Information Processing in Sensory Neuron
You have previously seen that the sensory neuron transmits the information it receives, as an action potential along its axon. We describe them an impulse. The intensity of the stimulus is transmitted along the nerve fibre through changing frequency. A stimulus of greater intensity will result in greater frequency of firing along the axon, one of lower intensity will comprise lower frequency. Let us see what happens when one of the first pair of legs of a cockroach is touched. Stimulation of the mechanoreceptors of the first leg of a cockroach by touch will be perform by the axon to neurons in the first thoracic ganglion where it makes connection, in simplest case, through synapse, along with a motor neuron directly. In more complicated cases, the motor neuron may be informed by one or more association neurons. These neurons may be receiving at similar time a number of other stimuli from a large number of presynaptic fibres. Some of them might be excitatory and some of them may be inhibitory, So carrying opposing instructions.
This type of connection also enables higher centers of the central nervous system to exert control over the action, so that, if unsuitable, it can withhold from exercising the reflex, like running away. Thus the postsynaptic cell receiving frequently contradictory messages, decides whether to fire or not, on the basis of all the instructions it receives. In case the neuron 'decides' to fire, the stimulus can result in the release of neurotransmitter at its terminals making the concerned muscle to contract, causing movement of the leg and the animal run away. This type of receptor-effector loop is the lowest level of information processing via central nervous system and is called a reflex. In lower animals this constitutes their whole behavior. However, in higher animals particularly in those like cephalopods and insects, with a well developed central nervous system, varying degrees of higher levels of control are exerted on the reflexes along with increasing hierarchy of the central nervous system exerting its influence. These animals comprise larger and complex type of brains by invertebrate standards; their large eyes and other sense organs feed a range of stimuli into the brain. There are various motor centres in the central nervous system finally controlling activities through various motor centres. We must not forget that most animals have as well the capacity of learning. Learning provides the animal with a record of information on which it can draw and act. The memory gives this information and the central nervous system can select the motor activity best suited for the animal's life.