Sensitivity is the ability of the body to perceive external and internal stimuli, to analyze and subsequently provide an adequate response.
I. P. Pavlov’s theory of analyzers laid the foundations for understanding the nature and mechanisms of sensitivity.
From the point of view of phylogenetic development, there are following types of sensitivity:
- protopathic;
- epicritical.
Protopathic sensitivity is more ancient; it has limited opportunities to differentiate stimuli by their modality, intensity and localization.
Epicritical sensitivity is a phylogenetically new function to perform quantitative and qualitative assessment of stimuli by modality, intensity and localization.
In general, sensitivity is classified to:
- superficial (exteroceptive);
- deep (proprioceptive);
- complex forms (two-dimensional spatial sense, discriminative sensitivity, stereognosis);
- interoceptive (visceroceptive).
Superficial (exteroceptive) sensitivity is defined by sensations formed in sensitive skin structures or mucous membranes in response to external factors or environmental changes. These sensory modalities are also called superficial, or skin, coming from the mucous membranes.
There are three types of exteroceptive sensitivity:
- pain;
- temperature (cold and heat);
- touch (feeling of a light touch).
Pain sensitivity (nociception) is used to warn about potentially dangerous stimuli. Tactile sensations (touch) — thanks to this sensory modality, we recognize the three-dimensional features of the environment. The temperature sensitivity is aimed to determine the temperature.
Deep (proprioceptive) sensitivity includes myoesthesis, vibration, feeling of pressure, body weight. Proprioceptive sensitivity comes from deep tissues, i.e., muscles, ligaments, tendons, joints and is aimed to monitor the position of the body in space and the movement of the joints.
Complex sensory modalities include pinprick sensation, touch sense, recognition of signs and letters written on the skin (two-dimensional spatial sense), distinguishing of simultaneous pricks in two close points with a Weber’s caliper (discriminative sensitivity), and stereognosis. The term “complex sensitivity” is used to describe those sensory modalities, which require a cortical component to finalize perception. At the same time, the leading function is considered to be perception and discrimination as compared to a simple sensation in response to stimulation of the primary sensory endings. The stereognosis refers to ability to perceive and understand the shape and nature of objects by touching and feeling.
Interoceptive sensitivity, also called visceroception, is a sensation caused by irritation of the receptors of internal organs. Visceroception is aimed to perceive features of body’s internal enviroment (heart abnormalities, lack of oxygen).
Sensory information, or input, is partially realized, since basically it acts as the basis for many regulatory processes that occur unconsciously: proprioception and touch for motor coordination, thermoception for automatic temperature regulation, changes in breathing for fluctuations of the blood gas content, pain stimuli for trigger protective reactions, etc.
Sensitive analyzers consist of the following:
- peripheral (receptor) division;
- conduction pathway;
- cortical division.