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Neuroscience: Exploring the Brain, 4e Chapter 2: Neurons and Glia Chapter 1: Applying Research to Everyday Exercise and Sport Copyright © 2015 Wolters Kluwer Health | Lippincott Williams & Wilkins Introduction • “Neurophilosophy” – No separation of mind and brain • Glia and neurons – Glia insulate, support, and nourish neurons. – Neurons • Process information • Sense environmental changes • Communicate changes to other neurons • Command body response Copyright © 2016 Wolters Kluwer • All Rights Reserved The Neuron Doctrine • Histology – Microscopic study of tissue structure – Nissl stain • Facilitates the study of cytoarchitecture in the CNS Copyright © 2016 Wolters Kluwer • All Rights Reserved The Neuron Doctrine—(cont.) • Golgi stain (developed by Camillo Golgi) revealed two parts of neurons: – Soma and perikaryon – Neurites: axons and dendrites Copyright © 2016 Wolters Kluwer • All Rights Reserved Basic Parts of a Neuron Copyright © 2016 Wolters Kluwer • All Rights Reserved The Neuron Doctrine—(cont.) • Cajal’s contribution – Neural circuitry – Neurons communicate by contact, not continuity. • Neuron doctrine • Neurons adhere to cell theory. • Use of Golgi stain Copyright © 2016 Wolters Kluwer • All Rights Reserved Neurites in Contact, Not Continuity Copyright © 2016 Wolters Kluwer • All Rights Reserved 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) Copyright © 2016 Wolters Kluwer • All Rights Reserved The Prototypical Neuron—(cont.) • The nucleus – Gene expression – Transcription – RNA processing Copyright © 2016 Wolters Kluwer • All Rights Reserved Internal Structure of a Typical Neuron Copyright © 2016 Wolters Kluwer • All Rights Reserved The Prototypical Neuron—(cont.) • Neuronal genes, genetic variation, and genetic engineering – Neurons differ from other cells because of specific genes. – Sequencing of human genome – Genetic basis of many diseases of the nervous system – Role of genetic engineering and gene targeting Copyright © 2016 Wolters Kluwer • All Rights Reserved The Prototypical Neuron—(cont.) • The soma—(cont.) – Ribosomes the major site for protein synthesis • Rough endoplasmic reticulum Copyright © 2016 Wolters Kluwer • All Rights Reserved The Prototypical Neuron—(cont.) • The soma—(cont.) – Protein synthesis also on free ribosomes; polyribosomes Copyright © 2016 Wolters Kluwer • All Rights Reserved The Prototypical Neuron—(cont.) • The soma—(cont.) – Smooth ER and Golgi apparatus • Sites for preparing/sorting proteins for delivery to different cell regions (trafficking) and regulating substances Copyright © 2016 Wolters Kluwer • All Rights Reserved The Prototypical Neuron—(cont.) • The soma—(cont.) – Mitochondria • Site of cellular respiration (inhale and exhale) • Krebs cycle • ATP is cell’s energy source. Copyright © 2016 Wolters Kluwer • All Rights Reserved The Prototypical Neuron—(cont.) • The neuronal membrane – Barrier that encloses cytoplasm – ~5 nm thick – Protein concentration in membrane varies. – Structure of discrete membrane regions influences neuronal function. Copyright © 2016 Wolters Kluwer • All Rights Reserved The Prototypical Neuron—(cont.) • The cytoskeleton – Not static – Internal scaffolding of neuronal membrane – Three structures • Microtubules • Microfilaments • Neurofilaments Copyright © 2016 Wolters Kluwer • All Rights Reserved The Prototypical Neuron—(cont.) • 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 Copyright © 2016 Wolters Kluwer • All Rights Reserved The Prototypical Neuron—(cont.) • 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 Copyright © 2016 Wolters Kluwer • All Rights Reserved The Prototypical Neuron—(cont.) • The synapse – Synaptic transmission – Electrical-to-chemical-toelectrical transformation – Synaptic transmission dysfunction leads to mental disorders. Copyright © 2016 Wolters Kluwer • All Rights Reserved The Prototypical Neuron—(cont.) • Axoplasmic transport – Anterograde (soma to terminal) vs. retrograde (terminal to soma) transport Copyright © 2016 Wolters Kluwer • All Rights Reserved The Prototypical Neuron—(cont.) • Dendrites – “Antennae” of neurons – Dendritic tree – Synapse—receptors – Dendritic spines • Postsynaptic (receives signals from axon terminal) Copyright © 2016 Wolters Kluwer • All Rights Reserved Classifying Neurons • Classification based on number of neurites – Single neurite • Unipolar – Two or more neurites • Bipolar: two • Multipolar: more than two Copyright © 2016 Wolters Kluwer • All Rights Reserved Classifying Neurons—(cont.) • Classification based on dendritic and somatic morphology – Stellate cells (star-shaped) and pyramidal cells (pyramid-shaped) – Spiny or aspinous Copyright © 2016 Wolters Kluwer • All Rights Reserved Classifying Neurons—(cont.) • Classification by connections within the CNS • Primary sensory neurons, motor neurons, interneurons • Classification based on axonal length • Golgi type I • Golgi type II Copyright © 2016 Wolters Kluwer • All Rights Reserved Classifying Neurons—(cont.) • Classification based on gene expression – Creation of transgenic mice • Example of “ChAT-Cre mice” – Green fluorescent protein • Classification based on neurotransmitter type Copyright © 2016 Wolters Kluwer • All Rights Reserved Glia • Function of glia – Support neuronal functions • Astrocytes – Most numerous glia in the brain – Fill spaces between neurons – Influence neurite growth – Regulate chemical content of extracellular space Copyright © 2016 Wolters Kluwer • All Rights Reserved Astrocyte Glia—(cont.) • Myelinating glia – Oligodendroglia (in CNS) – Schwann cells (in PNS) – Insulate axons Cross section of myelinated nerve fibers Copyright © 2016 Wolters Kluwer • All Rights Reserved Glia—(cont.) • Myelinating glia—(cont.) – Oligodendroglial cells – Node of Ranvier • Region where axonal membrane is exposed Copyright © 2016 Wolters Kluwer • All Rights Reserved Other Non-Neuronal Cells • Ependymal cells • Microglia as phagocytes (immune function) • Vasculature Copyright © 2016 Wolters Kluwer • All Rights Reserved Concluding Remarks • Structural characteristics of the neuron provide insight into how neurons and their different parts work. • Structure correlates with function. Copyright © 2016 Wolters Kluwer • All Rights Reserved