Extra pyramidal motor system
The extrapyramidal motor system ( EPMS ) or extrapyramidal system ( EPS ) for short is a neuroanatomical and physiological concept in which all movement control processes ( motor functions ) are found that do not run along the pyramidal trajectory of the pyramidal system .
This concept is only useful in primates , especially in humans , since the pyramidal system is only of great importance and a certain dominance in movement control with them. In other mammals , virtually all motor control is extrapyramidal. After all, the other vertebrates have no pyramidal system at all.
There is actually no clear functional separation between pyramidal and extrapyramidal systems. That is why it is repeatedly asked to reject this concept. However, the distinction is helpful in understanding neurological disease patterns.
Layout and function
The extrapyramidal motor system has its origin in the motor cortex ( Brodmann areas 6 and 8 = areas extrapyramidal ) as well as in numerous other core areas of the brain. Its most important component are the basal ganglia . It primarily controls the seemingly coarser movement sequences, especially of the trunk (tonic holding and support motor skills) and proximal extremity muscles (so-called mass movements) and thus represents the basis for the pyramidal interconnected fine motor skills. Furthermore, the EPS strongly influences the muscle tone (rubrospinal tracts) and through the interconnection with the cerebellum , the optical reflex center and the equilibrium nuclei , it also ensures the harmony of movements and the correction of posture.
The representation of the EPS as an efferent system excluding the involuntary, coarse supporting and holding movements, which is contrasted with the pyramidal system, is considered incorrect and obsolete. The two systems are to be regarded as synergistic.
The extrapyramidal motor system is polysynaptic, so it always has several switching points ( synapses ). Switching takes place in the nuclei of numerous brain areas. The most important stations in the extrapyramidal system are the nucleus ruber and the formatio reticularis , as only these go directly to the upper (first / central) motor neuron. The most important neurotransmitter in EPS is dopamine .
Damage to the extrapyramidal system
In humans, lesions are predominantly of the EPS by eliminating the inhibitory ( inhibitory ) influences on the upper motoneuron (UMN) in ( extrapyramidal syndrome or Extrapyramidalmotorisches syndrome (EPMS)). This leads to diseases with greatly increased movement sequences such as Huntington 's disease or strongly inhibited movement sequences such as Parkinson's disease . In addition, in the case of EPS damage, reflexes can be increased due to the lack of inhibitory effect of inhibitory interneurons on the UMN ( hyperreflexia ). In non- primates , hemipareses usually occur with impaired posture and postural reactions . However, if the damage is in front of the ruber nucleus , movement disorders rarely occur.
A spinal cord injury with paraplegia usually also results in damage to the extrapyramidal pathways in the spinal cord. Since the pyramidal pathways are impaired at the same time , the muscle no longer receives calming impulses and the tone or the tone-enhancing reflex arc from the spinal cord can prevail. The result is often spasticity .