Inhibiting in cns

Russian physiologist Ivan Sechenov discovered central inhibiting – chemical irritation of thalamus inhibits simple spine non-conditioned reactions. He was the first who underlined that inhibiting is active process. Inhibiting has been considered only as passive process coming after overexcitement before Sechenov.

Inhibiting (inhibition) is a special nervous process expressed externally in answer reaction weakening or complete disappearance. It is characterized by definite intensiveness and duration. Inhibition is an innate process which is improved in course of human onthogenesis.

Primary – it is not connected with excitement process and occurs with inhibitory cells (Ranshow cells) participation.

Secondary – appears without inhibitory neurons. It is nervous system overexcitement result.

Postsynaptic – EPSP formation. It is urgent but particular one.

Presynaptic or protective - it is developed the mostly often in axo-axonal synapses in brain stem and spine. Essence: presynaptic membrane hyperpolarization. Mediator – glycine. It protects from pathological, excessive, unnecessary information. It is non-urgent but more complete comparatively to the previous one.

Pessimal - It is central inhibition type. It appears at irritation high frequency. High rate of answer excitement occurs at first moment. Then stimulated central neuron comes in inhibiting state while working in such a regimen.

Recurrent – it is primary inhibition example. Essence: neuron activity inhibiting caused by recurrent axon collateral of this neuron.

Reciprocal –It belongs to postsynaptic inhibiting. This inhibiting can be belonged to nervous center co-ordination principles (see materials of next lesson). Expiration and inspiration centers are inhibited reciprocally in medulla oblongata, pressor and depressor cardiac-vascular centers. It is rather distinct at spine level at highly co-ordinated acts performance (walking, running, scretching et al.). At spinal segments the excitement of motoneurons causing muscles-flexors contraction is accompanied by reciprocal inhibiting of other motoneurons group leading to extensors relaxation. So, shortly, flexors excitement and parallel extensors inhibiting (and on the contrary) occurs. There are two explanation of spinal reciprocal inhibiting:

• impulses multiplication mechanism is switched on on the way from afferent fiber to muscle extensor motoneurons at muscle flexor motoneurons excitement; as a result – extensors motoneurons are receiving highly-rated impulsation leading to their pessimum state – so, inhibiting;

• inhibitory associative neurons synthesizing inhibitory mediator are switched on on the way to extensors motoneurons.

Lateral – activity neurons or receptors located near to excited neurons or receptors are interrupted. Lateral inhibiting mechanism provides sensory systems discriminative ability. So, it provides sounds rate determining in auditory sensory system; in visual one – increases significantly contrast of percepted image; in tactile one – encourages differentiating 2 points of touching. Lateral inhibiting is connected significantly with recurrent inhibiting mechanisms. It is also postsynaptic inhibiting.