Download Chapter 02: Neurons and Glia

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
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The Neuron Doctrine
• Histology
– Microscopic study of tissue
structure
– Nissl stain
• Facilitates the study of
cytoarchitecture in the
CNS
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The Neuron Doctrine—(cont.)
• Golgi stain (developed by Camillo Golgi) revealed
two parts of neurons:
– Soma and perikaryon
– Neurites: axons and dendrites
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Basic Parts of a Neuron
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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
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Neurites in Contact, Not Continuity
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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)
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The Prototypical Neuron—(cont.)
• The nucleus
– Gene expression
– Transcription
– RNA processing
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Internal Structure of a Typical Neuron
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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
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The Prototypical Neuron—(cont.)
• The soma—(cont.)
– Ribosomes the major site for
protein synthesis
• Rough endoplasmic
reticulum
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The Prototypical Neuron—(cont.)
• The soma—(cont.)
– Protein synthesis also on free ribosomes;
polyribosomes
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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
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The Prototypical Neuron—(cont.)
• The soma—(cont.)
– Mitochondria
• Site of cellular respiration
(inhale and exhale)
• Krebs cycle
• ATP is cell’s energy source.
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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.
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The Prototypical Neuron—(cont.)
• The cytoskeleton
– Not static
– Internal scaffolding of
neuronal membrane
– Three structures
• Microtubules
• Microfilaments
• Neurofilaments
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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
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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
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The Prototypical Neuron—(cont.)
• The synapse
– Synaptic transmission
– Electrical-to-chemical-toelectrical transformation
– Synaptic transmission
dysfunction leads to mental
disorders.
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The Prototypical Neuron—(cont.)
• Axoplasmic transport
– Anterograde (soma to terminal) vs. retrograde
(terminal to soma) transport
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The Prototypical Neuron—(cont.)
• Dendrites
– “Antennae” of neurons
– Dendritic tree
– Synapse—receptors
– Dendritic spines
• Postsynaptic (receives
signals from axon
terminal)
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Classifying Neurons
• Classification based on number
of neurites
– Single neurite
• Unipolar
– Two or more neurites
• Bipolar: two
• Multipolar: more than
two
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Classifying Neurons—(cont.)
• Classification based on
dendritic and somatic
morphology
– Stellate cells (star-shaped)
and pyramidal cells
(pyramid-shaped)
– Spiny or aspinous
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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
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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
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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
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Astrocyte
Glia—(cont.)
• Myelinating glia
– Oligodendroglia (in CNS)
– Schwann cells (in PNS)
– Insulate axons
Cross section of
myelinated nerve fibers
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Glia—(cont.)
• Myelinating glia—(cont.)
– Oligodendroglial
cells
– Node of Ranvier
• Region where
axonal membrane
is exposed
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Other Non-Neuronal Cells
• Ependymal cells
• Microglia as phagocytes (immune function)
• Vasculature
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Concluding Remarks
• Structural characteristics of the neuron provide
insight into how neurons and their different parts
work.
• Structure correlates with function.
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