Habituation & Sensitisation

Habituation & Sensitisation

1. Learning in Aplysia

   • Habituation of gill withdrawal reflex
     • After many touches the response declines. No change in rate of firing of sensory neuron. No change in responsivity of motor neuron, if directly stimulated. No fatigue of muscle but decrease in release of transmitter (reduced EPSP) from sensory cell

2. Sensitization

   • Temporarily increased response to siphon touch when noxious stimulus is applied to tail
     • This was due to increased release of serotonin at 2 synaptic sites. Both in the sensory neuron and facilitating neuron

3. Long-term sensitization

   • due to structural changes in the pre-synaptic terminals e.g., sensory neuron 1
     • up to 2-fold increase in number of synaptic terminals in both sensory and motor neurons.

4. Long-term habituation linked with 1/3 reduction in number of synaptic terminals.