Basal Ganglia PDF

BASAL NUCLEI (BASAL GANGLIA)  Basal nuclei and cerebellum affects the motor areas of cerebral cortex through the VL and VA nuclei of thalamus They also may effect the spinal cord motor mechanisms through their brainstem connections  Basal nuclei are a group of paired nuclei...

BASAL NUCLEI (BASAL GANGLIA)  Basal nuclei and cerebellum affects the motor areas of cerebral cortex through the VL and VA nuclei of thalamus They also may effect the spinal cord motor mechanisms through their brainstem connections  Basal nuclei are a group of paired nuclei which are situated within the deep part of the white matter of the cerebral hemispheres Most of them lie lateral to the thalamus and separated from it through the internal capsule. Traditionally called ganglia  Have important role in voluntary movement (fine coordination of complex movements through regulating the cerebral activity - more complex movements than cerebellum controls) and control of posture Have no direct input or output connections with the spinal cord Their influence on the motor functions is through the cerebral cortex and brainstem  Basal nuclei also have influence on cognitif, mood and some non-motor behaviours – These functions are carried through their connections with the orbito-frontal cortex and mesocorticolimbic dopaminergic system Due to this, in basal nuclei lesions besides motor disturbances some psychiatric disturbances may also be observed Composed of five nuclei – Caudate nucleus – Putamen – Globus pallidus – Substantia nigra – Subthalamic nucleus  According to some authors amygdaloid body is also considered as part of the basal ganglia, however, its well established functions are mostly related with the limbic system (regarded as the center of fear and aggressiveness) Claustrum is situated in the close vicinity of the basal ganglia, however its function is recently described as on/off center for the brain Putamen LENTIFORM Globus pallidus NUCLEUS Lentiform nucleus CORPUS Caudate nucleus STRIATUM Caudate nucleus NEOSTRIATUM Putamen (STRIATUM) Caudate nucleus C-shaped nucleus, formed of head, body and tail Lies lateral to the thalamus Laterally separated from lentiform nucleus by the anterior limb of the internal capsule The groove between the head of caudate nucleus and the thalamus is called the terminal sulcus, within which lie the stria terminalis (conveys efferent fibres from amygdaloid body to hypothalamus)  Caudate nucleus and putamen forms a functional unit known as neostriatum (or striatum) and their afferent and efferent connections are same – Afferents of the neostriatum arise from cerebral cortex, thalamus, subthalamic nucleus and brainstem – Efferents of the neostriatum projects to the globus pallidus and substantia nigra Lentiform nucleus Formed of a lateral darker portion, the putamen and medial portion, globus pallidus Anterior limb of the internal capsule separates lentiform nuscleus from the caudate nucleus, whereas the posterior limb separates it from the thalamus External capsule lies between the lentiform nuscleus and the claustrum Putamen Lies between the globus pallidus and external capsule Globus pallidus Formed of two parts; globus pallidus lateralis (GPL) and globus palllidus medialis (GPM)  Afferents of globus pallidus arise from the neostriatum, the subthalamic nucleus and pars compacta of the substantia nigra Efferents of globus pallidus forms ansa lenticularis, fasciculus lenticularis, fasciculus thalamicus ve fasciculus subthalamicus (pallidosubthalamic fibers), pallidotegmental fibers  Ansa lenticularis and fasciculus lenticularis are formed of fibers originating from the globus pallidus medialis and globus pallidus lateralis respectively – They unite to form the thalamic fasciculus and terminate in the thalamic nuclei Fibers of fasciculus subthalamicus originate from the globus pallidus lateralis and terminate in the subthalamic nucleus Pallidotegmental fibers terminate in the tegmentum of midbrain Substantia nigra It is situated in the mesencephalon, between the cerebral peduncles and tegmentum Formed of two parts, pars compacta and pars reticularis Subthalamic nucleus Subthalamus is a complex formed of fibers and nucleus groups Structures constituting the subthalamus are subthalamic nucleus, nuclei campi perizonalis, zona incerta, ansa lenticularis and fasciculus subthalamicus Most of the afferents of the subthalamic nucleus arise from the globus pallidus lateralis, its efferents project to the globus pallidus and substantia nigra SUMMARY of the CONNECTIONS of the BASAL GANGLIA AFFERENTS Almost all of the afferents to the basal ganglia terminate in the neostriatum (afferent center of the basal ganglia) Main afferents arise from the cerebral cortex, intralaminar nuclei of thalamus, pars compacta of the substantia nigra and the brainstem EFFERENTS Efferents of the neostriatum terminate in the globus pallidus and pars reticularis of the substantia nigra Most of the efferents from the basal ganglia arise from the globus pallidus medialis – These efferents mainly terminate in the thalamus, subthalamic nucleus and pars reticularis of the substantia nigra – The thalamic nuclei receiving these efferents relay these fibers to project to the motor, premotor and mostly to the supplementary motor areas as well as the prefrontal areas of the cerebral cortex  FUNCTIONAL SIGNIFICANCE of the BASAL GANGLIA Basal ganglia influence the motor activity either by activating or inhibiting the motor activity of the cerebral cortex through thalamus The influence of the basal ganglia on the motor activity of the cerebral cortex is achieved by two connections – Direct pathway (excitatory to the activity of the motor cortex) – Indirect pathway (inhibitory to the activity of the motor cortex)  Normally, spontaneous activity of the GPM and pars reticularis of the SN inhibits the activator influence of the thalamus on the cerebral cortex Direct pathway inhibits the spontaneous activity of the GPM and pars reticularis of the SN, therefore tahalamus increases the cortical motor activity Indirect pathway increases the spontaneous activity of the GPM and pars reticularis of the SN through subthalamic nucleus and decreases the cortical motor activity Additionally, dopaminergic neurons in the pars compacta of the SN can increase the cortical activity by activating the direct pathway and by inhibiting the indirect pathway  Direct and indirect pathways functions in harmony and in accordance with the necessities in influencing the motor activity Hypokinetic or hyperkinetic (chorea, athetosis, ballism) signs are seen in the disorders of the basal nuclei Parkinson’s disease bears both hypokinesia as well as hyperkinetic involuntary movements  Damage to the primary motor areas of the cerebral cortex impairs the fine discrete movements of the distal parts of the limbs on the contralateral side, though gross crude movements are prevented Damage to the primary motor areas of the cerebral cortex, together with damage to neostriatum, leads to a complete paralysis of the limbs on the contralateral side  Parkinson Nigrostriatal yol Hemiballismus X Inhibitor neurons of X GPM can not be activated  Chorea X Inhibitor neurons of X Overactivity of these GPM can not be neurons inhibit activated subthalamus Clinical note Chorea Involuntary quick, jerky movements such as swift grimaces and sudden movements of the head and limbs Huntington’s disease – Autosomal dominant inherited disease – There is a degeneration of GABA, substance-P and acetylcholine secreting neurons of the striatonigral pathway – As a result, neurons in SN become overactive and inhibit the neostriatum – Inhibiton of inhibitory effect of neostriatum on the indirect pathway leads to the abnormal movements that are seen in this disease Signs are – Choreiform movements: Involuntary movements of the extremities and twitching of the face, later involving more muscle groups – Progressive dementia: Loss of memory and intellectual capacity Chorea Clinical note Hemiballismus Sudden, violent, involuntary movements of the proximal limb muscles of one side Lesion is in the opposite subthalamic nucleus or its connections Athetosis Slow, sinuous, writhing movements mostly involving the distal limb muscles There is degeneration in globus pallidus KLİNİK BİLGİ Huntington’s disease – Inherited (autosomal dominant mutation in gene called Huntingtin) – Diffuse neuronal loss in brain; first effecting the striatum, especially the caudate nucleus – GABAergic neurons are effected – Inhibition of indirect pathway – Beside chorea and athetosis, there is progressive demans (loss of meomory and intellectual capacity)  Huntington X Inhibitor neurons of X Overactivity of these GPM can not be neurons inhibit activated subthalamus Huntington hastalığı Clinical note Parkinson’s disease Most commonly seen disease of the basal ganglia of unknown caus Neuronal degeneration is seen in many parts of the basal ganglia Patient presents the following signs – Tremor in rest (static tremor) – Rigidity (flexor and extensor muscle groups contract simultaneously) – Akinesis and bradykinesis (difficulty in initiating and performing a movement, decreased amplitude during movement) i.e. walking by short steps and difficulty in stopping – Poker face May be treated with increasing the brain dopamine level As dopamine can not pass the blood brain barrier its precursor L-dopa is used Lately, transplantation of dopamine secreting embryonic cells into the caudate nucleus and putamen has proven to be successful in certain cases