Easy summary of Extrapyramidal system

Extrapyramidal system

The  extrapyramidal system is a part of the motor system network causing involuntary actions. The system is called extrapyramidal to distinguish it from the tracts of the motor cortex that reach their targets by traveling through the pyramids of the medulla.

Extrapyramidal tracts are chiefly found in the reticular formation of the pons and medulla.

The pyramidal tracts (corticospinal tract and corticobulbar tracts) may directly innervate motor neurons of the spinal cord or brainstem (anterior (ventral) horn cells or certain cranial nerve nuclei), whereas the extrapyramidal system centers on the modulation and regulation (indirect control) of anterior (ventral) horn cells that are 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, the basal ganglia, the cerebellum, the vestibular nuclei, and different sensory areas of the cerebral cortex. All of these regulatory components can be considered part of the extrapyramidal system, in that they modulate motor activity without directly innervating motor neurons.

Compositions of extrapyramidal system :

Cortical area: premotor are (brodman’s area 6)

Subcortical areas : corpus striatum, globus pallidus , red nucleus , reticular formation , vestibular nucleus  and neocerebellum

Tracts of extra pyramidal system :

• rubrospinal tract
• pontine reticulospinal tract
• medullary reticulospinal tract
• lateral vestibulospinal tract
• tectospinal tract

Functions : 

1.      postural adjustments of the body to maintain balance

2.      gross synergistic voluntary movements in group of muscles affecting proximal joints of the limbs

3.      movement preformed unconsciously like swings of arms during walking

4.      regulatory influence over the reflex activities

Effects of lesion of extra-pyramidal system: muscle tone increased (spasticity)

Clinical relevance

Damage to the extrapyramidal system leads to different forms of movement and cognitive disorders. The majority of such movement disorders are classically described as dyskinesia. Different types of dyskinesia include myoclonus, tics, chorea, athetosis and tremors. Injury to the pyramidal system induces paralysis, whereas extrapyramidal tract disorders result in involuntary movements, muscle rigidity and immobility without paralysis. In some cases, both pyramidal and extrapyramidal systems are affected, such as spastic-athetoid cerebral palsy. Disorders which are seen with many types of extrapyramidal disease are:

• Parkinson’s disease, which is linked to dopamine deficiency in the striatum of basal ganglia. It is characterised by rigidity (increased muscle tone), bradykinesia (slowing of movements) and tremors.
• Non-spastic cerebral palsy, which could be dyskinetic or ataxic. It is caused by damage to the nerve cells outside the pyramidal tracts in the basal ganglia or in the cerebellum.
• Huntington’s disease, which is a choreiform disorder. It is caused by the degenerative process in the striatum.

Extrapyramidal symptoms including acute and tardive dyskinesias and dystonic reactions are sometimes serious side effects of antipsychotic and other drugs.