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© Kip Smith, 2003
Psychology 110B
Introduction to Neurons
The stuff of the brain and mind
© Kip Smith, 2003
Cerebral cortex 4 lobes 2 hemispheres
Motor area Sensory areas Association areas
Review Nervous system
Central Spinal cord Brain
• Cortex, etc Peripheral
Sensory Motor
• Autonomic• Skeletal
© Kip Smith, 2003
Review
Perception & cognition
Connects the hemispheres
Limbic system Drives Memory Emotion
Sensory relay station
Rapid motion Life support &
homeostasis
© Kip Smith, 2003
Functionaldifferentiation Cortical regions with
specialized functions
Motion
Speech production
Modulation of emotion
Speech comprehension
Hearing
Vision
Topographic organization
© Kip Smith, 2003
Hemispheric asymmetry of ‘higher’ functions
Left Language
Broca’s area Wernicke’s area
Putting it all together
Right Visuospatial Faces Maps
© Kip Smith, 2003
Neuroimaging
Goal: discover, identify, and take pictures of the regions of the brain that are actively supporting mind and behavior
The underlying assumption Active neurons require nourishment Blood oxygen, hemoglobin, sugars, etc. More activity, more bloodflow
Measure bloodflow, infer neural activity
© Kip Smith, 2003
PETPositron Emission Tomography
Radioisotopic tracer injected into bloodstream Oxygen 15 decays to Nitrogen + a positron
Half-life 80 seconds Positron annihilates an electron Reaction generates 2 gamma rays travelling in
opposite directions
© Kip Smith, 2003
Patterns of gamma ray emissions locate where isotope decayed
Density of decay is proportional to bloodflow More bloodflow is inferred to reveal more
neural activity
PETPositron Emission Tomography
Neuroimages using PET
© Kip Smith, 2003
fMRI Functional Magnetic Resonance Imagery
A strong external magnet polarizes iron ions in hemoglobin
The polarized ions create a secondary, induced magnetic fieldand radio wavesat characteristicfrequencies
© Kip Smith, 2003
Neurons
The elementary units of the information processing system
Integrate and transmit pulses of electrical charge
Are linked by chemical neurotransmitters
© Kip Smith, 2003
Soma (cell body)
Axon
Myelin sheath
Dendrites
Terminal Buttons
A neuron & its parts
© Kip Smith, 2003
Neural communication
Neurons form chains and networks through which they send packets of information
© Kip Smith, 2003
Neural communication
Neurons form chains and networks through which they send packets of information
© Kip Smith, 2003
Neural communication
Neurons form chains and networks through which they send packets of information
© Kip Smith, 2003
Neural communication
Neurons form chains and networks through which they send packets of information
© Kip Smith, 2003
Key terms in neural communication
Terminal button Neurotransmitters Synapse Dendrite Soma, cell body Axon Myelin
Excitatory connection Inhibitory connection Activation level Threshold Repolarization Action potential Depolarization Spreading activation Plasticity
© Kip Smith, 2003
Graded chemical communication
Soma
Terminal ButtonDendrite
Synapse
Neurotransmitters
© Kip Smith, 2003
Hundreds of neurons release chemical neurotransmitters that adhere to the dendrites of a target neuron
Glutamate Acetylcholine Dopamine Serotonin Norepinephrine ...
Neurotransmitters
© Kip Smith, 2003
Excitatory connections increase the rate of firing of the target neuron
Excitatory connections
© Kip Smith, 2003
Inhibitory connections decrease the rate of firing of the target neuron
Inhibitory connections
© Kip Smith, 2003
Chemical communication between neurons at the synapse becomes electrical communication within the neuron
Axon
MyelinSoma
© Kip Smith, 2003
The target neuron accumulates these packets of information
The accumulation is called its activation level
The threshold is its limited capacity for information
Activation & Threshold
© Kip Smith, 2003
When the amount of information reaches its threshold, (i.e, when it ‘fills up’ with information),
it becomes fully (re)polarized
and generates an action potential, a brief quantum of electrical charge that travels down its axon to its terminal buttons
Repolarization
© Kip Smith, 2003
The charge travels down the axon to the terminal buttons
Action potential
The action potential is a quantum (an all-or-nothing unit ) of electric charge
© Kip Smith, 2003
the action potential travels down the axon to the terminal buttons.
Depolarization
The cell body depolarizes when
© Kip Smith, 2003
From electrical communication within the neuron to chemical communication at the synapse
When the action potential reaches the terminal buttons, they release chemical neurotransmitters across the synapse with the the next target neuron
Information flows from one neuron to the next
© Kip Smith, 2003
Neural communication
The transmission of information is known as spreading activation
© Kip Smith, 2003
The brain is a neuronal information processing system
Billions of neurons that are arrayed in networks & energized by spreading activation
The neural networks form specialized regions with
Topographic organization Highly precise interconnections Localization of function
© Kip Smith, 2003
Neuronal plasticity
Learning causes neurons to develop new neurons and more terminal buttons and to make more synaptic connections
This plasticity Is most rapid in young children Is most evident in the hippocampus Declines with age
© Kip Smith, 2003
Summary
Information is represented in patterns of spreading activation across interconnected networks of neurons
Localization of function: Different parts of the brain contain networks of
neurons that process different types and sources of information and direct different behaviors
Limbic system => Emotion Frontal cortex => Reason, judgment
© Kip Smith, 2003
The brain is the most complex thing we know about
Normal behavior requires all the parts to work together
Multiple patterns of spreading neural activation must interact seamlessly
It usually works. Sometimes it doesn't:
© Kip Smith, 2003
Psychoactive drugs
Either enhance or block synaptic transmission Three mechanisms
© Kip Smith, 2003
At the terminal button
Either facilitate the release of the neurotransmitter Speed, cocaine
Or inhibit the release of the neurotransmitter Antipsychotics
© Kip Smith, 2003
Within the synapse
Either facilitate the reuptake of the neurotransmitter
Or inhibit the reuptake of the neurotransmitter Clinical antidepressants, Zoloft (?)
© Kip Smith, 2003
At the dendrite
Either block access Caffeine (blocks inhibitory connections)
Or act like a neurotransmitter LSD, psilocybin,nicotine, Valium (increases inhibitory connections)
© Kip Smith, 2003
Questions?
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