Extrapyramidal system
Encyclopedia
In human anatomy
Human anatomy
Human anatomy is primarily the scientific study of the morphology of the human body. Anatomy is subdivided into gross anatomy and microscopic anatomy. Gross anatomy is the study of anatomical structures that can be seen by the naked eye...

, the extrapyramidal system is a neural network
Neural network
The term neural network was traditionally used to refer to a network or circuit of biological neurons. The modern usage of the term often refers to artificial neural networks, which are composed of artificial neurons or nodes...

 located in the brain
Human brain
The human brain has the same general structure as the brains of other mammals, but is over three times larger than the brain of a typical mammal with an equivalent body size. Estimates for the number of neurons in the human brain range from 80 to 120 billion...

 that is part of the motor system
Motor system
The motor system is the part of the central nervous system that is involved with movement. It consists of the pyramidal and extrapyramidal system....

 involved in the coordination of movement. The system is called "extrapyramidal" to distinguish it from the tracts of the motor cortex that reach their targets by traveling through the "pyramids
Pyramid of medulla oblongata
The anterior or ventral portion of the medulla oblongata is named the pyramid and lies between the anterior median fissure and the antero-lateral sulcus....

" of the medulla
Medulla oblongata
The medulla oblongata is the lower half of the brainstem. In discussions of neurology and similar contexts where no ambiguity will result, it is often referred to as simply the medulla...

. The pyramidal pathways (corticospinal and some corticobulbar tracts) may directly innervate motor neurons of the spinal cord or brainstem (anterior (ventral) horn cells
Anterior horn (spinal cord)
The anterior horn of the spinal cord is the ventral grey matter section of the spinal cord. The anterior horn contains motor neurons that affect the axial muscles while the posterior horn receives information regarding touch and sensation...

 or certain cranial nerve nuclei), whereas the extrapyramidal system centers around the modulation and regulation (indirect control) of anterior (ventral) horn cells.

Extrapyramidal tracts are chiefly found in the reticular formation
Reticular formation
The reticular formation is a part of the brain that is involved in actions such as awaking/sleeping cycle, and filtering incoming stimuli to discriminate irrelevant background stimuli...

 of the pons
Pons
The pons is a structure located on the brain stem, named after the Latin word for "bridge" or the 16th-century Italian anatomist and surgeon Costanzo Varolio . It is superior to the medulla oblongata, inferior to the midbrain, and ventral to the cerebellum. In humans and other bipeds this means it...

 and medulla
Medulla
Medulla refers to the middle of something and derives from the Latin word for marrow. Its anatomical uses include:* Medulla oblongata, a part of the brain stem* Renal medulla, a part of the kidney* Adrenal medulla, a part of the adrenal gland...

, and target neurons in the spinal cord involved in reflexes, locomotion, complex movements, and postural control. These tracts are in turn modulated by various parts of the central nervous system, including the nigrostriatal pathway
Nigrostriatal pathway
The nigrostriatal pathway is a neural pathway that connects the substantia nigra with the striatum. It is one of the four major dopamine pathways in the brain, and is particularly involved in the production of movement, as part of a system called the basal ganglia motor loop.Loss of dopamine...

, the basal ganglia
Basal ganglia
The basal ganglia are a group of nuclei of varied origin in the brains of vertebrates that act as a cohesive functional unit. They are situated at the base of the forebrain and are strongly connected with the cerebral cortex, thalamus and other brain areas...

, the cerebellum
Cerebellum
The cerebellum is a region of the brain that plays an important role in motor control. It may also be involved in some cognitive functions such as attention and language, and in regulating fear and pleasure responses, but its movement-related functions are the most solidly established...

, the vestibular nuclei
Vestibular nuclei
The vestibular nuclei are the cranial nuclei for the vestibular nerve.In Terminologia Anatomica they are grouped in both the pons and medulla.-Subnuclei:There are 4 subnuclei; they are situated at the floor of the fourth ventricle....

, and different sensory areas of the cerebral cortex
Cerebral cortex
The cerebral cortex is a sheet of neural tissue that is outermost to the cerebrum of the mammalian brain. It plays a key role in memory, attention, perceptual awareness, thought, language, and consciousness. It is constituted of up to six horizontal layers, each of which has a different...

. All of these regulatory components can be considered part of the extrapyramidal system, in that they modulate motor activity without directly innervating motor neurons.

See also

  • List of regions in the human brain
  • Extrapyramidal symptoms
    Extrapyramidal symptoms
    The extrapyramidal system can be affected in a number of ways, which are revealed in a range of extrapyramidal symptoms , also known as extrapyramidal side-effects , such as akinesia and akathisia .Extrapyramidal symptoms are various movement disorders such as acute dystonic reactions,...

  • Rabbit syndrome
    Rabbit syndrome
    Rabbit syndrome is a rare form of extrapyramidal side effect of antipsychotic drugs in which perioral tremors occur at a rate of 5 Hz. Rabbit syndrome is characterized by involuntary, fine, rhythmic motions of the mouth along a vertical plane, without involvement of the tongue...

    , a rare extrapyramidal side effect
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