Download Lecture 2: Structure and function of the NS

Introduction to
Computational
Neuroscience
Lecture 2: Structure and function of the NS
lunes, 5 de septiembre de 16
Lesson
Title
1
Introduction
2
Structure and Function of the NS
3
Windows to the Brain
4
Data analysis
5
Single neuron models
6
Network models
7
Artificial neural networks
8
Artificial intelligence
9
Learning and memory
10
Perception
11
Attention & decision making
12
Brain-Computer interface
13
Neuroscience and society
14
Future and outlook
15
Projects presentations
16
Projects presentations
lunes, 5 de septiembre de 16
Basics
Analyses
Models
Cognitive
Applications
Physiology
Anatomy
Function
Structure
Clinical
Computational
Information
processing
Cognitive
Behavioral
Cellular, Molecular, Developmental, Evolutionary,...
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“One of the difficulties in
understanding the brain is that it is
like nothing so much as a lump of
porridge”
R.L. Gregory
Eye and the Brain: the psychology of seeing,
New York, 1966, McGraw-Hill
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“What I cannot create,
I don’t understand”
R. Feynman
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Where mental faculties sit?
vs.
Hippocrates
Ancient Egypt
Plato
Aristotle
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Galen
What are the building blocks?
1906 Nobel Prize in Medicine or Physiology
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Learning objectives
• Cell types (neurons and glial cells)
• Methods of communication (synapses)
• Organization of the NS (the basic plan)
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Introduction to the NS
Gross anatomy of the CNS
Neuronal signaling
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Most animals have a nervous system that
allows responses to stimuli
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Evolution of the NS
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Evolution of the NS
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Evolution of the NS
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Division of the vertebrate NS
2
The nervous system has central
and peripheral parts:
The Human Brain
CNS
PNS
Central Nervous System (CNS)
* Brain
* Spinal cord
Peripheral Nervous System (PNS)
Nerves outside the brain and spinal cord
* Cranial nerves
* Spinal nerves
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Figure 1–1 Central and peripheral nervous systems. The
Division of the vertebrate NS
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Division of the CNS
CHAPTER 1
Cerebral
hemisphere
Diencephalon
The brain itself
has multiple
subdivisions:
Brainstem
Introduction to the Nervou
Cerebellum
Spinal cord
Cerebrum
Diencephalon
Cerebellum
Brainstem
Brain stem
Cerebellum
A
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B
C
Division of the PNS
Sensory division
Picks up sensory information and delivers it to the CNS
Motor division
Carries information to muscles and glands
* Divisions of the Motor division
* Somatic carries information to skeletal muscle
* Autonomous carries information to smooth muscle,
cardiac muscle, and glands
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Function of the NS
CNS and PNS must work in harmony to carry
3 main functions
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Function of the NS
CNS and PNS must work in harmony to carry
3 main functions
1 Receive sensory input
Monitor changes occurring inside and outside the
body (changes = stimuli)
* Sensory receptors gather information
* Information is carried to the CNS
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Function of the NS
CNS and PNS must work in harmony to carry
3 main functions
2 Perform integration
To process and interpret sensory input and decide
if action is needed
Sensory information is used to create
* Sensations
* Memory
* Thoughts
* Decisions
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Function of the NS
CNS and PNS must work in harmony to carry
3 main functions
3 Generate motor output
A response to integrated stimuli is given
* Decisions are acted upon
* Impulses are carried to effectors (muscles or glands)
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Cellular elements
2 cell categories in the
nervous system:
Neurons (information
processing, signaling
elements, 100 billion)
Glial cells (supporting
roles, 10 x neurons)
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Neurons: compartments
Brainstem
Cerebellum
Spinal cord
Diencephalon
Brainstem
Neurons have specialized zones for collecting, integrating,
conducting, and transmitting information.
Cerebellum
A
B
C
Figure 1–2 Three-dimensional reconstruction of the entire CNS, seen from the left side (A), from directly in front (C), and from halfway in between
(B). The eyes are included with the reconstruction because, as described in Chapter 2, the retina develops as an outgrowth from the neural tube.
Soma supports metabolic
and synthetic needs
Dendrite
Dendrites receive
information from other
neurons via synapses
Axon conducts information
away from cell body
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Synapse
Axon
Figure 1–3 Schematic view of a typical neuron, indicating synaptic inputs to its dendrites (although other sites are possible) and information flow
down its axon, reaching synaptic endings on other neurons. Information flow is unidirectional due to molecular specializations of various parts o
neurons, as described in Chapters 7 and 8. The pink segments covering the axon represent the myelin sheath that coats many axons (see Figs. 1-24
and 1-30), and the gap in the axon represents a missing extent that might be as long as a meter in the longest axons.
Neurons: synaptic contacts
22
Figure 1–20 Potential sites of synaptic contacts. Most synapses consist
of an axon terminal contacting a dendrite and are therefore called axodendritic (AD) synapses. However, all other possible combinations occur
at least occasionally, giving rise to two-part names indicating the presynaptic and postsynaptic elements. These include axosomatic (AS) synapses, dendrodendritic (DD) synapses, and axoaxonic synapses with the
postsynaptic element being another axon terminal (AA1) or the initial
segment of an axon (AA2). (Based on an illustration in Pannese E: Neurocytology: fine structure of neurons, nerve processes, and neuroglial cells,
New York, 1994, Thieme Medical Publishers.)
21
Chemical
(neurotransmitters)
AA2
DD
AA1
AD
AS
CHAPTER 1
Electrical
AD
Introduction to the Nervous System
Synapse: axonal end abupts on other neuron
(dendrites). A few thousand per cell
2 to 20 nm space (Cajal vs Golgi)
1 µm long where the axon is separated from extracellular
space only by fingerlike projections from Schwann cells.
The myelin between two nodes is an internode and is
formed by a single Schwann cell (Fig. 1-24); adjacent
internodes form the projections that cover the node
The Human Brain
Electrical
A
Figure 1–21 Synapses densely distributed over the surface of CNS neu
campal neuron developing in tissue culture. The cell body (not seen in
directed against MAP2, a microtubule-associated protein restricted to the
originating from other neurons not visible in this field form a dense netw
directed against synaptotagmin, an integral membrane protein of synap
axon terminal is superimposed on part of the dendrite, appears yellow.) B
of a rat), stained for MAP2 as in A, showing neuronal cell bodies and den
the cell bodies and dendrites, were stained with a fluorescent antibody d
terminals (red fluorescence). A third dye (DAPI) was used to stain the nucle
and Pietro De Camilli, Yale University School of Medicine. B, from the cover p
nf
D
*
*
At
*
m
Computational advantages
Table 1–2
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Components of the Peripheral Nervous S
Cell or Cell Part
Type
Neuronal cell bodies
Sensory neurons
Neurons: diversity
CHAPTER 1
Neurons come in a variety of
sizes and shapes, but all are
variations of the same theme
Introduction to the Nervous System
C
5
(Actual size)
B
A
Cell bodies range from
5 to 100 micras in diameter
Most axons around 1 mm
but some 1 m
D
F
G
E
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Figure 1–4 Examples of multipolar (A to E), bipolar (F), and unipolar (G) neurons, all drawn to about the same scale to demonstrate the range of
neuronal sizes and shapes. All were stained by the Golgi method (see Fig. 1-14A); dendrites are indicated by green arrows, axons by blue arrows. A,
Purkinje cell from the cerebellar cortex. B, Granule cell from the cerebellar cortex. C, Projection neuron from the inferior olivary nucleus. D, Spinal cord
Neurons: functional types
Sensory neurons take nerve impulses from sensory receptors to
CNS
Sensory receptors may be the end of a sensory neuron itself (a
pain or touch receptor), or may be a specialized cell that forms a
synapse with a sensory neuron
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Neurons: functional
Interneurons occur entirely within the CNS
Convey nerve impulses between various parts of the CNS
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Neurons: functional
Motor neurons carry nerve impulses from CNS to muscles or
glands
Have many dendrites and a single axon
Cause muscle to contract or glands to secrete
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Neurons: segregation
CHAPTER 1 Introduction to the Nervous System
9
Neuronal Cell Bodies Synthesize
Macromolecules
Neuronal cell bodies and axons are largely segregated within
the CNS
The neuronal cell body is the site of synthesis of nearly
all the neuron’s enzymes, structural proteins, membrane
components, and organelles, as well as some of its
chemical messengers. Its structure (Fig. 1-9) reflects this
function. The nucleus is large and pale-staining, with
most of its chromatin dispersed and available for transcription; it contains one or more prominent nucleoli,
which are actively involved in the transcription of ribosomal RNA. The cytoplasm contains abundant rough
endoplasmic reticulum and free ribosomes for protein
synthesis, together with stacks of Golgi cisternae for
further processing and packaging of synthesized proteins. Many mitochondria are also present to meet the
energy requirements of continuous, very active protein
synthesis.
Ribosomes, whether studding the surface of the rough
endoplasmic reticulum or free in the cytoplasm between
the cisternae, are stained intensely by basic dyes, appearing by light microscopy as clumps called Nissl bodies or
Nissl substance (Fig. 1-10). Nissl bodies are particularly
prominent in large neurons, a consequence of the large
total volume of cytoplasm contained in their processes,
Grey matter: cell bodies and
dendrites (pinkish due to blood
supply)
Figure 1–7 Horizontal slice of a whole human brain, approximately
6 mm thick, stained by a method that differentiates between gray and
white matter. Pretreatment with phenol makes the white matter resistant to the blue copper sulfate stain, so white matter appears white and
gray matter appears bright blue. (Prepared by Pamela Eller, University of
Colorado Health Sciences Center.)
White matter: axons (myelin)
DRG
From sensory receptors
AG
To viscera
To skeletal muscle
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Figure
1–8 Division ofde
the 16
CNS into gray matter and white matter, as typified by the thoracic spinal cord in cross section. Gray matter contains
de
septiembre
Glial cells (PNS)
Schwann cell
nucleus
c
Glia = glue in Greek
Unrolled
internode
Ol
c
c
Schwann cells:
* Form myelin sheath in the PNS
* Speed up axonal transmission
nf
AxM
Axon
A
Myelin
Schwann cell:
nucleus cytoplasm
Axon
Ol
B
Ol
Satellite cells:
* Support clusters of neuron
bodies (ganglia)
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AxM
m
nf
Figure 1–28 CNS myelin sheaths, here in a transverse section of a rat’s optic nerve. Each axon contains microtubules (m) and neurofilaments (nf)
F
s
m
w
f
t
a
b
n
(
S
Glial cells (CNS)
Microglia
Oligodendrocytes
* Dispose of debris
* Respond to injury
* Form myelin sheaths
Astrocytes
Ependymal
* Mop up excess ions
* Connect neurons to
blood vessels (Bloodbrain barrier)
* Scar tissue
* Line ventricles
* Secrete CSF
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Neurons vs. Glial cells
Glial cells (astrocytes) could be involved in processing
The vast majority of neurons do not divide. Why?
Glial cells divide
Most brain tumors are gliomas
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Introduction to the Nervous System
Gross anatomy of the CNS
Neuronal signaling
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Figure 3–3 A, Average brain weights of human males and females at different ages. Notice how the brain grows rapidly after birth, doubling in the
first year of life, before reaching its full size at about age 11 years. At all ages, male brains have a greater average weight than female brains. However,
as indicated in B, adult female brains actually account for a greater percentage of body weight than do adult male brains. Brain growth is substantial
in utero, and we are born with brains that are very large relative to body size. After the brain growth spurt of the first 1 to 3 years of life, body growth
takes over, and the brain weight–body weight ratio declines progressively until about age 17. (Plotted from data in Dekaban AS, Sadowsky D: Ann Neurol
4:345, 1978.)
Gross anatomy
Opossum
Rabbit
Kangaroo
CHAPTER 3
Humans have large brains
relative to other animals (1.1 to 1.7 kg)
1.2
0.9
0.6
0.3
0 .5 1
2
Chimpanzee
Lion
Elephant
Gross5 Anatomy
and General Organization
of the Central Nervous
cm
Male
0.0
Cat
Brain (kg)/Body (kg)
Brain weight (kg)
A
Human
Figure 3–4 Brains of a series of representative mammals, all reproduced at the same scale. Brain size is partly related to body size (e.g., cat versus
lion, human versus elephant) and partly related to mental abilities (e.g., lion versus human). Not all parts of the brain change size in proportion to one
another. For example, the olfactory bulbs of opossums and coyotes (blue arrows) are relatively large, those of monkeys and chimpanzees (green arrows)
are proportionally much smaller, and those of humans are barely discernible at this magnification. (From www.brainmuseum.org, courtesy Dr. Wally
Welker; supported by NSF grant 0131028.)
Female
1.5
Rhesus
monkey
Coyote
3 4.5 6.5 8.5 11 14 17 20 26 35 45 53
Age (years)
More complex interconnections and
selective expansions of cerebral cortex
involved in higher functions
B
0.15
0.12
Fem
0.09
Mal
0.06
0.03
0.00
0 .5 1
2
3 4.5 6.5 8.5 11 14 17 20
Age (years)
Figure 3–3 A, Average brain weights
of human males and females at different ages. Notice how the brain grows rapidly after b
Figure 3–5 The relative sizes of
brainat
of about
a rhinoceros
first year of life, before reaching its fullthesize
ageand11 years. At all ages, male brains have a greater average weight than fem
alleged brain of the author.
as indicated in B, adult female brainsthe
actually
account
for a greater percentage of body weight than do adult male brains. Brain g
Although
the rhino’s
body weight
about 30
times
greater,
its brain
in utero, and we are born with brainsisthat
are
very
large
relative to body size. After the brain growth spurt of the first 1 to 3 years
weight is likely to be only half as
takes over, and the brain weight–bodygreat.
weight
progressively until about age 17. (Plotted from data in Dekaban AS, Sado
(Rhino, ratio
courtesydeclines
Albrecht
Dürer. Author, courtesy Mr. and
4:345, 1978.)
Mrs. Nolte. Suggested by an illustration in Cobb S: Arch Neurol
12:555, 1965.)
Opossum
400 gr at birth
1400 gr adult (due to increase in
myelin and new connections)
50-80k neurons die every day
Coyote
Rabbit
Rhesus
monkey
Human
Cat
Kangaroo
Lion
5 cm
Chimpanzee
Elephant
Figure 3–4 Brains of a series of representative mammals, all reproduced at the same scale. Brain size is partly related to body
lion, human versus elephant) and partly related to mental abilities (e.g., lion versus human). Not all parts of the brain change size i
another. For example, the olfactory bulbs of opossums and coyotes (blue arrows) are relatively large, those of monkeys and chimpa
are proportionally much smaller, and those of humans are barely discernible at this magnification. (From www.brainmuseum.or
Welker; supported by NSF grant 0131028.)
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Frontal lobe (9)
Gross anatomy
(motor cortex)
Parietal lobe (10)
(somatosensory cortex)
14
15
16
Overview of the
subdivisions of the
CNS
Cerebral
cortex
7
Occipital lobe (11)
(visual cortex)
8
Temporal lobe (12)
6
(auditory cortex)
Limbic lobe (13)
(drives, emotions, memory)
Caudate nucleus (14)
Basal
ganglia
7
5
Cerebral
hemisphere
Lenticular nucleus
(movement control;
related structures
in brainstem)
(putamen [15]
and globus pallidus [16])
Hippocampus (5),
amygdala (6)
(limbic structures;
drives, emotions, memory)
Cerebrum
Thalamus (7)
(relay to cortex)
Diencephalon
Brain
Cerebellum (1)
(coordination)
Midbrain (2)
Brainstem
Central
nervous
system
Hypothalamus (8)
(control of autonomics)
Pons (3)
Medulla (4)
9
10
13
7
8
11
2
3
12
Spinal
cord
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1
4
1
Figure 3–25 Overview of the subdivisions of the CNS. The major structures listed here, as well as many related structures, are the subjects of subse-
Gross anatomy
Cerebral hemispheres are folded and convoluted
* Gyri: bumps
* Sulci: grooves
Corpus callosum is a huge bundle of axons connecting
the two hemispheres (severed in split-brain patients)
Ventricles filled with cerebro-spinal fluid that bath the brain
and provide protection and chemical environment of neurons
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Gross anatomy
Cerebral cortex: outermost 6 layered structure of the neural
tissue of human and other mammals (2-4 mm). Key role in
high cognitive functions (memory, attention, language, ...)
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Gross anatomy
CNS contains systematic distorted maps
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Introduction to the Nervous System
Gross anatomy of the CNS
Neuronal signaling
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Neuronal signaling
Within the neuron (conduction)
To achieve long distance (several cm), rapid communication (150
m/s), neurons have evolved special abilities for sending electrical
signals (Action potentials)
Between neurons (transmission)
Communication between neurons is achieved at synapses
by the process of neurotransmission
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Electrical properties
Lipid bilayer at the cell surface acts as a
capacitor (able to store charges)
Neurons spend a lot of energy to keep
different concentration of ions inside and
outside (resting membrane potential -70
mV)
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Electrical properties
Neuron membranes are filled with pores that enable the selective
pass of ions (ion channels)
Ion channels open and close as a
function of the membrane potential
(voltage-gated channels)
Diffusion: when channels open ions tend
to move to less crowded places
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Conduction: Action
http://www.youtube.com/watch?v=7EyhsOewnH4
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Conduction: Action potential
An action potential is conducted whenever an input of threshold
intensity or above is applied to the initial part of an axon (each
action potential has the same strength)
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Conduction: Action potential
Saltatory conduction: action
potential jumps between nodes but
needs to be regenerated
Speed up of transmission
* unmyelinated 5 m/s
* myelinated 150 m/s
(toe - spine in < 7 ms)
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quickly to the original resting potential. B, Injection of little more than half
action potentials. At the termination of the current pulse the membrane stay
potentials continue at a slower rate. C, Replacing the Cl− in the solution bath
it to behave like a myotonic fiber. (From Adrian RH, Bryant SH: J Physiol 240:
Conduction: Action potential
Figure 7–19 A puff
York, 1851, Rudolph G
Puffer fish (fugu) contains a potent poison that blocks Na+
channels resulting in failure to generate action potentials
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Neuronal signaling
Within the neuron (conduction)
To achieve long distance (several cm), rapid communication (150
m/s), neurons have evolved special abilities for sending electrical
signals (Action potentials)
Between neurons (transmission)
Communication between neurons is achieved at synapses
by the process of neurotransmission
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Synaptic transmission
Electrical synapses: gap junctions between cells that allow ions to
flow from one neuron to another (also in cardiac cells)
Chemical synapses: most neurons communicate by means of
neurotransmitters at chemical synapses. The receiving neuron
THE POST
responds with a graded potential that may or may not initiate7.2an
action potential
Reserve
vesicles
RRVP Transmitter
Recycling
Action
potential
Release
machinery
Postsynaptic
receptors
PSC
[Ca 2+]
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which, on release, may activate a corresponding pool of postsynaptic receptors (Walmsley et al., 1998). The RRVP is replenished from a large reserve
Fig
che
exa
con
con
repl
poo
pote
thro
cha
vesi
the
rele
Synaptic transmission
1 Action potential arrives to the axon
terminal (pre-synaptic neuron) stimulates
the release of packets of neurotransmitters
into the synaptic cleft
2 Neurotransmitters diffuse across the
synaptic cleft
3 Neurotransmitters bind to receptors at
the post-synaptic neuron causing ion
channels to open
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Synaptic transmission
http://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/sites/dl/free/
0072437316/120107/anim0015.swf::Chemical%20Synapse
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Synaptic transmission
EPSP
IPSP
Depending on which receptor is activated at the post-synaptic
neuron the electrical response can be excitatory or inhibitory
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Synaptic transmission
Neural integration refers to the conduction and addition of all PSP
produced by various excitatory and inhibitory synapses. It
determines if an action potential is generated. Two types:
1 Temporal summation
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Synaptic transmission
Neural integration refers to the conduction and addition of all PSP
produced by various excitatory and inhibitory synapses. It
determines if an action potential is generated. Two types:
2 Spatial summation
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Synaptic transmission
Synaptic strength can be enhanced or depressed by changing
neurotransmitter release or the density of receptors (synaptic
plasticity)
Drugs, diseases, and toxins interfere with synaptic
neurotransmission (alcohol, nicotine, marihuana, antidepressants,
botox,...)
too much botox...
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Summary
•
•
NS evolved to provide a fast and coordinated response to stimuli.
•
Neurons have specialized compartments to receive (dendrites),
integrate (soma), conduct (axon), and transmit (synapses)
impulses.
•
NS is divided in CNS (brain and spinal cord) and PSN (cranial and
spinal nerves), with further subdivisions involved in specialized
processing.
2 types of cells: neurons (information processing) and glial cells
(supporting role).
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To know more
http://cnx.org/content/m47519/latest/?
collection=col11569/latest
Chapters 1 and 3
The human brain: an introduction of its functional
anatomy, John Nolte,
Mosby, 2002
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Lesson
Title
1
Introduction
2
Structure and Function of the NS
3
Windows to the Brain
4
Data analysis
5
Single neuron models
6
Network models
7
Artificial neural networks
8
Artificial intelligence
9
Learning and memory
10
Perception
11
Attention & decision making
12
Brain-Computer interface
13
Neuroscience and society
14
Future and outlook
15
Projects presentations
16
Projects presentations
lunes, 5 de septiembre de 16
Basics
Analyses
Models
Cognitive
Applications