardiac muscle, glands
  • General Somatic Efferent (GSE): From CNS to skeletal muscles
  • Special Visceral Efferent (SVE): To head/neck muscle (cranial nerves V, VII, IX, X)
• Interneurons: Relay between sensory and motor neurons; widespread in CNS