Chapters 5 - Motor systems 03. The extrapyramidal system

03. The extrapyramidal system

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"In Spite of the great degree of motor weakness and helplessness, in a pure case [of hepatolenticular degeneration] the abdominal reflexes are preserved and has dual flexor response is Obtained ... in other words, this affection, Where It OCCURS in an uncomplicated form, is an extrapyramidal motor disease "Kinnier Wilson (1912).

Next to the pyramidal tract, there are many ways and circuits involved in involuntary motor skills (including posture and balance) in the automation of gestures and movement coordination.

These pathways are very complex because they involve several components of the nervous system: cerebral cortex, cerebellum, basal ganglia, brainstem and spinal cord. They therefore have a lot of very difficult to study nervous relay.

1. Definition:

The term extrapyramidal a problem of terminology. Indeed, we must distinguish between two uses for the term: The extrapyramidal system often refers to engine system governed by the basal ganglia [ 79 ], and extrapyramidal pathways that involve the descending motor pathways in the spinal cord independently the pyramidal pathway.

2. Extrapyramidal system:

The concept of the extrapyramidal system [ 75 ] was introduced in 1912 by Kinnier Wilson [ 158 ]. It was thought that there was a separate entity that regulates the motor next to the pyramidal tract.

It turned out again later that this system is so complicated that the concept (extrapyramidal) itself begins to lose some of its interest in the field of neurological physiology [ 4 ] in favor of the concept of system basal ganglia [ 158 ], but it retains its importance in the field of neurological disease [ 91 ]. Indeed, the damage of each core that occurs in this system causes the appearance of specific motor abnormalities [ 41 ].

Extrapyramidal system involves the basal ganglia [ 38 , 39 , 78 , 79 ]. This is a system of control of voluntary movement. When motion is initiated by the pyramidal system, collateral will leave to the basal ganglia to inform the extrapyramidal system of the nature of the movement to achieve [ 41 ].

The system will analyze the target and provide a neurological movement scenario (series of excitations and inhibitions of pyramidal neurons of the primary motor cortex) to achieve the movement of the most appropriate and most fluidly.

The extrapyramidal system has no direct motive extension to the spinal cord. This is a system that has a large number of circuits that involve several types of feedback to work, but the result of this analysis always ends on the primary motor cortex to control movement [ 41 ].

3. Extrapyramidal pathways:

Extrapyramidal pathways consist of four main clusters:

  • The rubrospinal beam [ 38 , 41 ], which share the red nucleus and follows a path parallel to the lateral corticospinal tract. It is involved in motility and coordination of large distal muscles of upper and lower limbs. The red nucleus is linked to cerebellar system and receives no afferent system of the basal ganglia [ 31 ].
  • The vestibulo-spinal tract [ 3 ] is involved in the control of balance.
  • The reticulo-spinal tract [ 41 ] plays a role in muscle tone, walking and automatic postural adjustments.
  • The spinal colliculo beam (spinal or tectonic) [ 38 ] connects the midbrain tectum with the spinal cord. It controls the movements of the head in response to visual and auditory stimuli.

Chapters 5 - Motor systems 03. The extrapyramidal system