Neurotransmission

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Neurotransmission

• Steve Croker / ext 2081 / C009
• s.croker_at_derby.ac.uk

Outline

• Historical context
• Neurons
• Neurotransmission neurotransmitters
• Neural networks

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History

• Previously thought body worked according to
  mechanical/hydraulic principles
• 1791, Galvani-frogs legs-nerves conducted
  electricity
• End of the hydraulic theory
• 1875, Golgi stained individual nerve cells
• Ramon y Cajel-different nerve types-separate

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The Neuron
Fig 1. Dodgy drawing of a neuron
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Parts of The Neuron

• Soma
• contains nucleus and other important material
  that provides for the life processes in the cell
• Dendrites
• receive the messages between neurons
• Axon
• links together the cell body and the terminal
  buttons 
• Terminal buttons
• where the message is passed over to another
  neuron, across the synapse

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Neuronal Transmission

• Communication via chemicals (neurotransmitters)
• Neurotransmitter passed from presynpatic to
  postsynaptic neuron
• Receptor sites are sensitive to a particular
  transmitter
• Excitation / inhibition of postsynaptic neuron
• If threshold is reached, the signal is passed
  along 

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Neurotransmitters

• Classical Neurotransmitters
• Noradrenaline, Dopamine, Serotonin, GABA,
  Achetylcholine, Glutamate
• Neuromodulators
• Modulate the effect of neurotransmitters
• Agonists Antagonists
• Mimic / block effects of neurotransmitters
• Used to treat organic brain disorders

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Resting Potential

• -70mv voltage difference between inside outside
  of cell
• How / why?
• Different ionic concentrations
• Ioncharged atom
• Higher concentration of sodium ions outside cell
  (101)
• Higher concentration of potassium ions inside
  cell (401)

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Action Potential

• Nerve impulse
• Produced when threshold potential (-55mV)
  reached
• Sodium channels open
• Sodium ions enter
• Potential rises to 30mV
• Potassium channels open
• Potassium ions exit
• Potential sinks to 80mV

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Action Potential
Fig 2. clever drawing of an action potential
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Neurotransmitter release

• Action potential travels along axon to terminals
• Synaptic vesicles contain neurotransmitter
• S.V.s fuse with membrane
• Neurotransmitter poured into synaptic gap
• Binds with receptors

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Synapse
Fig 3. Synapse (not real Colours)
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Synaptic Vesicle fusing with Membrane
Fig 4. Slightly blurred vesicle
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Neural Networks

• Also connectionism, PDP
• AI technique
• Analogous to processes in the brain

Fig 5. Units and Connections
If sum of inputs gt threshold, unit is Activated
and signal is propagated
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Example
output units
hidden units
input units
a
b
c
t
Fig 6. Small neural network
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Similarities
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Differences
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Some Concerns

• Choices of representation
• inputs outputs chosen according to domain
• Specific problems
• small scale neworks
• fail to scale up
• Nonlocal effects
• Wide diffusion of chemical over brain

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Learning Outcome

• Fundamental understanding of neuronal
  transmission

Reading

• Wickens, A. (2000). Foundations of biopsychology.
  Harlow Prentice Hall. Ch. 1
• On the web
• Brain Mind magazine
• http//www.cerebromente.org.br/
• neuroscience for kids !
• http//faculty.washington.edu/chudler/introb.html