Extrapyramidal system
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In human anatomy, the extrapyramidal system is a neural network located in the brain that is part of the motor system involved in the coordination of movement. Extrapyramidal neurons, like related gamma system neurons, excite or inhibit anterior horn cells. The extrapyramidal system is primarily regulated by the nigrostriatal pathway. The system is called "extrapyramidal" to distinguish it from the primary motor cortex. Many of the neuron bodies belonging to the primary motor cortex are shaped like pyramids.
Reflex activities of a target muscle are affected by motor signals from the corticospinal tract and by the influence of extrapyramidal signals. Extrapyramidal tracts originate from different part of the brain as the red nuclear, reticular formation.
[edit] Disorders
The extrapyramidal system can be affected in a number of ways, which are revealed in a range of extrapyramidal symptoms such as akinesia and akathisia.
Extrapyramidal symptoms (EPS) are the various movement disorders such as tardive dyskinesia suffered as a result of taking dopamine antagonists, usually antipsychotic (neuroleptic) drugs, which are often used to control psychosis, especially schizophrenia. Other antidopaminergic drugs like the antiemetic metoclopramide or the tricyclic antidepressant amoxapine can also cause extrapyramidal side effects.
The best known EPS is tardive dyskinesia (involuntary, irregular muscle movements, usually in the face). Other common EPS include akathisia (restlessness), dystonia (muscular spasms of neck - torticollis, eyes - oculogyric crisis, tongue, or jaw; more frequent in children), drug-induced parkinsonism (muscle stiffness, shuffling gait, drooling, tremor; more frequent in adults and the elderly),
Anticholinergic drugs are used to control neuroleptic-induced EPS, although akathisia may require beta blockers or even benzodiazepines. If the EPS are induced by a typical antipsychotic, EPS may be reduced by dose titration or by switching to an atypical antipsychotic, such as aripiprazole, ziprasidone, quetiapine, olanzapine, risperidone or clozapine. These medications have a different mode of action which means they are associated with fewer extrapyramidal side effects than "conventional" antipsychotics (chlorpromazine, haloperidol, etc.).
Although Parkinson's Disease is primarily a disease of the nigrostriatal pathway and not the extrapyramidal system, loss of dopaminergic neurons in the substantia nigra leads to dysregulation of the extrapyramidal system. Since this system regulates posture and skeletal muscle tone, a result is the characteristic dyskinesia of Parkinson's.
Extrapyramidal symptoms can also be caused by brain damage, as in athetotic cerebral palsy, which is involuntary writhing movements caused by prenatal or perinatal brain damage.
Commonly used medications for EPS are benztropine (Cogentin), diphenhydramine (Benadryl), and trihexyphenidyl (Artane).
