Basal ganglia physiology

guyton

1. Basal ganglia

2. On each side of the brain, these ganglia consist of the caudate nucleus, putamen , globus pallidus , substantia nigra , and subthalamic nucleus. They are located mainly lateral to and surrounding the thalamus, occupying a large portion of the interior regions of both cerebral hemispheres.

3. Two main circuits T he Putamen Circuit For executing learned patterns of movement. T he Caudate Circuit For Cognitive Control of Sequences of Motor Patterns.

4. The term cognition means the thinking processes of the brain, using both sensory input to the brain plus information already stored in memory. Most of our motor actions occur as a consequence of thoughts generated in the mind, a process called cognitive control of motor activity. The caudate nucleus plays a major role in this cognitive control of motor activity.

5. Functions of basal ganglia Function in association with the corticospinal system to control complex patterns of motor activity (cutting paper with scissors, hammering nails, shooting a basketball through a hoop, passing a football, throwing a baseball etc. Cognitive control of motor activity e.g. if a person comes across a lion he will subconsciously plan 1) turning away from the lion, (2) beginning to run, and (3) even attempting to climb a tree To Change the Timing and to Scale the Intensity of Movements

6. A lesions of the posterior parietal cortex produce an inability to accurately perceive objects through normally functioning sensory mechanisms, a condition called agnosia .

7. In case of lesion in the right posterior parietal cortex ,the patient's ability to copy the left side of the drawings is severely impaired. Also, such a person will always try to avoid using his or her left arm, left hand, or other portions of his or her left body for the performance of tasks, or even wash this side of the body ( personal neglect syndrome ), almost not knowing that these parts of his or her body exist.

8. Diseases of the Basal Ganglia in Humans Three distinct biochemical pathways in the basal ganglia normally operate in a balanced fashion: (1) the nigrostriatal dopaminergic system, (2) the intrastriatal cholinergic system, and (3) the GABAergic system, which projects from the striatum to the globus pallidus and substantia nigra . When one or more of these pathways become dysfunctional, characteristic motor abnormalities occur. Diseases of the basal ganglia lead to two general types of disorders: hyperkinetic and hypokinetic .

9. Athetosis consists of slow, writhing movement of the distal parts of the limbs. Chorea is characterized by rapid, flicking movement of the extremities and facial muscles. Ballism is associated with violent, flailing movement of the limbs (ballistic movement). Akinesia is difficulty in initiating movement and decreased spontaneous movement. Bradykinesia is slowness of movement.

10. Abnormal Function in the Putamen Circuit: Athetosis , Hemiballismus , and Chorea when a portion of the circuit is damaged or blocked, certain patterns of movement become severely abnormal. lesions in the globus pallidus frequently lead to spontaneous and often continuous writhing movements of a hand, an arm, the neck, or the face-movements called athetosis . A lesion in the subthalamus often leads to sudden flailing movements of an entire limb, a condition called hemiballismus .

11. Huntington Disease An autosomal dominant inherited disease, with the onset occurring most often in adult life(30-40years). Death occurs 15 to 20 years after onset. The disease has been traced to a single gene defect on chromosome 4. This gene encodes a protein, huntingtin , the function of which is not known. The codon (CAG) that encodes glutamine is repeated many more times than normal. The disease affects men and women with equal frequency.

12. Damage to GABnergic neurons of caudate nucleus and putamen to the globus pallidus external segment releases inhibition, permitting the hyperkinetic features of the disease to develop. Signs and symptoms: Choreiform movements first appear as involuntary movements of the extremities and twitching of the face (facial grimacing). Later, more muscle groups are involved. Speech becomes slurred and then incomprehensible. Progressive dementia occurs with loss of memory and intellectual capacity.

13. Parkinson Disease Has both hypokinetic and hyperkinetic features Is a progressive disease of unknown cause that commences between the ages of 45 and 55 years. It is associated with neuronal degeneration in the substantia nigra

14. The dopamine secreted in the caudate nucleus and putamen is an inhibitory transmitter; Destruction of the dopaminergic neurons in the substantia nigra allow the caudate nucleus and putamen to become overly active and possibly cause continuous output of excitatory signals to the corticospinal motor control system. These signals could overly excite many or all of the muscles of the body, thus leading to rigidity .

15. Types of Parkinson disease According to the cause Postencephalitic parkinsonism developed following the viral encephalitis outbreak of 1916–17 in which damage occurred to the basal nuclei. Iatrogenic parkinsonism can be a side effect of antipsychotic drugs (e.g., phenothiazines ). Meperidine analogues (used by drug addicts) and poisoning from carbon monoxide and manganese can also produce the symptoms of parkinsonism. Atherosclerotic parkinsonism can occur in elderly hypertensive patients

16. Tremor. This is the result of the alternating contraction of agonists and antagonists. The tremor is slow and occurs most obviously when the limbs are at rest. It disappears during sleep. Rigidity . This differs from the rigidity caused by lesions of the upper motor neurons in that it is present to an equal extent in opposing muscle groups. If the tremor is absent, the rigidity is felt as resistance to passive movement and is sometimes referred to as plastic rigidity (lead pipe). If the tremor is present, the muscle resistance is overcome as a series of jerks, called cogwheel rigidity.

17. Bradykinesia Akinesia Mask like face :The movements are slow, the face is expressionless, and the voice is slurred and unmodulated . Staccato and stiff movements . Swinging of the arms in walking is lost. Postural disturbances . The patient stands with a stoop, and his or her arms are flexed. The patient walks by taking short steps and often is unable to stop. In fact, he or she may break into a shuffling run to maintain balance.

18. There is no loss of muscle power and no loss of sensibility. Since the corticospinal tracts are normal, the superficial abdominal reflexes are normal, and there is no Babinski response. The deep tendon reflexes are normal. other motor symptoms including dysphagia (impaired ability to swallow), speech disorders, gait disturbances, and fatigue.

19. Treatment Treatment with l - Dopa Treatment with l - Deprenyl ( inhibits monoamine oxidase ) Treatment with Transplanted Fetal Dopamine Cells Treatment by Destroying Part of the Feedback Circuitry in the Basal Ganglia