NSCI 201 Chapter Notes - Chapter 1: White Matter, Schwann Cell, Microglia

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11 Feb 2014
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Chapter 1 - Studying the Nervous System!
!
Overview!
Neuroscience encompasses how the nervous system is organized, how they develop and how they generate behaviour!
Genetics, genomics, molecular and cell biology, anatomy, systems physiology, behavioural observation and psychology help us find
answers!
Sensory systems tell the organism about its own state and the state of its environment!
Motor systems deal with movement!
Associational systems link the sensory and motor systems, and provide higher order functions like: perception, attention, cognition,
emotions, language, thinking!
!
Genetics, Genomics, and the Brain!
The brain is the product of gene expression!
A gene is both:!
the coding DNA sequences (exons) => the template for mRNA that will eventually be translated into protein!
the regulatory DNA sequences (promoters and introns) => control whether and in what quantities that gene is expressed in a
given cell type
Genomics: a field that focuses on the analysis of complete DNA sequences (coding and regulatory)!
The human genome contains approx. 20,000 genes!
14,000 genes are expressed in the developing and/or mature brain!
8,000 of these are in all cells and tissues!
Lots of brain-specific genetic info is in introns and regulatory sequences!
The diversity and complexity of brain function is due to the varying level and location of genes expressed in specific regions!
Studying the genome helped us realize that some pathologies are due to the mutation of one or a few genes!
e.g. a mutation in a gene that regulates mitosis can = microcephaly!
!
Box 1A - Model Organisms in Neuroscience!
The human brain is hard to study, so we turn to other organisms!
We pick model species based on their assumed enhanced functional capacity (e.g. cats were studied since they are highly visual
animals)!
Studies on invertebrates (e.g. squids and Aplysia californica) gave us information about synaptic transmission, synaptic plasticity, and
the cell biology of neurons!
They have very large nerve cells so were easy to study!
Four model organisms have been chosen based on our ability to do genetic analysis and manipulation on them:!
Caenorhabditis elegans (C. elegans, a nematode) - 19,000 genes
Drosophila melanogaster (fruit fly) - 15,000 genes
Danio rerio (zebrafish) - 24,000 genes
Mus musculus (mouse) - 25,000 genes!
A majority of the genes in the above animals' genomes are expressed in their developing and adult brains!
Advantages: we can do sophisticated genetic manipulations on them because we know a lot about their genomes!
Once we identify a gene for brain development, we can manipulate it in the model organisms !
Studying mutants of these animals allows to identify genes that change their phenotype!
Introducing genes into the genome or deleting (knocking out genes) makes transgenic animals,
Homologous recombination: allows DNA constructs that disrupt or alter the expression of specific genes to be inserted into the
location of the normal gene in the host species!
Crayfish, lobster and insects have been useful for finding basic rules for neural circuit function!
Avians and amphibians are useful for studying neural development!
Mammals are useful for neuropharmacological and behavioural studies on the adult brain!
!
The Cellular Components of the Nervous System!
Golgi thought there was one continuous nerve cell network => the "reticular theory"!
He identified the Golgi apparatus and developed the Golgi stain technique!
The neuron doctrine, discovered by Cajal, overcame the reticular theory!
Neurons are discrete entities!
They communicate through synapses (coined by Sherrington)!
Some neurons communicate through gap junctions, which allow for direct electrical and chemical signals between cells!
The cells of the nervous system are divided into 2 categories:!
Nerve cells (neurons)!
Specialized for electrical signalling over long distances!
Glial cells (neuroglia or glia)!
Support electrical signals!
Repair damaged neurons, act as stem cells in some regions (promote regrowth of damaged neurons)!
Can prevent the regeneration of neurons in some areas!
Both have:!
endoplasmic reticulum, Golgi apparatus, mitochondria, vesicular structures!
specialized fibrillar or tubular proteins that make up the cytoskeleton!
Neuron-specific organelle traits:!
concentrated mitochondria at synapses!
endoplasmic reticulum are not found at axons and dendrites!
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