Blood Supply To The Subthalamus

Basal Ganglia – derived from telencephalon/ some diencephalon/mesencephalon Structure: Striatum: Caudate Nucleus Putamen Globus Pallidus External/Lateral Segment GPe Internal/Medial Segment GPi *Lentiform/Lenticular Nucleus: Putamen and Globus Pallidus *Corpus Striatum: Caudate Nucleus/Putamen/Globus Pallidus Substantia Nigra -pars compacta DOPAMINERGIC – dorsal SNc - pars reticulate GABAergic – ventral SNr Subthalamic Nucleus Nucleus Accumbens – ventral StriatumDOPAMINERGIC Blood Supply: Anertior Cerebral Middle Cerebral Posterior Communicating SYNAPTIC CIRCUITS/ NEUROTRANSMITTERS 1. Cortex- (glutamate)Striatum (Ach, Gaba, enkephalin, substance P 2. Direct Pathway: Thalamus disinhibited/Excited; movement is facilitated Striatum(GABA/Substance P)GPi & SNr (GABA) Thalamus Premotor & SMA 3. Indirect Pathway: Thalamus is inhibited and movement is inhibited Striatum( GABA& Enkephalin)GPe (GABA) subthalamic Nucleus (glutamate) GPe, GPi& SNr (GABA)ThalamusPremotor & SMA 4. Nigrostriatal Pathway: dopaminergic; facilitates movement by acting on bot indirect/direct pathways

5. Dopamine Affects 2 Different output Neurones in the Striatum: -D1 Dopamine Receptors : Excite Direct Pathway Movement -D2 Dopamine Receptors: Inhibit Indirect PathwayMovement (inhibit the inhibitory pathway/disinhibition) *DOPAMINE Indirect/Direct Pathway= MOVEMENT MAJOR CONNECTIONS OF THE BASAL GANGLIA A. Connections OUTSIDE the basal Ganglia Extrinsic inputs to the basal ganglia terminate mainly in the striatum FROM: 1. Corticostrial Pathway- Cerebral Cortex (motor, sensory, association, limbic): topographical projections 2. Intralaminar Nuclei of the Thalamus: topographically organized

Extrinsic Outputs from the basal ganglia arise mainly from the globus paliidus and substantia nigra pars reticula TO: 1. Motor Nuclei of the Thalamus 2. Superior Colliculous of the Midbrain

B. Connections within the Basal Ganglia 1. Caudate and Putamen: • Striatopallidal pathway :Project to globus pallidus • Nigrostriatal/ Striatonigral Pathway: Reciprocally connect with substantia nigra ○ SNcStriatumSNr 2. Subthalamic Nucleus • Receives input from the motor and premotor corticies • Reciprocally connected with the globus pallidus • Projects to substantia nigra, pars reticulate 3. Substantia Nigra: • Receives from and projects to the striatum

General Functional Significance of the Basal Ganglia A. Involved in the regulation of movement: through direct and indirect connections with the cerebral cortex, the basal ganglia influence descending motor systems (e.g., corticospinal and corticobulbar). B. Forms the major component of the extrapyramidal motor system; however, there is extensive interconnections and cooperation between the extrapyramidal and the pyramidal systems in the control of movement. C. Involved in the control of eye movements and in the memory of orientation in space. D. Contributes to cognition. E. Related to limbic functions. Dysfunctions of the Basal Ganglia : Abnormal movements are commonly caused by a release of the system from inhibition. Disorders of the basal ganglia is usually a disruption of transmitter metabolism. • Involuntary movements: Tremor at rest (Parkinsons), Athetosis (slow movement), Chorea, Ballism, Dystonia (disordered movement). Akinesia (loss of movement) and bradykinesia (slow movement) • Changes in posture & muscle tone/ Muscle rigidity Diseases of Basal Ganglia: 1. Parkinson’s Disease (too few movements) • Degeneration of dopaminergic cells in SNc • Tremor at rest, rigidity, bradykinesia 2. Huntington’ s Disease (too many movements) • Degerenation of Ach and GABA neurons in the striatum

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Inherited mutation in chrom. 4 causes numerous CAG repeats (Glutamine) more repeates=earlier onset • Chorea, athetosis, dystonia 3. Tardive Dyskinesia : long term use of antipsychotic agents (block dopaminergic transmission) • Involuntary movements of face/ tongue 4. Hemiballismus: Lesion of the subthalamic nucleus • Violent ball throwing movements of contralateral arm COMPARISONS CEREBELLUM BASAL GANGLIA • Direct input from Spinal cord NONE • No direct output to Spinal Cord No direct output to spinal cord • Connections with Brainstem Connects w/ and is part of Brainstem • Indirect input from cortex via Pons (motot/premotor) Direct input from wide areas of Cortex • Projects via thalamuscortex Projects via thalamus cortex • Output is Excitatory Output is inhibitory Deep cerebella nuclei internal segment of globus palludus • Coordinates Execution of movement : Planning/Execution of complex motor compares intended w/executed strategies: Amplitude/Velocity of movement • LesionIpsilateral Symptoms LesionContrallateral /Bilateral • Ataxia, Impaired balance, Eye movements Too much/too little movement • Intentional Tremor Tremor at Rest