Basal Ganglia - BMS2-18 PDF

The Basal Ganglia Also known as the basal nuclei https://www.youtube.com/watch?v=s-6sOscx8-E : A 3-D tour Basal Ganglia: Neuroanatomy Video Lab - Brain Dissections – YouTube : Eccles Health Sciences The Basal Ganglia • Groups of neurons within CNS – subcortical grey masses • Function together -...

The Basal Ganglia Also known as the basal nuclei https://www.youtube.com/watch?v=s-6sOscx8-E : A 3-D tour Basal Ganglia: Neuroanatomy Video Lab - Brain Dissections – YouTube : Eccles Health Sciences The Basal Ganglia • Groups of neurons within CNS – subcortical grey masses • Function together - interconnected • Common inputs, common targets, common neurotransmitters • Neural basis of habitual sequential motor behaviours • Bahaviours that once are activated (by internal or external stimuli) are completed without constant conscious oversight • Initiation of voluntary movements • Supression of movements to keep motor cortex quiet • Prevent unwanted movement at rest  Reduce or dampen excitatory output of cerebral cortex (thru the thalmus) • Also have non-motor cognitive functions The Basal Ganglia Components: 5 major nuclei The Basal Ganglia Components: 5 major nuclei Lenticular nuc. Basal Ganglia • Group of nuclei forming part of each cerebral hemisphere • Internal structures  visible only in sections • Major basal ganglia: Caudate nucleus Lenticular nucleus - subdivided into putamen globus pallidus • Lenticular nuc. separated from thalamus & head of caudate nuc by internal capsule The Basal Ganglia Components: 5 major nuclei Caudate Putamen + Lenticular nucleus Globus Pallidus Caudate nucleus + Lenticular nucleus Dorsal striatum The Basal Ganglia Components: 5 major nuclei The Basal Ganglia Components: 5 major nuclei The Basal Ganglia Components: 5 major nuclei The Basal Ganglia Olfactory tubercle + Nucleus acumbens Ventral striatum The Basal Ganglia Components: 5 major nuclei Caudate Putamen Cerebral hemisphere (Striatum) Corpus striatum Globus Pallidus Cerebral hemisphere (Pallidum) Substantia Nigra Brain stem Subthalamic Nucleus Diencephalon Functionally, corpus striatum is closely related to subthamus & substantia nigra The Basal Ganglia Coronal Section At ant horn of lateral ventricle & optic chiasm The Basal Ganglia Coronal Section Unstained section C: Caudate P: Putamen GP: Globus Pallidus i: internal e: external The Basal Ganglia More Dorsal Coronal Section Unstained section SN: Substantia nigra STn: Subthalamic nucleus The Basal Ganglia More Dorsal Coronal Section Unstained section Substantia nigra Caudate Putamen More Dorsal Coronal Section The Basal Ganglia Substantia Nigra Nigra (L): Black • Appears darker than neighboring areas due to high levels of neuromelanin in dopaminergic neurons • Consists of 2 parts w/different connections & functions: Pars compacta • Output to the basal ganglia circuit • Supplies striatum w/ dopamine Pars reticulata • Mainly serves as an input • Conveys signals from the basal ganglia to numerous other brain structures Clinical Correlate Parkinson's disease characterized by loss of dopaminergic neurons in the substantia nigra pars compacta Functions & Connections of the Basal Ganglia • Facilitates approriate motor programs (movements) • Supression of movements to keep motor cortex quiet • Prevent unwanted movement at rest • 2 paralell loop circuits with opposite functions • Direct pathway • Indirect pathway • Both circuits relay thru thalamic VA & VL nuclei • Connections are all in ipsilateral cortex Interconnections of the Basal Ganglia • Direct pathway: Increases cortical excitation & initiates movement • Indirect pathway: Decreases cortical activation & supresses movement • Dopamine: Excites direct pathway receptors (D1) Inhibits indirect pathway receptors (D2) • Acethylcholine: Excites indirect pathway Basal Ganglia Pathways • Connections are ipsilateral • Signs are contralateral bcs of crossing of corticospinal tract (pyramidal system) SNc: Substantia Nigra, pars compacta VTA: Ventro tegmental area Chorea • https://www.youtube.com/watch?v=PsFJkL3x10o • To initiate a particular movement, the cerebral cortex sends a signal to the basal ganglia that causes the inhibition to be released. • Damage to the basal ganglia can cause the release or reinstatement of the inhibitions to be erratic and uncontrolled, which results in an awkward start to motion or motions to be unintentionally initiated, or a motion to be halted before, or beyond, its intended completion. • The accumulating damage to this area causes the characteristic erratic movements associated with Huntington’s D. • The spontaneous and erratic physical movements associated with HD are classified as a type of hyperkinetic dysarthria. • Because of the basal ganglia's inability to inhibit movements, individuals affected by it will inevitably experience a reduced ability to produce speech and swallow foods and liquids (dysphagia)