GENERAL PHYSIOLOGY OF
• Excitation in CNS
• The reflex principle of CNS activity
• General physiology of receptors
Both somatic and autonomic nervous
systems have two divisions:
• Sensory division (for collecting information)
• Motor division (for executing the action)
The nervous system can be divided into two
• 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 tissues
1. Regulation of movement
2. Maintenance of homeostasis
3. Individual adaptation of the organism to the
4. Intelligence and mental activity
Organs and tissues effect of CNS
1. Functional (stimulation or inhibition)
2. Trophic (affect the metabolism of
innervate organs for normal growth and
3. Vasomotor (vasoconstriction and
The principal and specific
manifestation of the activity of the
central nervous system is THE REFLEX
A REFLEX - is a regular
reaction of the organism to a change in
it’s external or internal
environment, effected through the CNS
in response to the stimulation of
• 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 reflex
Classifications of receptors
• By location:
– Internal = interoceptors (visceroceptors,
vestibuloceptors and proprioceptors)
– External = exteroceptors (signal of the outside world )
• By the physical nature of the stimuli:
• By sensitivity:
• By detection of the stimuli:
• By adaptation:
– Rapidly adapting( - fall with time)
– Slowly adapting=non-adapting ( - const)
Functions of receptors
• Detection (present or not?)
• Object-quality discrimination (poor or
• 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 impulses
– pattern of nerve impulses
Mechanism of excitation of the Primary
1. stimulation of receptors' membrane
2. generation of receptors' potential - RP (a local response)
3. elecrotonic propagation of RP to an axon (the same cell)
4. generation of AP
5. AP propagate along afferent nerve 14
Mechanism of excitation of the Secondary receptor.
1. Stimulation of receptors' membrane
2. Generation of receptors' potential - RP (a local
3. Elecrotonic propagation of RP to
presynaptic membrane (the same cell)
4. Release of chemical transmitter to synaptic
5. Activation of postsynaptic membrane –
generating potential (GP - a local response
in another cell)
6. Elecrotonic propagation of GP to an axon
7. Generation of AP
8. AP propagate along afferent nerve
1. Neuronal reception
2. Integration of signals
4. Regulation of effectors
Functions of neuron
Classification of neurons
By number of branches
1. By form
2. By function
(sensory, motor, vegetative, neu
3. By location in NS
4. By location in reflex arc
(afferent, inter-, efferent)
6. By effect
7. By form of activity
(background and silent)
Functions of Glial cells
of CNS and
Classification of synapses
1. By location (axo-
2. By effect (excitatory
3. By basis of process
4. By transmitter
•The activity of a nerve cell can be inhibited
without the participation of special
•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.
Neural center is
group of neurons
acting together in
of a definite reflex
or in regulation of
• 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
performance of one
function or a reflex
and are located in
the certain site of a
Properties of the nervous centers
are caused by structure and function of the synapses
1. One-way conduction.
2. Delayed conduction.
• -Secretion of the mediator
• -Diffusion of the mediator
• -Generation of
3. Summation of excitation.
а). Special summation - the summing of the synaptic
inputs from different neurons upon the dendrites
and cell body of one neuron.
b). Temporal summation - occurs when one
presynaptic neuron can increase its effect on one
postsynaptic neuron by firing repeated.
4. Transformation of rhythm – it’s 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.
6. Long term potenciation (posttetanic
potencyation) - amplification of reflex reaction
after rhythmic and often irritation of the nervous
The reason - accumulation in presynapse calcium ions.
7. Occlusion The phenomenon
occlusion will be, that
the quantity of excited
afferent inputs of both
appears less, than the
arithmetic sum of
excited neurons at
separate irritation of
everyone afferent an
The phenomenon occlusion
results in decrease in force of
expected total response.
inputs cause such
appears more than
the arithmetic sum
of reactions at
The phenomenon of the central simplification is
characterized by opposite effect of occlusion.
• 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
• 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
• diminished sensitivity of the postsynaptic
membrane to the mediator (it is called habituation
or desensitization or accommodation).
10. Fatigue of the nervous centers.
• 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, narc
(ether, chloroform, barbiturates), alcohol, and many
11. High sensitivity surplus C02, lack 02 and
Coordination 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:
1. divergence and convergences
2. feedback connection
3. irradiation excitation
5. reciprocal innervation
7. plasticity of the nervous centers
9. common final way
PRINCIPLES OF COORDINATION IN CNS
Relaying of signals thought neuronal
Divergence and Convergence
Irradiation 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
Principle 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.
motoneurons of muscles
ispiratory and expiratory
neurons the respiratory
center, and other.
Principle 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:
1. At this moment excitability and its liability neurons raises.
2. Intensity of its excitation amplifies even the weakest
irritations because of high ability to sum EPSP.
3. It is very proof, it is difficult for inhibition.
4. It is capable to inhibiting other centers.
5. It is capable to draw to itself excitation of other nervous
Principle of plasticity of the
• 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.
Principle of subordination
•In CNS hierarchical mutual relations take place:
the underlaying department submits
to instructions of an overlying
•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.