Nervous system

The main regulation mechanism of organism's functions

QuestionsNeuron

The reflex arc

The nervous centers

Properties of the nervous centers

The general principles of coordination

Inhibition in the CNS

Spinal cord

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Classification according to a structure and

function:

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Nervous system

Grey matter White matter

Neuron bodies Processes of nervous cells

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Neuron is structural and a functional

unit of nervous system

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Classification of neurons:

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Classification of

neurons by function

neurons

Sensory (afferent) neurons

transmit impulses from skin and other

sensory organs or from various places of the

body to the CNS

Contact (intercalary,association) neurons

providecommunication

between neurons.

Motor (efferent) neurons

transmit impulses from the

CNS to effectors (muscles or glands)

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Perception of external and internal stimuli, the

organization of corresponding adaptive reactions.

The nervous system provides the behavior organization.

Nervous system integrates and monitors the countless

actions occurring simultaneously throughout the entire

human body.

NS is a material basis of mental activity. There are

speech, thinking, consciousness.

Functions of the nervous system

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Reflex arch

Simple

Monosynaptic

Complex

Polysynaptic

(with contact neurons)

Reflex - the basic form nervous activity. Theanswer of an organism to a boring ofreceptors with the assistance of a CNS.

A reflex arc is the neural pathway thatmediates a reflex action.

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Reflex arch consists of 5 main parts

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1. The receptor perceives a irritation,

transforms energy of a irritation into energy

of nervous impulse.

The receptor

exteroreceptors interoreceptors proprioreceptors

senses by which we perceive

the outside world(receptors of a skin, eye,

ear, nasal cavity, etc.)

senses, by which weperceive the pain and movement

of internal organs(receptors of vessels,

internal organs)

react to change of body parts

positionin space

(receptors of muscles,

ligaments, tendons)

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2.An afferent a nervous way - processesof receptor neurons which transfer theinformation to the nervous center.

3.The reflex (nervous) center (is locatedin the CNS) - group of neurons, whichtransfer nervous impulses from afferentto efferent nervous way

4.An efferent a nervous way – transferthe information to an effektor.

5. An effektor – organ, which can answerthe impulses. The impulse causeschanges of its activity .

The nervous center is:

Anatomic definition: the anatomic

clump of the neurons are located in

certain department of a CNS.

Physiological definition: functional

association of the several (anatomic)

centers are located at different levels

of a CNS, which provide difficult

reflex acts (digestion, breathing, etc.)

The nervous centers

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Properties of the nervous centers depend on

mechanisms of conduction of excitation in synapses

1. One-sited conduction of excitation. It is transferring ofimpulse from receptor neuron to effector. It is caused bypresence of synaptic transfer of excitation where it is possibleonly in one site (from presynaptic to a postsynaptic membrane).

2. The delay of conduction of excitation – it is caused bypresence of a considerable quantity of synapses, mediatorreleasing, diffusion through synaptic cleft. Excitation of apostsynaptic membrane demands time – it is called “synapticdelay"

3. Summation of excitation (subliminal stimulus are summated):

summation in time - numerous irritation of receptor by subliminal stimulus causes a reflex.

spatial summation - irritation of receptors of reflex zones by

subliminal stimulus at the same time.

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4. Transformation of rhythm excitation – capacity of

nervous center exchange rhythm of impulses, that transfer from

afferent ways;

5. Afteraction of excitation – circulation of impulses on

chains of nervous center;

6. Fatigue of nervous center – efficiency decreasing, this is

due to disorder of synaptic transmission, attrition of mediator`s

pull and depression of receptors sensitivity to a mediator

(adaptation);

7. The tonus of the nervous centers – is supported by an

afteraction of excitation by afferent impulses, humoral influences

8. Plasticity of the nervous centers – ability to change

characteristic function for them (dysfunction of brain's parts are

provided by other centers)

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The general principles of coordinationFunction of organism

Coordination - interaction of nervous processes in the CNS,referred on association (integration) of organs` functionsand systems.

1. Morphological principles depend on features of a structure of nervous system

2. Functional principles depend on functions of nervous system

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Divergence principle –

neurons are capable to

form numerous synaptic

communications with other

neurons from which there

is a redistribution of

impulses.

Morphological principles

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Convergence

principle – concentration

of excitation from different

neurons to one.

Morphological principles

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Principle of the

general final way -

afferent fibers

converge on the same

intercalary efferent

neurons.

Feedback principle –

control of accuracy of

impellent reflexes.

Morphological principles

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1.Irradiation of excitation (diffusion) –

long strong excitation causes excitation

of many nervous centers.

2.Concentration of excitation.

3.Induction – excitation of the certain

nervous center leads to opposite process

– inhibition of the center bound to it.

Functional principles

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Dominant principle – separated strong excited

center inhibits all other centers.

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Inhibition in CNSIs active nervous process, form of the response to a influence whichis manifested by inhibition or excitation decreasing

Inhibition types

According to connection

with inhibitory neurons

As consequenceof excitation

presynaptic postsynaptic The return pessimal

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Presynaptic inhibition

Development of a slow and long depolarization of the presynaptic termination of excitable neuron is inhibited by neurotransmitter –blockade of carrying out of excitation

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Postsynaptic inhibitionPostsynaptic membrane is

inhibited by

neurotransmitter

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The return inhibition - Oppression of

activity of neuron by a return collateral of

an axon.

Pessimal inhibition - A high frequency of

a stimulation of the neuron causes an

inhibition after excitation

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Value of inhibition

The organism adaptation to

environment

Remission of the CNS of processing of

the insignificant information;

Coordination of motor reactions;

Protection of the nervous centers from

fatigue and attrition

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Structure

of spinal

cord

Spinal cord The spinal cord is the most important structure between the body and the

brain. The spinal cord extends from the foramen magnum where it is

continuous with the medulla to the level of the first or second lumbar

vertebrae. It is a vital link between the brain and the body, and from the

body to the brain. The spinal cord is 40 to 50 cm long and 1 cm to 1.5 cm in

diameter. Two consecutive rows of nerve roots emerge on each of its sides.

These nerve roots join distally to form 31 pairs of spinal nerves. These

nerves are divided into 8 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 1

coccygeal nerve. The spinal nerve contains motor and sensory nerve fibers

to and from all parts of the body. The spinal cord is a cylindrical structure of

nervous tissue composed of white and gray matter.

The gray matter contains the nerve cell bodies and all of the many

thousands of connections between nerves. The white matter is more like a

freeway composed of nerve axon fibers traveling long distances from the

spine to the brain. The ventral root carries motor axon fibers from cells in

the gray matter out to the muscles. Incoming sensory signals pass through

a connection - or synapse – in the dorsal root ganglion, and then follow the

dorsal root into the grey matter.

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Segment

and

covers of

spinal

cord

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Spinal cord covers

The cord is sheathed in the same three connective tissue

meninges as is the brain: the pia (vasculosa),

arachnoid (serosa) and dura (fibrosa). The dura is the

tough outer sheath, the arachnoid lies beneath it, and

the pia closely adheres to the surface of the cord,

blood vessels are located in there

Cerebrospinal fluid (CSF) is located between it and

pia mater (vascular).

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Grey

matter isWhite

matter is

Contact

neuronsBody and dendrites

of motor (efferent)

neurons

Axons of neurons,

which form:

descending (motor)

tracts

ascending (sensory)

tracts

Spinal cord

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Reflex function –participation in

impellent reactions

Conduction –transfering of

nervous impulses

Reflexes of muscles of antagonists:

reduction flexor oppression of a tonus of

extensors

Rhythmic reflexes: alternate action flexor

and extensors of extremities (walking, run)

Tonic reflexes – maintenance of position of

a body in space (a long strain of muscles)

Vegetative reflexes – regulation of work of

an internal, vessels, muscles

• Connection of different

departments of spinal cord;

• Connection of brain with

other department of CNS;

• Поєднання receptors with

виконавчими organs.

Functions of spinal cord