Lecture 2: Neurotransmission
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
The Neuron
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
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
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
Resting Potential
- -70mv voltage difference between inside & outside of cell
- How / why?
- Different ionic concentrations
- Ion=charged atom
- Higher concentration of sodium ions outside cell (10:1)
- Higher concentration of potassium ions inside cell (40:1)
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
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
Neural Networks
- Also 'connectionism', 'PDP'
- AI technique
- Analogous to processes in the brain
Similarities
| Neurons | N.Net |
|---|---|
| Neuron | Unit |
| Synapse | Connection |
| Action Potential | Output |
| Analogue input | Analogue input |
| Discrete output | Discrete output |
Differences
| Neurons | N.Net |
|---|---|
| Different neurotransmitters | Ignored |
| Complex calculation of excitation | Simple summation of inputs |
| - | Learning algorithm |
| Large, complex | Small, simple |
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
Learning Outcome
- Fundamental understanding of neuronal transmission
Reading
- Wickens, A. (2000). Foundations of biopsychology. Harlow: Prentice Hall. Ch. 1