Facial-mandibular region receptors

Nowadays term “analizator” has been changed in the term “sensor system”. Sensor system is an integrity of peripheral (receptive) and central structures of different levels the management of which is realized by means of direct and indirect connections.

Classification:

1. According to information character coming into CNS from peripheral structures:

• gustatory;

• temperature;

• tactile;

• nociceptive;

• proprioceptive.

2. On functioning specificity:

1. Somato-sensor:

• tactile;

• temperature;

• nociceptive.

2. Chemoreceptors:

• gustatory.

C. Proprioreceptors.

Lingual receptors investigations demonstrated that tactile receptors gives answer reactions first, temperature – second. The latest ones are chemoreceptors.

I.P.Pavlov called all receptors of oral cavity “oral analizator”.

PROPERTIES OF RECEPTORS

1. Specificity of response - each type of receptor gives response to its own specific sensation. Stimulation of pain receptors produces pain sensation. Similarly, stimulation of touch receptors produces touch sensation. Synonym: adequacy or monomodality. Receptors order (from maximum to minimum):

• distant exteroreceptors;

• contact exteroreceptors;

• proprioreceptors;

• interoreceptors do not possess because these receptors must not react to specific stimuli but must act to any stimuli coming inside organism.

2. Polymodality is opposite to specificity. It means possibility to act to all stimuli.

Receptors order (from maximum to minimum):

• interoreceptors;

• proprioreceptors;

• contact exteroreceptors;

• distant exteroreceptors (they do not have).

3. Adaptation or desensitization - when a receptor is continuously stimulated with the same strength of stimulus, after sometime the receptor stops sending impulses through the afferent nerve. Depending upon this property, the receptors are divided into two types:

a) phasic receptors, which get adapted rapidly - touch and pressure receptors;

b) tonic receptors, which are adapted slowly – muscle spindle, pain receptors and cold receptors.

Maximal adaptation have exteroreceptors (more expressed – contact ones: first touching or kiss, clothes; then – distant – phono- and photoreceptors).

4. Response to increase in the strength of stimulus - during stimulation of a receptor, if response given by receptor is to be doubled, strength of stimulus must be increased 100 times. This phenomenon is called Weber-Fechner law, which states that the change in response of a receptor is directly proportional to logarithmic increase in the intensity of stimulus.

5. Electrical property - ability to generate receptor potential and generator potential.

When a receptor is stimulated, a nonpropagated transmembrane potential difference is developed. This is called receptor potential. Receptor potential is not action potential. It is similar to excitatory postsynaptic potential (EPSP) in synapse, endplate potential in neuro-muscular junction and electro-tonic potential in the nerve fiber.

Receptor potential has such important properties.

a) It is non-propagated (local).

b) It does not work according to the law “everything or nothing”.

Receptor potential is receptor cell membrane depolarization (in complex receptor) or free nervous fiber (in simple receptor) at irritator action to the receptor. Receptor potential is local one. It coincides generator potential in simple receptor. But it differs from it in complex receptor. Generator potential is depolarization of free nervous fiber membrane at mediator portion action. Mediator releasing is caused by receptor formation generation. Generator potential is an action potential. It is equal to action potential and works according to law “everything or nothing” (receptor potential undergoes law of force correlation).