The work of the nervous system based on the principle of reflex, that is in a certain way it responds to external and internal stimuli. Reflex – is an adequate response to the stimulus of the body, carried out through the nervous system. In the implementation of reflex reaction excitement spreads reflex arc. The structure of the reflex arc includes receptor perceiving irritation. Often, the receptor is the peripheral endings of sensory (afferent) nerve. In the axon of sensory neurons excitation gets into the central nervous system and is distributed or directly on the motor (efferent) neuron, or intercalary neurons, and after them – on the efferent. As axon efferent neuronal excitation reaches of the executive body, often the muscles. As a result, the excitation operation of this body varies: for example, the muscle contracts.
Reflexes are divided into somatic ending contraction of skeletal muscles, and autonomic, which resulted in changing the work of internal organs. An example of the simplest somatic reflex arc can serve as a knee-jerk, consisting of only two neurons: sensory and motor (afferent and efferent) – and does not contain neurons.
Reflexes have a number of common features. They can be disassembled for example cough reflex.
If a person has mild irritant receptors touches the pharynx, the first unpleasant sensations arise. Gradually, however, the central nervous system occurs summation, and there is a response reflex reaction of the body – cough.
Reflex properties of the so-called local sign – ie a place of stimulation and determines the place of the reflex reaction. For example, during stimulation of receptors occurs precisely cough pharynx instead twitching limbs.
The stronger the stimulus, the shorter the time reflex. Power reflex reaction also depends on the strength of stimulation. With slight irritation coughing weak, but strong inflammation in cough involved not only the muscles of the pharynx, but also the muscles of the chest, abdominals, diaphragm and even limbs.
If the intensity of stimulation is low and does not increase with time, it can develop addictive, that is, the weakening of cough. If the strength of stimulation, conversely, is high, the contrast may develop addiction sensitization, i.e. increased sensitivity to stimuli. For example, with severe pain in the throat, not only develops a cough, but it would seem that a sore neck, ears and teeth.