© 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?