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The Neuron: Structure and Function

This introduction to neurophilosophy explores the structure and function of neurons, including glia and the neuron doctrine. It covers topics such as the prototypical neuron, the neuronal membrane, axons and dendrites, synaptic transmission, and neuron classification.

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The Neuron: Structure and Function

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  1. Introduction • “Neurophilosophy” • Brain is the origin of mental abilities • Glia and Neurons • Glia: Insulates, supports, and nourishes neurons • Neurons • Process information • Sense environmental changes • Communicate changes to other neurons • Command body response

  2. The Neuron Doctrine • Histology • Study of tissue structure • The Nissl Stain • Facilitates the study of cytoarchitecture in the CNS

  3. The Neuron Doctrine • Golgi-stain (Developed by Camillo Golgi) shows two parts of neurons: • Soma and perikaryon • Neurites: Axons and dendrites

  4. The Neuron Doctrine • Cajal’s Contribution • Neural circuitry • Neurons communicate by contact, not continuity • Neuron doctrine • Neurons adhere to cell theory • Based in Golgi stain

  5. The Prototypical Neuron • The Nucleus • Gene expression • Transcription • RNA processing

  6. The Prototypical Neuron • The Soma • Cytosol: Watery fluid inside the cell • Organelles: Membrane-enclosed structures within the soma • Cytoplasm: Contents within a cell membrane (e.g., organelles, excluding the nucleus)

  7. The Prototypical Neuron • The Soma • Major site for protein synthesis • Rough endoplasmic reticulum

  8. The Prototypical Neuron • The Soma • Protein synthesis also on free ribosomes; polyribosomes

  9. The Prototypical Neuron • The Soma • Smooth ER and Golgi Apparatus • Sites for preparing/sorting proteins for delivery to different cell regions (trafficking) and regulating substances

  10. The Prototypical Neuron • The Soma • Mitochondrion • Site of cellular respiration (inhale and exhale) • Krebs cycle • ATP- cell’s energy source

  11. The Prototypical Neuron • The Neuronal Membrane • Barrier that encloses cytoplasm • ~5 nm thick • Protein concentration in membrane varies • Structure of discrete membrane regions influences neuronal function

  12. The Prototypical Neuron • The Cytoskeleton • Not static • Internal scaffolding of neuronal membrane • Three “bones” • Microtubules • Microfilaments • Neurofilaments

  13. The Prototypical Neuron • The Axon • Axon hillock (beginning) • Axon proper (middle) • Axon terminal (end) • Differences between axon and soma • ER does not extend into axon • Protein composition: Unique

  14. The Prototypical Neuron • The Axon • The Axon Terminal • Differences between the cytoplasm of axon terminal and axon • No microtubules in terminal • Presence of synaptic vesicles • Abundance of membrane proteins • Large number of mitochondria

  15. The Prototypical Neuron • The Axon • Synapse • Synaptic transmission • Electrical-to-chemical-to-electrical transformation • Synaptic transmission dysfunction • Mental disorders

  16. The Prototypical Neuron • The Axon • Axoplasmic transport • Anterograde (soma to terminal) vs. Retrograde (terminal to soma) transport

  17. The Prototypical Neuron • Dendrites • “Antennae” of neurons • Dendritic tree • Synapse - receptors • Dendritic spines • Postsynaptic (receives signals from axon terminal)

  18. Classifying Neurons • Classification Based on the Number of Neurites • Single neurite • Unipolar • Two or more neurites • Bipolar- two • Multipolar- more than two

  19. Classifying Neurons • Classification Based on Dendritic and Somatic Morphologies • Stellate cells (star-shaped) and pyramidal cells (pyramid-shaped) • Spiny or aspinous

  20. Classifying Neurons • Further Classification • By connections within the CNS • Primary sensory neurons, motor neurons, interneurons • Based on axonal length • Golgi Type I • Golgi Type II • Based on neurotransmitter type • e.g., – Cholinergic = Acetycholine at synapses

  21. Glia • Function of Glia • Supports neuronal functions • Astrocytes • Most numerous glia in the brain • Fill spaces between neurons • Influence neurite growth • Regulate chemical content of extracellular space

  22. Glia • Myelinating Glia • Oligodendroglia (in CNS) • Schwann cells (in PNS) • Insulate axons

  23. Glia • Myelinating Glia (Cont’d) • Oligodendroglial cells • Node of Ranvier • Region where the axonal membrane is exposed

  24. Glia • Other Non-Neuronal Cells • Microglia as phagocytes (immune)

  25. Structure Correlates with Function NEURONS Soma Axons Dendrites Synapse Structural characteristics of a neuron tell us about its function e.g., Dense Nissl stain = protein; suggestsspecialization Elaborate structure of dendritic tree = receiver

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