Neurotransmitters

Mediator systems are represented by neurotransmitters, specific nuclei in which these substances are synthesized, mainly in the CNS , and pathways through which these neurotransmitters are released and subsequently bound to receptors.

These pathways carry chemical mediators that aid and stimulate CNS functions. Mediators are highly specific substances and often affect specific areas of the brain.

5 steps of neurotransmission:

1. uptake/synthesis
2. storage
3. release
4. receptor binding
5. inactivation

Cholinergic system

It is made up of neurons synthesizing acetylcholine .

The nuclei are located in the hemispheres and in the brainstem . The main nucleus is the ncl. basalis Meynerti (Ch4), Septum verum, ventral arm of Brock's bundle. It belongs to the basal ganglia and some of the nuclei of the reticular formation . The neurons of the septum verum project to the hippocampal formation, the nc. basalis projects to the entire neocortex, and the RF nuclei send axons to the thalamus .

The cholinergic system has an excitatory effect on neurons and is primarily released at presynaptic terminals in the neocortex, where it facilitates transmission at excitatory cortical synapses.

Acetylcholine is synthesized from choline and acetyl-coenzyme A by choline acetyltransferase (ChAT). Subsequently, Ach is transported by a vesicular transporter into vesicles, where it is stored and then released. Its function is to be involved in the processes of memory and learning, motor function, regulation of wakefulness and sleep, as well as motivation and reward .

In the periphery, Ach plays a role in neuromuscular transmission, is a neurotransmitter of preganglionic fibers of both parasympathetic and sympathetic nerves, and also of postganglionic fibers of parasympathetic nerves, and also plays an important role in pain modulation . It can also occur as a non-neuronal one, being used in immunity, respiration and processes in the skin.

Monoaminergic system

It is formed by groups of neurons located mainly in the nuclei of the reticular formation in the brainstem. The axons of neurons of this system are characterized by rich collateralization and innervation of a large number of CNS structures.

Division of the monoaminergic system:

• catecholaminergic :
  1. noradrenergic – synthesizes noradrenaline
  2. dopaminergic – synthesizes dopamine
• serotonergic – synthesizes serotonin

Dopaminergic system

The dopaminergic nuclei are designated A8-A10 . The most important is the substantia nigra – pars compacta (A9) and medially from it the area tegmentalis ventralis (A10) . The fibers from the substantia nigra project into the striatum and to a lesser extent into the globus pallidus . The fibers emerging from the area tegmentalis ventralis form the so-called mesolimbic dopaminergic system and end in the ventral striatum, ventral pallidum, septum verum, amygdala and cerebral cortex , mainly in the prefrontal and primary motor areas.

Function:

• effect on sympathetic ganglia;
• D1-like family receptors ( D1 and D5 ) − increase the effect of adenylate cyclase ;
• D2 like family receptors ( D2, D3, D4 ) − reduce the effect of adenylate cyclase ;
• The key role of dopamine is motivation , addiction , regulation of the hypothalamic-pituitary system and motor function , and nociception.

• reduced dopamine concentration in the striatum → Parkinson's syndrome (hypokinesia, rigidity, tremor ).
• reduced concentration in the prefrontal cortex → memory disorders, attention, motivation, schizophrenia , depression, substance addiction, eating disorders.

Noradrenergic system

Its neurons are located in the reticular formation of the pontine and medulla oblongata and are referred to as nuclei A1-A7 . The largest and most important noradrenergic nucleus is the locus coeruleus (A7) , located under the floor of the fourth cerebral ventricle. Descending and ascending fibers emerge from it. Descending fibers go to the anterior and posterior horns of the spinal cord , to the sensitive nuclei of the cranial nerves and to the cerebellum, where they end on the dendrites of Purkinje cells. Ascending fibers end mainly in the hypothalamus and thalamus (in the nc. VPL and nc. VPM). Strong projections also go to the neocortex and hippocampal formation. Noradrenergic fibers do not enter the striatum and pallidum.

Function:

• innervation of small vessels of the brain and regulation of cerebral circulation
• noradrenergic fibers are part of the activating ascending system of the reticular formation (ARAS)

Serotoninergic system

Most of the neurons of this system are located in the raphe nuclei of the reticular formation . Their axons enter the ascending and descending bundles, heading to all cortical areas and to all structures of the limbic system . Others end in the striatum, thalamus, hypothalamus, brainstem, cerebellum and spinal cord.

Function:

• activity in the ascending component causes mood changes and behavioral disorders
• fibers ending in the posterior horn of the spinal cord affect the transmission of pain signals , their stimulation causes analgesia
• decreased serotonin synthesis causes depression, sleep disorders and insomnia

Histaminergic system

Most neurons are located in the posterior thalamus , and the histamine they produce affects the transmission of pain signals, motor activity, and thermoregulation .

Glutamate system

Glutamate is the main excitatory mediator in the CNS. It is produced by most mammalian neuronal systems. It is contained in most brain pathways. Prolonged excitatory action caused by the release of glutamate leads to damage and possibly even destruction of the affected neurons.

In order for excitatory AMK to manifest, inhibitory AMK must first be bound.

GABAergní systém

Gamma-aminobutyric acid ( GABA ) [ edit | edit source ]

Inhibitory mediator

Ionotropic GABA A and metabotropic GABA B receptors

Important pathways to the cerebellum, causes opening of chloride channels = hyperpolarization. Modulates monosynaptic and polysynaptic transmission of nociceptive information, presynaptically selects the afferent flow of information to the CNS.

Reduced amounts of GABA : Huntington's chorea , epilepsy, anxiety.

Links

Reference

• DRUGA, Rastislav – GRIM, Miloš. Anatomie centrálního nervového systému. 1. edition. Prague : Galén; Karolinum, 2011. ISBN 978-80-246-1895-1.

• ČIHÁK, Radomír. Anatomie 3. 2. edition. Prague : Grada Publishing, 2004. 692 pp. ISBN 978-80-247-1132-4.