Basal ganglia Medical Presentation

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Published on : Mar 10, 2019 | Views : 2344 | Downloads : 11

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Basal ganglia SPP4
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objectives Part of Basel ganglia. Functions of Basel ganglia. Blood supply of Basel ganglia. Connection of afferent and efferent of Basel ganglia. Lesion of Basel ganglia
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parts of basal ganglia
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Nuclei of the Basal Ganglia The anatomy of the basal ganglia is complex since it is spread throughout the forebrain. Its components can be divided into input nuclei, output nuclei and intrinsic nuclei. Input nuclei receive information, which is then relayed to intrinsic nuclei for processing, and further passed to output nuclei Input Nuclei Caudate nucleus and putamen (neostriatum) 01 Intrinsic Nuclei External globus pallidus Subthalamic nucleus Pars compacta of the substantia nigra 02 Output Nuclei Internal globus pallidus Pars reticulata of the substantia nigra 03
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Caudate Nucleus The caudate nucleus forms the lateral wall of the lateral ventricle and follows the telencephalic expansion during development. It has a characteristic ventricular C-shape when fully developed. It can be identified as the collection of gray matter on the wall of the lateral ventricles. During development, the caudate nucleus is separated from the putamen by descending white matter fibres, which at this level are known as internal capsule
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Lentiform Nucleus (Globus Pallidus and Putamen) The lentiform nucleus is comprised of globus pallidus and the putamen. Although anatomically related, they share no functional relationship. It can be identified as a collection of gray matter laying deep within the hemispheres. The putamen forms the lateral aspect of the lentiform nucleus. On its concave inner surface lies the most exterior of the globus pallidus, the GPe, and the most internal structure is the GPi. The putamen is separated from the GPe by the lateral medullary lamina, and the medial medullary lamina separates the GPe from the GPi
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Substantia Nigra The substantia nigra is conspicuous in gross specimens and can be seen in cuts through the midbrain, having a dark appearance due to the neuromelanin present in the cells of the SNc.
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Subthalamic Nucleus The subthalamic nucleus, as the name implies, lies inferior to the thalamus, and right above the substantia nigra
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Functions of basal ganglia
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Control of muscle tone. Functions Control of automatic associated movement Control of motor activity. Role in Arousal mechanism. Role of neurotransmitter in the functions of basal ganglia
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Control of Muscle Tone The lentiform nucleus decreases the muscle tone Mechanism: by decreasing the activity of the alpha neurons through: Caudate nucleus increases the muscle tone Mechanism: by stimulating the facilitatory reticular formation (gamma), the vestibular & inferior olivary nuclei (alpha). Inhibition of the primary motor cortex (i.e. area 4), vestibular nucleus. Inhibiting the facilitatory reticular formation inhibition of Gamma. Stimulating the inhibitory reticular formation (gamma) & red nucleus (alpha). Generally it is inhibitory to the muscle tone
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Control of Motor Activity Regulation of voluntary movement Control complex patterns of motor activity e.g. writinga. Skilled movements performed subconsciously e.g. cutting paper with scissors, hammering nails. Cognitive control of motor activity Cognition = thinking process using sensory + memory stored. (i.e. converting thoughts into motor actions). Control timing and intensity
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3. Control of automatic associated movement. As a part of the extrapyramidal system, the BG initiate subconscious automatic movements (e.g. swinging of the arms during walking) and produce postural adjustments that maintain equilibrium.
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Blood supply of Basel ganglia
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Blood supply Blood supply of the basal ganglia is provided via three arteries, anterior choroidal, middle cerebral and anterior cerebral. The caudate nucleus with its extended gray mass is C-shaped with a head, that is continual with the putamen, a body and a tail.
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Connection of basal ganglia
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Striatum receives afferent inputs from motor and premotor areas of cerebral cortex. From striatum impulses, efferent impulses reach pars reticulata of substantia nigra. Efferent impulses from striatum also reach globus pallidus. i. Striatum to substantia nigra—striatonigral pathway. ii. Striatum to globus pallidus—striatopallidal pathway. From pars compacta region, efferent connection going to striatum is known as nigrostriatal pathway. The neurotransmitter released by this pathway is dopamine. From globus pallidus, impulses go to subthalamic nucleus. Impulses will also come back to globus pallidus (efferent) from subthalamic nucleus. Also, efferent impulses from subthalamic nucleus will reach pars reticulata of substantia nigra. Basel ganglia: its closed circuit of connection. There is a lot of mutual influence between various nuclei of basal ganglia.
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From globus pallidus, impulses (efferent) come to centromedian, ventroanterior and ventrolateral nuclei of thalamus. From centromedian nucleus, efferent impulses reach striatum. From ventrolateral, ventroanterior and centromedian nuclei impulses are relayed back to motor and pre-motor areas of cerebral cortex. So whole of basal ganglia connection is like a closed loop.
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Lesions of basal ganglia
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Chorea Definition : sudden spontaneous purposeless involuntary dancing movements (jerky with short duration) affect all muscles EXCEPT external ocular muscle. Lesion : in caudate nucleus ( degeneration of neurons in caudate nucleus and putamen that secret GABA i.e inhibitory transmitter). Causes of chorea : 1- Rheumatic fever( in children) 2- Toxemia of pregnancy 3- Gene defect (Huntington’s disease)
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Parkinson’s disease Site of lesion : in substantia nigra mostly due to depletion of dopamine secretion from nigro-striate fibers. Manifestations of Parkinsonism : (1)Rigidity: stuffiness in muscles during movement Flexor (ghorilla like) attitude. Cog-wheel rigidity or lead pipe rigidity. (2) Tremors : rhythmic alternating contraction of opposing muscle groups Static. Mainly in distal joints.
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Akinesia Its loss of subconscious associated movement. Mask ( expressioniess ) face Slow, low and monotonus speech. Shuffling (festinating) gait. False paralysis ( paralysis agitans) Intolerance to cold
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