Dr. Farah Nabil Abbas. MBChB, MSc, PhD

Transcription

1 Dr. Farah Nabil Abbas MBChB, MSc, PhD

2 The Basal Ganglia *Functions in association with motor cortex and corticospinal pathways. *Regarded as accessory motor system besides cerebellum. *Receive most of their input signals from cortex itself and in turn return almost all their output signals back to cortex.

3 The Basal Ganglia Located lateral to and surrounds thalamus. Consist of "caudate nucleus, putamen, globus ballidus, substantia nigra, and subthalamic nuclei". Almost all motor and sensory nerve fibers connecting cerebral cortex and spinal cord pass between caudate nucleus and putamen - internal capsule of brain.

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5 The Basal Ganglia Function in association with corticospinal system to control complex patterns of motor activity, i.e., writing letters of alphabet. Damage: cortical system of motor control can no longer provide these patterns.

6 The Basal Ganglia i. cutting a paper with scissors ii. hammering nails iii. shooting basketball through a hoop iv. passing a football v. throwing a baseball vi. movement of shoveling dirt vii. most aspects of vocalization viii. controlled movement of the eyes.

7 Neural Pathways of Putamen Circuit 1. Begins in premotor & supplementary motor areas as well as 1ry somatosensory area. 2. Pass to putamen (bypassing caudate nucleus). 3. To internal portion of globus pallidus. 4. To ventroanterior and ventrolateral relay nuclei of thalamus. 5. Return to 1ry motor cortex and portions of premotor and supplementary motor areas.

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9 Associated Circuits In association with putamen circuit: I. Putamen external globus pallidus subthalamus relay nuclei of thalamus back to motor cortex. II. III. Putamen internal globus pallidus substantia nigra relay nuclei of thalamus return to motor cortex. Local feedback circuits from external globus pallidus subthalamus returning again to external globus pallidus.

10 Abnormalities of Putamen Circuit Functions Portion of circuit damaged or blocked abnormal movements: 1. Globus pallidus lesions spontaneous and continuous writhing (twisting) movement of a hand, an arm, neck, or face called "athetosis".

11 Abnormalities of Putamen Circuit Functions 2. Subthalamus lesions sudden flailing (waving) movement of an entire limb "hemipallismus". 3. Multiple small lesions in putamen flicking movement in hands, face, and other parts of body "chorea". 4. Substantia nigra lesions parkinson's disease.

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13 Basal Ganglia & Cognitive Control Cognition as a term is thinking process of brain using: 1) Sensory inputs to brain 2) Information from stored memory Most of out motor actions occur as a consequence of thoughts generated in mind.

14 Neural Pathways of Caudate Circuit Role in cognitive control of motor activity 1. Input from association areas of cerebral cortex (areas that also integrate different types of sensory and motor information into usable thought patterns). 2. To internal globus pallidus. 3. To relay nuclei of ventroanterior and ventrolateral thalamus.

15 Neural Pathways of Caudate Circuit 4. Back to prefrontal, premotor, and supplementary motor areas (concerned with putting together sequential patterns of movement lasting 5 or more seconds). Note: Almost none of returning signals passing directly to primary motor cortex.

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17 Functions of the Basal Ganglia 1.Control the learned complex pattern motor activity in association with corticospinal system, basal ganglia controls writing. 2.Cognitive control of sequences of motor patterns: Cognitive means the thinking process of the brain using both the sensory input to brain and the information stored in memory. The caudate nucleus plays a major role in the cognitive role of motor sequences e.x. when a person see a lion approach, respond will be: Turning away from the lion. Beginning to run Even attempting to climb a tree. Without cognitive function this process will be performed slowly and after prolonged thinking.

18 o 3.Control the change of time (how rapidly the movement is to be performed), and the scale of movements (how large the movement will be). It is also a function of the caudate nucleus in association with other parts of the cortex, the posterior parietal cortex (responsible for spatial coordination of all parts of the body). Therefore when a patient with left basal ganglia damage draws a person s face he will provide proper proportions for the right side of the face but ignoring the left side (which is in his right field of vision), also he will avoid using the right arm & right hand and almost not knowing that these parts exist. An example of control of time and scale of movements is when writing a letter on a small piece of paper or on chalk board slowly or rapidly you will notice that regardless of your choice the proportional characteristics of the letter remain the same. This is true even if you use fingers at first and then the whole hand later.

19 4.Inhibition of muscle tone, a negative feedback loop from basal ganglia to cortex mediated via GABA & Dopamine (inhibitory neurotransmitter) to control muscle tone all over the body. Destruction to basal ganglia leads to rigidity.

20 5.It plays a role in planning, programming and initiation of most motor activities however they are much grosser and less determinative than when motor cortex contributes as well. 6.Control muscles (axial & girdle) responsible for posture which provides the background for hands and feet discrete movements.

21 Damage to Posterior Parietal Cortex 1. Sensory perception deficits (loss of tactile sensation, blindness, or deafness. 2. Inability to accurately recognize objects through normally functioning sensory mechanisms "agnosia". Example: a lesion in right posterior parietal cortex

22 Personal Neglect Syndrome Severely impaired ability to copy left side of drawings. Person try to avoid: i. Using left arm, left hand, or other portions of left body for performance of tasks ii. iii. Wash this side of body Almost not knowing that these parts of his or her body exist.

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24 Parkinson's disease (Paralysis Agitans) Widespread destruction of portion of substantia nigra (pars compacta) which send dopamine-secreting nerve fibers to caudate nucleus and putamen). Characterized by: 1. Rigidity of much of body musculature. 2. Involuntary tremor of involved areas even when at rest at a fixed rate of 3-6 cycles / second.

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27 Parkinson's disease (Paralysis Agitans) 3. Akinesia (difficulty in initiating a movement). The cause still speculative. However, dopamine secretion in nucleus accumbens of limbic system, is along with its in basal ganglia. It has been suggested that this might reduce psychic drive for motor activity. 4. Postural instability caused by impaired postural reflexes, leading to poor balance and falls. 5. Other motor symptoms including dysphagia, speech disorders, gait disturbances, and fatigue.

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29 Damage to dopamenergic neurons overly overactive caudate and putamen continuous output of excitatory signals to corticospinal motor control system.

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32 Huntigton's Chorea Hereditary disease of 3 rd -4 th decade of life. Flicking movement of individual muscles and then progressive severe distortional movements of entire body Severe dementia with motor dysfunction.