Basal ganglia

Basal ganglia (nuclei basales) are part of the gray matter of the endbrain outside the thalamus, immersed in the white matter of the brain. These are developmentally old structures. They are used in the creation and control of movement, they are also involved in cognitive functions and the functions of the limbic system.

Morphology
thumb|right|400px|BG a jejich propojení Morphologically, the basal ganglia primarily include large nuclei in the basal part of the telencephalon. They are :


 * caudate nucleus; - long, arched C-shaped, lateral to the lateral ventricle, broad head - caput, directed upwards as corpus and continues dorsolaterally as cauda
 * putamen - lateral and basal from nc. caudatus
 * globus pallidus – we divide it into:
 * globus pallidus medialis (pallidum internum) – output basal ganglion;
 * globus pallidus lateralis (pallidum externum) – vintrinsic basal ganglion.

The Nucleus caudatus together with the putamen is referred to as the corpus striatum and the putamen together with the globus pallidus forms the nucleus lentiformis.

The Striatum is divided into: striatum ventrale - rostral part, '''nc. accumbens + tuberculum olfactorium''', important in the feeling of euphoria, satisfaction

striatum dorsale arger part, the fibers coming from other parts to the basal nuclei end here

Pallidum se dělí na : pallidum ventrale - menší, přední část, pod commissura anterior

pallidum dorsale - the larger part above the anterior commissure

The name is derived from the stripes ( striae ) of gray matter that connect these two nuclei through the white matter of the capsula interna.

Developmentally, thecorpus amygdaloideumalso belongs to the basal ganglia, which, however, from a functional point of view is more closely related to the limbic system.

náhled|330x330pixelů|Bazální ganglia Next we describe :
 * Pathways of the basal nuclei
 * Cortical circuit - they connect with the cortex of the telencephalon
 * sensorimotor- one part of the fibers connects the basal nuclei bidirectionally with motor and sensitive ones
 * association circle
 * Limbic circuit
 * Extracortical pathways - smlead to the brainstem to the structures from which the extrapyramidal pathways descend (tectum, nc. ruber, formatio reticularis..)


 * substantia innominata Reicherti – a group of structures basal to the basal ganglia consisting of
 * striatum ventrale / nucleus accumbens – ventral parts of the striatum;
 * pallidum ventrale – ventral part of the globus pallidus;
 * rostral (medial and central) nuclei of the corpus amygdaloideum;
 * nucleus basalis Meynerti – scattered gray matter formed by neurons producing acetylcholine;
 * nucleus subthalamicus (corpus Luysi) – a nucleus located in the subthalamu basally from zona incerta, involved as a so-called intrinsic (intermediate) nucleus in the circuit of the basal ganglia;
 * substantia nigra – a dark nucleus located in the mesencephalon. We distinguish:
 * pars compacta – dopamine-producing monoaminergic nucleus for the corpus striatum (A9 in the system of monoaminergic nuclei);
 * pars reticularis – output basal ganglion.

Function
The basal ganglia are involved in a circuit. The general scheme is: cortex → input basal ganglion → output basal ganglion → thalamus → cortex. Division of basal ganglia according to involvement :


 * basal ganglia input:
 * they receive information from the cerebral cortex;
 * their neurons are inhibitory ( GABA mediator );
 * corpus striatum (ncl. caudatus, putamen, striatum ventrale = ncl. accumbens septum);
 * output basal ganglia:
 * they send information via the thalamus to the cerebral cortex or directly to the brainstem brainstem (reticular formation);
 * their neurons are also inhibitory (GABA);
 * globus pallidus medialis, pallidum ventrale (→ cortex) and substantia nigra, pars reticularis (→ trunk);
 * intrinsic basal ganglia:
 * they transfer information between input and output cores in the so-called indirect path;
 * globus pallidus lateralis (inhibitory neurons – GABA);
 * ncl. subthalamicus (excitatory neurons – glutamate);
 * they modulate the activity of the corpus striatum and direct/indirect pathways via dopamine – pars compacta substantiae nigrae.

Based on which cortical area the stimuli come to the basal ganglia circuit, which nuclei are used as input and output, and which functional cortical area the projection then goes to, we describe the four loops of the basal ganglia.

Direct and indirect track
The basal ganglia are involved in the circuit in the direct and indirect pathways. In the case of a sensorimotor loop, they consist of[ :


 * direct path: cortex – striatum – globus pallidus medialis (pallidum internum) – thalamus – cortex;
 * indirect track: cortex– striatum – globus pallidus lateralis (pallidum externum) – ncl. subthalamicus – globus pallidus medialis – thalamus – cortex.

The basal ganglia are involved in the control of motor functions and partly also in cognitive functions. They generally have a dampening effect on motor skills - on the one hand, through a direct feedback effect on the neurons of the motor cortex,  and on the other hand, by forward damping of cortical stimuli through the reticular formation.

The role of the basal ganglia in motor control
The basal ganglia play an important role in motor control. They are activated before the start of the movement, so they probably participate in its planning. Uhey are also said to be involved in the control of complex movement patterns, such as writing, playing with a ball or speaking. Zapojení bazálních ganglií|thumb Information coming from primarily motor and somatosensitive areas of the cerebral cortex enters the putamen. They continue :


 * direct pathway: the putamen inhibits the globus pallidus medialis with GABA. Globus pallidus medialis is also inhibitory, with its high spontaneous activity dampens the thalamus (GABA). If it is itself inhibited, the inhibition of the thalamus is reduced and it acts excitatory (with the help of glutamate) on the cerebral cortex (mainly the supplementary motor area). Increased activity in this pathway therefore results in higher locomotor activity. Its function is therefore to support movements.
 * indirect pathway: the putamen inhibits the globus pallidus lateralis with GABA. This reduces its inhibitory effect on ncl. subthalamicus, which thus excites the globus pallidus medialis via glutamate. The inhibition of the thalamus through it increases and the excitatory effect on the cerebral cortex is dampened. The indirect path is mainly used to suppress unwanted movements. In the case of its increased activity,movements are suppressed.

right|thumb|350px|Přímá a nepřímá dráha BG

The second output ganglion – pars reticularis substantiae nigrae – is used in the transmission of signals directly to the brainstem and reticular formation and further to the so-called extrapyramidal descending pathways.

Activity in both pathways should be in balance. In the event of its disruption, hyperkinetic or hypokinetic disorders. The pars compacta substatiae nigrae has a major influence on the modulation of the activity of individual pathways through the action of dopamine. The:


 * via D1 receptors increases activity in the direct pathway;
 * through D2 receptors, it reduces the activity in the indirect pathway.

Weakening of dopaminergic influence in the case of degeneration of dopaminergic neurons of the substantia nigra results in increased activity in the indirect pathway leading to hypokinesia (Parkinson's disease).

Caudate circuit
According to some authors, the basal ganglia through the so-called caudate circuit are used in the cognitive control of motor skills. The mechanism described above is then referred to as the putamen circuit and is attributed to the performance of executive functions.

The caudate nucleus is under the influence of association areas of the cortex, integrating sensory and motor information. The output then goes through the globus pallidus medialis, VA and VL nuclei of the thalamus and to the premotor and supplementary motor areas of the cortex. This circuit ensures the subconscious initiation of a motor response, e.g. in a crisis situation.

Cévní zásobení
Na cévním zásobení bazálních ganglií se podílí zejména arteriae centrales anteromediales (z a. cerebri anterior a a. communicans anterior), anterolaterales (také aa. lenticulostriatae, z a. cerebri media) a posteromediales (z a. cerebri posterior a a. communicans posterior).

Klinicky významné jsou:


 * z anteromediální skupiny a. recurrens Heubneri – zásobuje caput ncl. caudati, přední raménko capsula interna, přední část ncl. lentiformis, thalamu, hypothalamu, čichového mozku. Při uzávěru dochází ke kontralaterální hemiparéze s faciální predominancí.
 * z anterolaterální skupiny a. hemorrhagica Charcoti – zásobuje striatum, globus pallidus, přední část capsula interna. Uzávěr vyvolá kontralaterální hemiparézu. Často praská u hypertoniků a bývá příčínou cévní mozkové příhody.

Žilní krev sbírají hluboké mozkové žíly – v. septi pellucidi a v. thalamostriata, které ústí do v. cerebri interna. Ta pokračuje do v. cerebri magna Galeni a ústí do sinus rectus.

Poruchy
Poškození striata (tj. putamen a ncl. caudatus) vyvolává poruchy pohybů, ty jsou pak choreatické a atetoidní, objevuje se hemibalismus a myoklonie. Vzniká hyperkineticko-hypotonický syndrom. Degenerace neuronů striata je příčinou Huntingtonovy chorey.

Poškození globus pallidus vyvolá útlum pohybů i řeči, může vést i ke katalepsii.

Porucha nucleus subthalamicus vede k druhostrannému hemibalismu.

Poškození substantia nigra způsobuje hypokineticko-hypertonický syndrom (Parkinsonův syndrom). Ten je charakterizován svalovou rigiditou, omezením pohybů a klidovým třesem, který mizí při naučených pohybech a ve spánku.

Související články

 * Motorický systém
 * Volní motorika

Externí odkazy

 * The Brain from Top to Bottom
 * NEUROANATOMIE I – Struktury centrálního nervového systému – Bazální ganglia