Read Chapter 02: Neurons and Glia text version

Neuroscience: Exploring the Brain, 3e

Bear Neurons and Glia Lecture 2

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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

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The Neuron Doctrine

· Histology ­ Study of tissue structure ­ The Nissl Stain · Stains RER in cell body and dendrites · Facilitates the study of cytoarchitecture in the CNS

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Neurons

The fundamental neural circuit element Neurons come in many Shapes and sizes

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The Neuron Doctrine

· Golgi-stain (Developed by Camillo Golgi) shows two parts of neurons: ­ Soma and perikaryon (interchangeable) · The cell body of a neuron, containing the nucleus and organelles. · [peri- + Greek karuon, nut] ­ Neurites: Axons and dendrites

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Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins

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

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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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Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins

Cell Body Peroxisomes

Membrane Pore Lysosomes

Contain Hydrolases The Recycling Garbage Person

Golgi Apparatus

Plasmologen Production

Rough Endoplamic Reticulum (RER) Smooth Endoplamic Reticulum (SER)

Cell Nucleus

Vesicles The Protein Plan

Mitochondrion Plasma Membrane, Lipid Bilayer Centrosomes Microtubule organizing Actin Filaments

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Clathrin coated vesicles

Microtubules

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Nuclear Pores

Site of transport (passive and active) through nuclear plasma membrane. Made up of 100 nucleoporin proteins to form the combined active and passive channel

Nucleoplasm

Gel like filler Unknown composition

Heterochromatin

Coiled Mass Involved in gene silencing

Nucleolus

Site of rRNA and ribosome production. Assembled ribosomes are transported to RER through nuclear pores where with mRNA protein transcription takes place

Euchromatin

10 nM Microfibrils

Chromatin DNA + Histone Bodies + RNA and Proteins

The Nucleus

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The Prototypical Neuron

· The Nucleus ­ Gene expression ­ Transcription ­ RNA processing

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What are Genes?

Genes are sequences of coding (exon) and non coding (intron) nucleotide triplets. Exon triplets define the amino acid sequence in a protein.

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What are bases and nucleotides ?

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How are Base Sequences Held Together?

Nucleotides are joined by Phosphodiester bonds into the Coded gene sequence. Note for future reference the 3' End and the 5' Ends.

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Exon triplets define the amino acid sequence in a protein Involves Complementary Base Pairing

Double And Triple Weak Molecular Bonds (Hydrogen Bonds)

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Sequences of Complementary Base Pairs form the Double Helix of DNA Which Contains the Gene Codes for Proteins

Phosphodiester bonds and their phosphates (in green) define the alpha helix. Bases face inside the molecule aligned as complementary base pairs (bp). The helix must be unzipped to read the base sequence codes.

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Sequences of Complementary Base Pairs form the Double Helix of DNA Which Contains the Gene Codes for Proteins

Bases face inside the molecule aligned as complementary base pairs (bp). The helix must be unzipped to read the base sequence codes. As an example DNA replication

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Codes for Proteins Are Read by the production of Messenger RNA (mRNA) by RNA Polymerase in the Nucleus

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Codes for Proteins Not all of the code in mRNA translatable into proteins. Translatable code is in exons, non protein codes are introns

Intron coding sequences of mRNA may be edited out by post translational modification

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The Prototypical Neuron

· The Nucleus ­ Gene expression ­ Transcription ­ RNA processing

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Codes for Proteins Are "read" by the production of Messenger RNA (mRNA) by RNA polymerase in the Nucleus. mRNA travels out through nuclear pores to RER (rough endoplasmic reticulum) studded with ribosomes, protein complexes with enzymes that read the triplet complement codes and guide transfer RNA (tRNA) which carry amino acids corresponding to the code into place.

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DNA Transcription ­ a Colorful Reminder

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The Prototypical Neuron

· The Soma ­ Major site for protein synthesis · Rough endoplasmic reticulum

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The Prototypical Neuron

· The Soma ­ Protein synthesis also on free ribosomes; polyribosomes

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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

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The Prototypical Neuron

· The Soma ­ Mitochondrion · Site of cellular respiration (inhale and exhale) · Krebs cycle · ATP- cell's energy source

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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

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The Prototypical Neuron

· The Cytoskeleton ­ Not static ­ Internal scaffolding of neuronal membrane ­ Three "bones" · Microtubules · Microfilaments · Neurofilaments

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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

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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

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The Prototypical Neuron

· The Axon ­ Synapse · Synaptic transmission · Electrical-to-chemical-toelectrical transformation · Synaptic transmission dysfunction · Mental disorders

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The Prototypical Neuron

· The Axon ­ Axoplasmic transport ­ Anterograde (soma to terminal) vs. Retrograde (terminal to soma) transport

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The Prototypical Neuron

· 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 the Number of Neurites ­ Single neurite · Unipolar ­ Two or more neurites · Bipolar- two · Multipolar- more than two

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Neurons

The fundamental neural circuit element Neurons come in many Shapes and sizes

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Classifying Neurons

· Classification Based on Dendritic and Somatic Morphologies ­ Stellate cells (star-shaped) and pyramidal cells (pyramid-shaped) ­ Spiny or aspinous

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Copyright © 2007 Wolters Kluwer Health | Lippincott Williams & Wilkins

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

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Information flow in neuronal circuits is into dendrites

and then to the soma . and then through axons to synapses

and onto the next cell

Therefore Information flow is directional. How this happens is now explanable at the molecular level and is one of the issues we will address

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The Neuron Doctrine

Cajal's Contribution

­ Neural circuitry ­ Neurons communicate by contact, not continuity

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The patella reflex

A simple human neural circuit

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The Patella Reflex

A simple human neural circuit

Transduction of information to the neural language of electrochemical communication

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Glial Cells

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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

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Glia

· Myelinating Glia ­ Oligodendroglia (in CNS) ­ Schwann cells (in PNS) ­ Insulate axons

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Glia

· Myelinating Glia (Cont'd) ­ Oligodendroglial cells ­ Node of Ranvier · Region where the axonal membrane is exposed

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Glia

· Other Non-Neuronal Cells ­ Microglia as phagocytes (immune)

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Information

Chapter 02: Neurons and Glia

49 pages

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