Brain
Behavioural responses and complexity of life
In the above SENSATION-ACTION CIRCUIT, there is almost no processing of information, the STIMULUS / SENSATION results into a instantaneous single RESPONSE/ACTION. That’s the reason such actions, that do not involve analytical thinking, are termed as KNEE-JERK RESPONSE.
Single-SYNAPSE responses are very characteristic of lower organisms like insects, reptiles, fishes and lower mammals. As the animals evolve, the number of SYNAPSES and connections increase allowing more flexibility in response and analytic capabilities.