Autonomic (ANS) or vegetative nervous system (VNS)



ANS is a complex of central and peripheral cellular structures regulating organism internal life functional level necessary for all systems adequate reaction.

ANS together with the endocrine (hormone), controls the body’s internal organs. It:

· innervates smooth muscle;

· cardiac muscle;

· glands;

· controlling blood circulation;

· gastro-intestinal tract activity;

· body temperature etc.

Most of this control is not conscious.

ANS is divided into 3 main parts:

– sympathetic nervous system (SNS);

– parasympathetic nervous system (PNS);

– metasympathetic nervous system (MNS).

 

Vegetative and somatic nervous system comparative characteristics

 

Features Vegetative Somatic
Target organs Smooth muscles, myocardium, glands, fatty tissue, immunity organs Skeletal muscles
Ganglii Paravertebral, prevertebral and organic Located in CNS
Efferent neurons number Two One
Effect of stimulation Exciting or inhibiting Exciting
Nervous fibers types Thin myelinized or non-myelinized, slow Myelinized fast

 

ANS mediator mechanisms

 

Mediator Receptor Effect mechanism
Acetylcholine Nicotinic n-cholinoreceptor Na+-K+-channels activation
Acetylcholine Muscarine M1-M4-cholinoreceptors Effect on inositol-3-phosphate, cAMP, cGMP as well as G-protein-mediated effect on K+-channels
Noradrenaline α1α2β1β2-adrenoreceptors Effect is based on cAMP, inositoltriphosphate, phospholipase C, G-protein-mediated effect on K+ and Ca++ - channels

 

Organs with monosympathetic innervation:

1) blood vessels;

2) spleen capsule;

3) hair bulbs smooth myocytes;

4) pancreatic insulas cells.

Organs with monoparasympathetic innervation:

1) arteries of penis, clitoris, small sexual lips;

2) lacrimal glands;

3) pupil’s sphincter;

4) hypophysis;

5) suprarenal medulla.

Vegetative ganglii features:

1) connective tissue absence;

2) insignificant extracellular spaces;

3) many glial elements;

4) excitement wave one-sided conductance;

5) excitement convergency and divergency;

6) temporary and space summation;

7) occlusion;

8) nervous impulses rhythm transformation;

9) long-termed synaptic delay (1,5-30 msec);

10) EPSP;

11) prolonged trace hyperpolarization;

12) impulses rate is equal to 10-15 impulses per second;

13) autonomic regimen.

ANS mediators:

1) acetylcholine;

2) noradrenaline;

3) ATP;

4) histamine;

5) substance P;

6) angiotensine;

7) prostaglandine E;

8) serotonine.

ANS parts:

1) cranial-bulbar – nuclei of III, VII, IX and X pairs;

2) sacral – pelvic nerve;

3) thoracical-lumbal – spine lateral corns nuclei.

ANS floors

1) intramural plexuses – metasympathetic nervous system;

2) paravertebral and prevertebral ganglii;

3) SNS and PNS central structures – preganglionary neurons accumulation in brain stem and spine;

4) the highest vegetative centers:

· hypothalamus;

· cerebellum;

· reticular formation;

· basal ganglii;

· big hemispheres cortex.

ANS total structural plan

Central (preganglionar) neurons:

A. parasympathetic nervous system –

· in a brain stem (nuclei of III, VII, IX, X th pairs of cranial-cerebral nerves;

· in SII-SIV of spine;

B) sympathetic nervous system –spine lateral corns C8-L2-4 or thoraco-lumbal center of Yacobson.

Their processes – preganglionary neurons – come to corresponding vegetative ganglii:

a) sympathetic – to:

· paravertebral;

· prevertebral;

b) parasympathetic – to:

· intramural.

Here, in ganglii, they are finished with synapses on postganglionary neurons.

Postganglionary fibers – axons of postganglionary neurons – come directly to the organ.

Effects of autonomic nervous system of selected organs

 


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