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.
Reflex activities of a target muscle are affected by motor signals from the corticospinal tract and by the influence of extrapyramidal signals.
Disorders of the extrapyramidal system
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 side effects (EPS) are the various movement disorders suffered as a result of taking antipsychotic (neuroleptic) drugs, which are often used to control psychosis, especially schizophrenia.
Common EPS are 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), and tardive dyskinesia (involuntary, irregular muscle movements, usually in the face).
Anticholinergic drugs are used to control neuroleptic-induced EPS, although akathisia may require beta blockers or even benzodiazepines. They can also be reduced by dose titration or by use of an atypical antipsychotic, such as olanzapine, risperidone, quetiapine or clozapine. These medications have a different mode of action which means they are associated with fewer extrapyramidal side effects that "conventional" antipsychotics (chlorpromazine, haloperidol, etc.).
Commonly used medications for EPS are benztropine (Cogentin), diphenhydramine (Benadryl), and trihexyphenidyl (Artane).
See also: List of regions in the human brain