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GENERAL PHYSIOLOGY OF CENTRAL NERVOUS SYSTEMExcitation in CNSThe reflex principle of CNS activityGeneral physiology of receptors

Both somatic and autonomic nervous systems have two divisions:Sensory division (for collecting information)Motor division (for executing the action)2The nervous system can be divided into two main parts: Somatic (skeletal muscles) Autonomic (visceral organs and vessels)

The main function of the nervous system is integration of the activity of all systems, organs and tissuesIt provide: Regulation of movementMaintenance of homeostasisIndividual adaptation of the organism to the external environmentIntelligence and mental activity3

Organs and tissues effect of CNSFunctional (stimulation or inhibition)Trophic (affect the metabolism of innervate organs for normal growth and development)Vasomotor (vasoconstriction and vasodilatation)4

The principal and specific manifestation of the activity of the central nervous system is THE REFLEXA REFLEX - is a regular reaction of the organism to a change in its external or internal environment, effected through the CNS in response to the stimulation of receptors5

Reflex arcs include:ReceptorAfferent neuronInterneuronEfferent neuronEffector

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In a simple reflex arc there are two neurons and just one synapse. Such reflexes are therefore known as monosynaptic reflexes.

Other reflex arcs have one or more neurons interposed between the afferent and efferent neurons. These neurons are called interneurons

If there is one interneuron, the reflex arc will have two synaptic relays and the reflex is called a disynaptic reflex7

Reflex rings include:ReceptorAfferent neuronInterneuronEfferent neuronEffectorFeedback

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Classifications of receptorsBy location:Internal = interoceptors (visceroceptors, vestibuloceptors and proprioceptors)External = exteroceptors (signal of the outside world )9 By the physical nature of the stimuli:-phonoreceptors-photoreceptors-mechanoreceptors-thermoreceptors-chemoreceptors-baroreceptors

10By sensitivity:High-sensitiveLow-sensitiveBy detection of the stimuli:Mono-modalPoly-modalBy adaptation:Rapidly adapting( - fall with time) Slowly adapting=non-adapting ( - const)

By mechanism of activation:

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Functions of receptors

Detection (present or not?)

Object-quality discrimination (poor or strong?)

Sensory transduction (The process of transforming some property of the external or internal environment into nerve impulses)

Coding of stimulus intensity and duration frequency of nerve impulsespattern of nerve impulses12

Adaptation and coding13

Mechanism of excitation of the Primary receptorstimulation of receptors' membranegeneration of receptors' potential - RP (a local response) elecrotonic propagation of RP to an axon (the same cell)generation of APAP propagate along afferent nerve14

15Mechanism of excitation of the Secondary receptor.Stimulation of receptors' membraneGeneration of receptors' potential - RP (a local response)

Elecrotonic propagation of RP to presynaptic membrane (the same cell)Release of chemical transmitter to synaptic cleftActivation of postsynaptic membrane generating potential (GP - a local response in another cell)Elecrotonic propagation of GP to an axon Generation of APAP propagate along afferent nerve16

Structure of neuron17

1. Neuronal reception (receive information)2. Integration of signals (excitation end inhibition)3. Conduction 4. Regulation of effectors5. Trophic6. Neurosecretory7. Memory

18Functions of neuron

Classification of neuronsBy number of branches

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1. By form2. By function (sensory, motor, vegetative, neurosecrethory)3.By location in NS4.By location in reflex arc (afferent, inter-, efferent)6. By effect (excitatory, inhibitory)7.By form of activity (background and silent)

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Functions of Glial cellsIon buffer(astrocite)Intake neurotransmittersIsolation (olygodenrocyte, Schwanny-cells)Protective (microglia)BasicTrophicTransportRegeneration of CNS and ontogenesis

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Classification of synapses1. By location (axo-somatyc, axo-dendrityc, axo-axonic)2. By effect (excitatory and inhibitory)3. By basis of process (electrical, chemical and electro-chemical)4. By transmitter22

Groups of neurotransmitters(by chemical building)Esters (acetylcholine)Monoamines (norepinephrine, dopamine, serotonin)Amino acids (GABA (-Aminobutyric acid), glutamate)Purines (adenosine, ATP) Peptides (enkephalins, substance P, VIP)Inorganic gases (NO)

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Electrical (a) and chemical (b) synapses24

ab

Excitatory postsynaptic potentials (EPSP)

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Inhibitory postsynaptic potential (IPSP)

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Inhibition in CNS it's active process, witch result is easing of excitation or its termination. Functions of inhibition:-Coordination-Protection

Inhibition is always consequence of excitation.

Inhibition in CNSInhibition following excitationPessimalPresynapticReciprocal Recurrent LateralDirect

Primary

Secondary

Postsynaptic

Primary Inhibitions Presynaptic

Postsynaptic Direct

IPSPEPSP

RecurrentLateralReciprocalPrimary Inhibitions

Secondary Inhibitions

Inhibition following excitation Pessimal (st > max)

Secondary Inhibitions

The activity of a nerve cell can be inhibited without the participation of special inhibitory structures.

Pessimal inhibition develops in the excitatory synapses as a result of strong depolarization of the postsynaptic membrane under the influence of nerve impulses arriving too frequently.

Inhibition following excitation - a discrete type of inhibition is that developing in a nerve cell after termination of excitation and which appears when excitation is followed by strong after-hyperpolarization of the cell membrane.

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Neural center is group of neurons acting together in the performance of a definite reflex or in regulation of a particular function.

The nervous center in the broad sense of the word - groups of neurons, laying on the different floors CNS and incorporated not morphologically, but it is functionally for regulation of any strictly certain function. The nervous center in the narrow sense of the word - group of neurons that are incorporated for performance of one function or a reflex and are located in the certain site of a brain.

Properties of the nervous centersare caused by structure and function of the synapses One-way conduction.

Delayed conduction. (0,3-0,8 ms) -Secretion of the mediator -Diffusion of the mediator -Generation of postsynaptic potential

Summation of excitation. ). Special summation - the summing of the synaptic inputs from different neurons upon the dendrites and cell body of one neuron. 37

b). Temporal summation - occurs when one presynaptic neuron can increase its effect on one postsynaptic neuron by firing repeated.

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Transformation of rhythm its change of action potentials frequency after their passage through synapse or neural center.

Biological sense of transformation is: 1) amplification of the important signal for an organism; 2) reduction of a insignificant signal for an organism; 3) the coordinated activity of two different neurons in a reflex arch.

5. Reflex after-action - continuation of reflex after termination of afferent stimulation.

After-depolarization of neuronsReverberatory circuit Long-term postsynaptic potential

6. Long term potenciation (posttetanic potencyation) - amplification of reflex reaction after rhythmic and often irritation of the nervous center.

The reason - accumulation in presynapse calcium ions.

7. Occlusion

The phenomenon occlusion will be, that the quantity of excited neurons at simultaneous irritation afferent inputs of both nervous centers appears less, than the arithmetic sum of excited neurons at separate irritation of everyone afferent an input separately. The phenomenon occlusion results in decrease in force of expected total response.EPEP

8. Simplification

EPSP+ EPSP=APEPSPEPSPThe simultaneous irritation afferent inputs cause such response that appears more than the arithmetic sum of reactions at separate irritation afferent inputs.The phenomenon of the central simplification is characterized by opposite effect of occlusion.

44 The afferent impulses from peripheral;

Various humoral stimulants (hormones, C02, etc.);

The are impulses continuously sent from nerve centers to the periphery maintain the tone of the skeletal muscles and of the smooth muscles of the intestine, and vascular tone.9. Reflex tone - constant excitation of the nerve centers.

45 The fatigue of the nervous centers is connected to fatigue of interneuronal synapses.

The reasons of fatigue is:

Sharp fall in the reserves of synthesized mediator in the nerve ending, reduction in synapse of energy reserve (such as ATP), diminished sensitivity of the postsynaptic membrane to the mediator (it is called habituation or desensitization or accommodation). 10. Fatigue of the nervous centers.

46 The cortical cells of the hemispheres are especially badly damaged by a cessation of blood supply; within as little as 5 or 6 minutes they undergo irreversible changes and die.

Nerve cells and synapses possess a selective sensitivity to certain poisons, which are therefore known as nerve poisons (strychnine, morphine, amphetamine, beptazol, narcotic drugs (ether, chloroform, barbiturates), alcohol, and many others). 11. High sensitivity surplus C02, lack 02 and poisons.

47Coordination is an association of all actions of organism in a single whole, association neurons in the uniform functional ensemble deciding specific target.

Allocate the following principles of coordination:divergence and convergencesfeedback connectionirradiation excitationInductionreciprocal innervationdominantsplasticity of the nervous centerssubordinationscommon final wayPRINCIPLES OF COORDINATION IN CNS

Relaying of signals thought neuronal pools. Divergence and Convergence

Receptor;Afferent neuron;Interneuron;Efferent neuron;Effector.Feedback

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50Irradiation of excitation.

At strong and long irritation of the nervous center the pulses acting in CNS, raise not only the given reflex center, but also other centers.

Irradiation is suppressed inhibitory neurons.

They interfere to irradiation of excitation and provide hit of impulses in strictly certain nervous center.

51Principle of an induction.

These are contrast changes of excitability of the nervous center.

If in the nervous center inhibition develops after excitation is a negative consecutive induction.

If excitation develops after inhibition cause a positive consecutive induction.

Reciprocal innervations.Examples: antagonistic mutual relations between motoneurons of muscles flexor and extensor, between ispiratory and expiratory neurons the respiratory center, and other.

53Principle of a dominant.

The dominant center refers to temporarily prevailing nervous center of hypererethism in CNS. The dominant center subordinates to itself all work of a brain and inhibits other centers.

It possesses a next of properties:At this moment excitability and its liability neurons raises.Intensity of its excitation amplifies even the weakest irritations because of high ability to sum EPSP.It is very proof, it is difficult for inhibition.It is capable to inhibiting other centers.It is capable to draw to itself excitation of other nervous centers.

54Principle of plasticity of the nervous centers At damage of the separate centers of a brain their function can pass to other structures of a brain.

Process of compensation of the lost functions is carried out at obligatory participation of a hemisphere.

55Principle of subordination(cephalisation)

In CNS hierarchical mutual relations take place: the underlaying department submits to instructions of an overlying department.

Evolution of nervous system has consisted in moving function of regulation from underlaying in again educated overlying departments of CNS.It is refers to cephalisation.

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