Open Questions: Neurobiology
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See also: High-level brain organization,
Neurochemistry
Introduction
The basic units of the human central nervous system, as with the rest of
the body, are cells. There are about 200 different types of cells in the
body as a whole, but only two main types in the nervous system:
neurons and glia. Estimates of the numbers of neurons in
the brain are around 50 to 100 billion
(5×1010 to
1011). There are about 10 times as many glia.
Although the neurons are at a numerical disadvantage, they are far more
complex than glia and do most of the active work of the nervous system.
Until fairly recently, the importance of glia wasn't well understood,
but now it is recognized that glia
are essential because they provide nutrition and structural
support for neurons, and because they facilitate the all-important
transmission of electrical signal through neurons.
Of course, neurons have been much better known than glia, because of the
much more active role that they play in the operation of the nervous system.
The basic function of any neuron is to transmit electrical signals
throughout the nervous system. Because of the way that neurons are
networked together in complex ways, they are able to perform any
type of computation, much like electronic digital computers. The latter
are also complex networks of units (transistors) which also work
by transmitting electrical signals. Although the organization and logical
operation differ significantly between a brain and a digital computer,
they do have in common the characteristic of performing computations
by the swiitching of electrical signals within a huge network.
A typical neuron consists of three basic parts:
- A cell body, or soma, much like the body of any other type of
cell, that contains the cell nucleus and various other essential
organelles.
- Many dendrites, which are slender, branched
projections from the surface of the cell body.
- A single axon, which is typically a relatively long filamentary
projection from the cell body.
The dendrites are the part of a neuron which receive electrical signals
from other neurons, through a junction to be discussed later, called a
synapse. A single neuron may have up to ten thousand or so
dendrites.
The axon is the part of the neuron which carries an electrical signal
away from the cell body, on to the dendrites of many other neurons.
An axon is always in only one of two states: resting or excited. It is
this binary property which makes neurons similar to the basic functional
units of an electronic computer, which are also either "on" or "off".
In humans, axons can be as long as a meter or so, long enough to reach
from the base of the spine to the toes. Within the brain, axons are
normally much shorter, but may extend several centimeters. This is
still quite long in comparison to an axon's width, which is about
one micron (one ten-thousandth of a centimeter).
Site indexes
-
Open Directory Project: Neurobiology
- Categorized and annotated links. A version of this
list is at
Google, with entries sorted in "page rank" order. May also be
found at
Netscape.
-
Open Directory Project: Neuropsychology
- Categorized and annotated links. A version of this
list is at
Google, with entries sorted in "page rank" order. May also be
found at
Netscape.
-
WWW Virtual Library: Neuroscience
- Extensive categorized and annotated list of links.
-
Internet Neuroscience Resources
- Good list maintained by
Eric H. Chudler.
-
Neuroguide.com: Neurosciences on the Internet
- "A searchable and browsable index of neuroscience resources
available on the Internet: Neurobiology, neurology, neurosurgery,
psychiatry, psychology, cognitive science sites and information
on human neurological diseases."
Maintained by Neil Busis.
-
Yahoo News Full Coverage: Brain Research
- Links to recent news stories from various sources. Also includes
links to sites dealing with brain research.
-
Galaxy: Neuroscience
- Categorized site directory. Entries usually include
descriptive annotations.
-
Galaxy: Neuropsychology
- Categorized site directory. Entries usually include
descriptive annotations.
-
Galaxy: Psychobiology
- Categorized site directory. Entries usually include
descriptive annotations.
More
here.
Sites with general resources
-
New Scientist Special Report on the Human Brain
- Primarily offers links to many news articles from the past
several years of New Scientist magazine. But there are
also other features, including facts and figures, external links,
frequently-asked questions, and a short bibliography.
-
NeuroWiki
- Group-maintained encyclopedia of neuroscience, based on
Wiki software. Still in early stages of development.
-
Eric H. Chudler
- Home page of an associate professor at the University of
Washington, who provides many external links and maintains the
educational site called
Neuroscience for Kids.
-
Neuroscience for Kids
- Although apparently targeted towards students in elementary
and secondary schools, there is a large amount of information
here for a general audience. Useful external links are scattered
throughout many of the topics. Some of the best areas are
Explore the Nervous System,
Internet Neuroscience Resources,
Brain Facts and Figures,
The Neuroscientist Network (questions and answers), and
Neuroscience in the News.
-
Neuroscience@nature.com
- A portal to relevant Nature Publishing Group resouces in the
field of neuroscience.
-
Brain Mechanisms of Pain: Overview
- Several pages dealing with pain, by
Robert C. Coghill. Includes images and movies
created by functional imaging techniques to illustrate brain
activity during the experience of pain.
-
The Blue Brain Project
- Home page of a research project, based at the
Brain Mind Institute,
to build a unified computer model of the brain.
A key component of the project is to simulate the
neocortical column.
The simulation will be performed in collaboration with
IBM Research.
Surveys, overviews, tutorials
-
Category: Neuroscience
- Topic category from
Wikipedia.
-
The Brain from Top to Bottom
- A superb, interactive tutorial on brain structure and
function. Covers most important topics, like memory, emotions,
and the senses. It offers separate discussions on three
different levels: beginner, intermediate, and advanced.
Discussions are also classified in terms of level of
physical organization (social, psychological, neurological,
cellular, and molecular). Each discussion has many internal
cross references to others, as well as external links on each
page.
-
A Brief Introduction to the Brain
- An introduction to neurobiology that covers topics
from neurons to brain structure to the architecture of the
overall nervous system. Most topics are treated only in brief
overview form.
-
Neuroscience
- Complete online textbook, by Dale Purves, George J. Augustine,
David Fitzpatrick, Lawrence C. Katz, Anthony-Samuel LaMantia,
James O. McNamara, and S. Mark Williams.
Index.
Part of the
NCBI Bookshelf.
-
Comparative Mammalian Brain Collections
- "Provides browsers with images and information from one of
the world's largest collection of well-preserved, sectioned
and stained brains of mammals. Viewers can see and download
photographs of brains of over 100 different species of mammals
(including humans)." Discussses a variety of issues in brain
science, such as brain evolution, development, circuitry, and
functions. Has some good
external references.
-
The Anatomical Basis of Mind
- A monograph in ten chapters, by
Ben Best. It covers many
topics, such as basic neuron physiology, nervous system
development, anatomy of the brain, and neurotransmitters. The
intention was to explain "the functioning of mind", but it
provides useful information whether or not it achieves the ultimate
objective. There's a good
references and bibliography section.
-
Cognitive Neuroscience
- A ScienceWeek
"symposium" consisting of excerpts and summaries of
articles from various sources.
-
Are Immune System Molecules Brain-Builders - And Destroyers?
- March 2008 Scientific American article, subtitled
"Researchers stumble across immune proteins that play an
unexpected - and very different - role in the brain."
-
The Forgotten Brain Emerges
- December 2004 Scientific American Mind article, subtitled
"After disregarding them for decades, neuroscientists now say
glial cells may be nearly as important to thinking as neurons
are."
-
The Addicted Brain: Insights from Imaging
- Brief sidebar from a March 2004 Scientific American article:
The Addicted Brain.
-
Ultimate Self-Improvement
- Brief September 2003 Scientific American article about
the discover over the past decade that the brain is more
changeable than had been supposed.
-
All in the Mind
- October 2001 Scientific American News Scan article,
subtitled "Fact or Artifact? The Placebo Effect May Be A Little
Of Both."
-
Young Cells in Old Brains
- Brief September 2001 Scientific American profile of
Elizabeth Gould, who has discovered a great deal about
neurogenesis in adult brains.
-
Study Finds Placebo Effect Is Fake
- May 2001 Scientific American news article about a
review of clinical trials testing for a placebo effect, and
concluding the effect is largely nonexistent.
-
Getting Wired
- June 1999 Scientific American Science and the Citizen
article, subtitled "New observations may show how neurons form
connections."
-
Deconstructing the Mosaic Brain
Tom Curran
The Scientist, August 2011
- Sequencing the DNA of individual neurons is a way to
dissect the genes underlying major neurological and
psychological disorders.
-
Cortical Crosstalk
Jef Akst
The Scientist, November 2009
- Scientists are eavesdropping on the brain's conversations
in search of clues underlying complex behaviors.
-
Scientists Use Genetics to Map and Control Brain Functions
Gero Miesenböck
Scientific American, September 2008
-
- New Brain Cells Go to Work
R. Douglas Fields
Scientific American, August 2007
- Seeking the Neural Code
Miguel A. L. Nicolelis; Sidarta Ribeiro
Scientific American, December 2006
- Learning how rats escape from cats also reveals how a
storm of electrical pulses sweeping across the brain is
translated into information.
- Mirrors in the Mind
Giacomo Rizzolatti; Leonardo Fogassi; Vittorio Gallese
Scientific American, November 2006
-
- Brain, Repair Yourself
Fred H. Gage
Scientific American, September 2003
-
- The Mutable Brain
Marguerite Holloway
Scientific American, September 2003
-
- Rethinking the "Lesser Brain"
James M. Bower; Lawrence M. Parsons
Scientific American, August 2003
-
- Gray Matters
Jessa Netting
Science News, April 7, 2001, pp. 222-223
- The nervous systems conists of cells known as glia, as well as
neurons. Astrocytes are the most common type of glia, and seem to
be necessary for neurons to grow and transmit signals.
[References]
- Climbing Through the Brain
Robert Kunzig
Discover, August 1998, pp. 60-69
- During gestation, fetal neurons migrate from the central
position in which they develop out towards their final location
in cortex.
- The Attentive Brain
Stephen Grossberg
American Scientist, September-October 1995, pp. 438-449
- The author has been developing a computational approach,
called Adaptive Resonance Theory, to model how the brain matches
sensory inputs with learned expectations. This theory may help
explain perception, learning, and the recognition of information.
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Copyright © 2002 by Charles Daney, All Rights Reserved