September 26 - Basal ganglia.docx

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Anatomy and Cell Biology
Anatomy and Cell Biology 3319

September 26, 2013 Basal Ganglia Pp. 402-405 - Identify the main structures - Compare direct and indirect striopallidal pathway - What are the basal ganglia? o Basal  located in the basal part of the forebrain/telencephalon o Ganglia  definition: cluster of neurons in the peripheral nervous system  Basal nuclei, or nuclei basales o A group of nuclei that act as functional unit o Part of the deep gray matter in the forebrain o Strong connections to the cerebral cortex and thalamus o One of the most basic components in the forebrain, can be found in all vertebrates - Where are the basal ganglia? o Cerebral cortex (gray matter)  Superficial cortical layer of gray matter containing neuronal cell bodies o Cerebral white matter  Deeper layer of white matter containing fibers connecting cell bodies to other cortical areas and the rest of the brain  Association fibers  Commissural fibers (corpus callosum)  Projection fibers o Deep gray matter  Basal ganglia – deepest layer of large collections of neuronal cell bodies - Why are the basal ganglia important? o Voluntary movement control  Selection and initiation  Coordination speed and strength of movements o Procedural learning of routines/habits o Cognition o Emotions o Estimation of time Main components of the basal ganglia - Striatum is divided into: o Caudate nucleus, Putamen and Nucleus accumbens - Pallidium is divided into: o Globus pallidus  Internal (GPi) and external (GPe) o Ventral pallidum - Lentiform nucleus o Globus pallidus and putamen - Corpus striatum o Stiatum and Globus pallidus - Anatomical defintion: o Claustrum o Amygdala o Striatum and Pallidum - Clinical definition: o Substantia nigra (SN) – (Mesencephalon)  Pars reticular (SNr)  Pars compacta (SNc) o Subthalamic nucleus (STN) – (Mesencephalon) o Striatum and globus pallidus - (Telencephalon) Basal ganglia and their role in movement control Motor control hierarchy: - Strategy/Goal: o Association area of the cortex:  Prefrontal cortex  Ideomotor area o Basal ganglia - Tactics: sequence of muscle contractions o Motor cortex o Premotor cortex o Cerebellum - Execution: activation of motor neurons o Brainstem o Spinal cord (spinal reflexes) The striopallidal pathway - Move from cortex through the basal ganglia to the thalamus and then back to the cortex - Usually the thalamus has an excitatory connection to the motor areas o If thalamus is activated, you activate the motor areas - You don’t want to move all the time (involuntary movement), so you want to inhibit the thalamus o This is done by tonic inhibition through the GPi (internal globus pallidus) o Blocks excitatory connection to motor areas - Direct pathway – GO (initiate a movement) o You need input from the cortex AND the SNc (substantia nigra pars compacta) o In the striatum the inputs are combined o Neurons are activated that have the D1 receptors – these neurons inhibit the GPi, so you release the tonic inhibition of the thalamus o Therefore activate the motor areas – increased cortical activation - Second pathway to stop the movements is through the STN (subthalamic nucleus) o STN can activate the GPi to reinforce the inhibition on the tha
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