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Upper motor neuron | lower mother neuron | Paralysis

UPPER MOTOR NEURON AND
 LOWER MOTOR NEURON


Neurons of the motor system are divided into      a. upper motor neurons and
b. lower motor neurons,
(depending upon their location and termination.)

Upper Motor Neuron

Upper motor neurons are the neurons in higher centers of brain, which control the lower motor neurons.
Upper motor neurons are of three types:

 1. Motor neurons in cerebral cortex. 

Fibers of these neurons form corticospinal (pyramidal) and corticobulbar tracts.

 2. Neurons in basal ganglia and brainstem nuclei

3. Neurons in cerebellum.

Motor neurons in cerebral cortex, which give origin to pyramidal tracts belong to the pyramidal system and the remaining motor neurons belong to extrapyramidal system.

Some controversy exists in including the neurons of extrapyramidal system under the category of upper motor neurons. However, considering in terms of the definition, neurons other than lower motor neurons are
to be named as upper motor neurons.

Lower Motor Neuron


 Lower motor neurons are the anterior gray horn cells in spinal cord and motor neurons of cranial nerve nuclei, situated in brainstem, which innervate the muscles directly.
Thus, the lower motor neurons constitute ‘final
common pathway’ of motor system.

 Lower motor neurons are under the influence of upper motor neurons.

 Effects of Motor Neuron Lesions

Effects of lower motor neuron lesion are the loss of muscle tone and flaccid paralysis.
Effects of upper motor neuron lesion depends
upon the type of neuron involved.

 Effects of upper motor neuron lesion are:

 1. Lesion in pyramidal system causes hypertonia and spastic paralysis.
Spastic paralysis involves only one group of muscles, particularly the extensor muscles.

2. Lesion in basal ganglia produces hypertonia and rigidity involving both flexor and extensor muscles

3. Lesion in cerebellum causes hypotonia, muscular weakness and incoordination of movements.

Paralysis

 Paralysis is defined as the complete loss of strength and functions of muscle group or a limb.

Causes for paralysis
Common causes for paralysis are -
-trauma,
-tumor,
-stroke,
-cerebral palsy (condition caused by brain injury
immediately after birth),
-multiple sclerosis,
-neurodegenerative diseases.

 Types of paralysis

Paralysis of muscles in the body depends upon type and location of motor neurons affected by the lesion.


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