Transcript Lecture 2 Powerpoint file

Class Web Site
• Go to www.uleth.ca ->current students > class websites -> NEUR 3680A >Class Website
• You will find the course outline as well
as lecture slides there
Reading associated with
upcoming lectures
• Read chapter 1 for historical overview
• Today’s lecture comes from chapter 2 use the lecture to guide your reading,
this chapter is in much more detail than
you need for this course
• We will discuss techniques, especially
neuroimaging, which is found in
chapters 3 and 4
Goals and Methods
What is the goal of Cognitive
Neuroscience?
Goals and Methods
• Broad goal is to understand how the brain
accomplishes cognitive processes such as
attention, memory, language and
consciousness
Goals and Methods
• But there are some smaller steps that
we need to take:
– HOW: how do neurons work (physiology)
and how do they interact to form circuits?
– WHERE: for a given cognitive task, where
are the neurons that do that job
Structure of Neurons
• The Neuron Doctrine
– brain was originally thought to be one
continuous mesh of connected soma
(Camillio Golgi)
– Modern view: Brain is composed of
discrete cells (Santiago Ramon y Cajal)
Structure of Neurons
– Basic parts of the neuron
– Cell Body contains DNA, manufactures
proteins, energy, “decides” whether to send
signal to next neuron
Structure of Neurons
– Basic parts of the neuron
– Dendrites receive input from other
neurons, transmit “passive” potential to cell
body
Structure of Neurons
– Basic parts of the neuron
– Axon conducts signal from cell body to
other neurons
Neurons are electrically active
• Membrane dynamically swaps charges
(ions)
• At “rest” positive charges accumulate on
outside, negative on the inside…how?
Neurons are electrically active
• Selective permeability plus Na+/K+
pump
Neurons are electrically active
• If a neuron must use ATP to maintain its
charge, what does it mean for the brain
to be “active” or “inactive”?
Neurons are electrically active
• Two kinds of membrane potentials:
graded potential vs. action potential
Neurons are electrically active
• Graded potential
– stimulation (usually a post-synaptic potential) causes Na+ to
enter the cell, depolarizing the membrane
– Na+ disperses along membrane, spreading depolarization
that decreases in strength with distance
Neurons are electrically active
• Importance of Graded Potential
– graded potentials “sum” to determine if
neuron will transmit signal (analog
computation)
Neurons are electrically active
• Importance of
Graded Potential
– Electroencephalography
(EEG) measures graded
potentials
– depolarization at one end
of cell body leads to
extracellular currents that
can be measured on the
scalp!
Neurons are electrically active
• Action Potential occurs when voltagegated channels open
Neurons are electrically active
• Action Potential occurs when voltagegated channels open
• Voltage-Gated channels are clustered
where axon and cell body meet (axon
hillock) and along the axon
Neurons are electrically active
• Opening of voltage-gated channels triggers
an “active” propagation of depolarization
along the length of the axon
Neurons are electrically active
• Importance of the Action Potential
– AP “spikes” can be measured with electrodes
placed beside the cell - a powerful tool in
measuring neural responses to various stimuli
Neurons are electrically active
• Importance of the Action Potential
– Action Potential is “all-or-nothing” (digital
computation)
The synapse and
neurotransmitters
• Signals “jump” from one neuron to
another at the synapse
The synapse and
neurotransmitters
• Arrival of AP triggers influx of Calcium
ions
• Neurotransmitter is released and
diffuses across cleft
• Receptor molecules on post-synaptic
side allow Na+ to enter
The synapse and
neurotransmitters
• Importance of the synapse and
neurotransmitters
– neurotransmitters have different functions and are
associated with specific circuits in the brain
– e.g. dopamine has a role in learning and in
addiction; norepinephrine plays a role in attention
The synapse and
neurotransmitters
• Importance of the synapse and
neurotransmitters
– The synapse is the site of action of most
psychoactive drugs
– e.g. stimulants (e.g. cocaine, amphetamine) act on
dopamine, depressants (e.g. alcohol) act on
GABA
The synapse and
neurotransmitters
• Importance of the synapse and
neurotransmitters
– Brain can “reprogram” itself by adjusting the
efficacy of synapses - important difference
between brains and (current) computers
The synapse and
neurotransmitters
• Gap Junctions are direct electrical
connections between neurons
– thought to be faster than normal synapses
– some connections in the retina are gap junctions
The Role of Glia
• Glia outnumber neurons 10 to 1 !
• Believed to perform “support” roles
– guidance during development
– “plumbing” and maintaining the bloodbrain barrier (fMRI)
– mylination
• More recently thought to play a
direct role in cognitive function
– glia have electrically active membranes
– may enter into electrical circuits with
neurons via gap junctions