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
Dec 19, 2015
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
• 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
• 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 voltage-gated 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
• 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 blood-
brain 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