Motor Neurons

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Motor neurons are cells, which are able to coordinate a motoric function of our body by their influence on contraction and relaxation of the muscles. They are also sometimes called efferent neurons, because they lead information from central nervous system to muscles and tell them what to do.

Motor neuron in a spinal cord
Motor neuron

We can divide motorneurons according to the target systems:

  • Somatic motoneurons are connected to the skeletal muscles and their main role is in locomotion. If this type of motoneurons is activated, the muscle contraction occur, but also their relaxation is important, because it leads to the muscle relaxation. The contraction is not the most important thing, because without the relaxation there is no chance to move. All our voluntary movements are coordinated alternating of contraction and relaxation.
  • The second type is the visceral motorneurons. They control viscera, which we can not affect on our own (e.g.: heart, vascular muscles and others).


Lower motorneuron[✎ edit | edit source]

Upper motoneuron[✎ edit | edit source]


Lesions of the motorneurons[✎ edit | edit source]

A lesion of the motoneuron can be on the upper or on the lower part of a system, but the result is similar in both cases - movement disorders. There are few types of a classification and one of them is a division on the positive and the negative symptoms. Another classification is based on on the degree of disability.

  1. positive symptoms – a function is increased: convulsions, muscle spasms;
  2. negative symptoms – a function is decreased: paresis (partial damage of movement ability), plegia (complete lost of movement ability).


  1. monoplegia (monoparesis) – disability of one limb;
  2. hemiplegia (hemiparesis) – disability of right or left part of a body;
  3. paraplegia (paraparesis) – disability of lower limbs;
  4. quadruplegia (quadruparesis) – involvement of all limbs.


Comparison between central and periferal lesion of motorneurons[✎ edit | edit source]

Function Upper motorneuron lesion Lower motorneuron lesion
Movement ability more affected groups of muscles (diffuse damage) affected is just one innervated region
Reflexes increased (the influence of central inhibition is nonfuctional) decreased or disappeared
Muscle tone increased (hypertonia: spasticity or rigidity) decreased (hypotonia)
Trophic muscle atrophy occurs later as a result of an inactivity early muscle atrophy
Patological movements irritative phenomena fasciculations (spontaneous contractions of muscles); fibrilations (spontaneous contractions of a single muscle fiber)



Links[✎ edit | edit source]

Related articles[✎ edit | edit source]

External links[✎ edit | edit source]

Bibliography[✎ edit | edit source]

  • AMBLER, Zdeněk. Základy neurologie. 7th edition. 2011. ISBN 978-80-7262-707-3.