Neurons are a fundamental part of the basic human body. Upper motor neuron lesions are just another name given to UML. They are commonly known as upper motor neurons. UML are neurons in the brain and spinal cord that have been damaged. Lower motor neuron lesions are another name for LMN.
Upper Motor Neuron vs Lower Motor Neuron
The main difference between Upper Motor Neuron and Lower Motor Neuron is that upper motor neurons or UMN are Lesions of the neurons in the spinal cord and the brain. Whereas Lesions of cranial and spinal motor neurons that directly innervate the muscles are known as lower motor neurons.
In the upper motor neuron, there will be hypertonia, hyperreflexia, and spasticity. So if there is damage to UMN there will be a loss of control to LMN because LMN or Lower motor neurons are controlled by UMN or upper motor neuron. it causes an increase in Tonia, an increase in reflexes, and spasticity.
In lower motor neurons there will be hypotonia, hypo-relexia, flaccidity. Here also there will be atrophy but it is due to denervation(loss of nerve supply) of motor nerve muscles. Additionally, in Lower motor neuron lesions there will be a fasciculation that is the spontaneous contraction of small muscle fibers because of stimulation of few single muscle fibers.
Comparison Table between Upper Motor Neuron and Lower Motor Neuron.
| Parameters of Comparison | Upper Motor Neuron | Lower Motor Neuron |
| Muscle weakness | In UMN it can be Quadriplegia, Hemiplegia, paraplegia and Diplegia. | In LMN it can be of two types: if it involves muscles |
| Muscle tone | Depending on muscle tone it can be spasticity and rigidity. | LMN having Hypotonia means an abnormally low level of muscle tone. |
| Fasciculations | In UMN it is absent | In LMN it is present |
| Tendon Reflexes | In UMN it is hyperreflexia | In LMN there will be hypo/Areflexia |
| EMG(electromyography) Analysis. | Normal nerve conduction. | Abnormal nerve conduction. |
What is Upper Motor Neuron?
The body part upper motor neuron was first given in 1886 by William Gowers. The upper motor neuron or UML is present in the cerebral cortex brain stem. The upper motor neurons or UML are the primary source of voluntary movement and are present in the cerebral cortex. UMN carries information down to inter motor neurons and lower motor neurons.
Upper motor neurons control the lower motor neuron. The cerebral cortex contains pyramidal cells, including a kind of gigantic pyramidal cell known as Betz cells. Betz cells are the biggest cell bodies in the brain, with a diameter of 0.1mm. Upper motor neuron refers to the pyramidal cells of the precentral gyrus. In the spinal cord root, the top motor neuron descends.
In the neural passage which is present above the anterior horn of the spinal cord. any UMN injury is known as pyramidal insufficiency, occurs. Upper motor neurons pass through the central nervous system through numerous neural routes. If there is an injury to UMN or Upper motor neuron then it could result in exaggerated and spasticity reflexes. Upper motor neuron lesion affects a group of muscles and does not serve as muscle atrophy. Hyperactive deep reflex and Babinski sign becomes negative.
What is Lower Motor Neuron?
The higher motor neuron will connect with the LMN present at the interior side of the spinal cord once it reaches the right spinal level. The lower motor neuron focuses on the muscles that control the movement of the bodily part in question. The lower motor neuron is found at either the cranial nerve nuclei of the brainstem or anterior grey column and motor function with cranial nerves.
Lower motor neurons start to activate towards the bottom mean from the spinal cord. Lower motor neurons carry signals to muscles for the contract. The fibers which come from the cranial nerve are considered lower motor neurons. The lower motor neurons act into muscles. Lower motor neuron connected to upper motor neuron so supposes if the upper motor neuron gets removed lower motor neuron works freely and targets muscles and increases its activity power more.
But if the lower motor neuron gets removed the Upper motor neuron muscles get flaccid paralysis. So ultimately if lower motor neurons go there will be a lot of loss we suffer. Lower motor neuron works for only single muscles. In lower motor neuron reflexes are lost and the Babinski sign is positive.
Main Differences Between Upper Motor Neuron And Lower Motor Neuron
- The UMN or upper motor neurons are found in the area of the cerebral cortex of the brain while LMN or lower motor neuron are there in the spinal cord.
- The Upper Motor Neuron carries information on the different parts of the body while Lower Motor Neuron allows it to receive inputs from the higher portion of the neuron system.
- The Upper Motor Neuron is used to pass signals to the different muscles while the Lower Motor Neuron received that signal and passed it to the other parts of the body.
- The Upper Motor Neuron is based on only one type of neuron while Lower Motor Neuron is based on two different types of neuron.
- The Upper Motor Neuron is distributed in the pyramidal system while the LMN is found in the cranial nerves and anterior horn cells.
Conclusion
Simply, we understand as much about UMN and LMN and the term Lesions. The specific term or word which is used in some lines all are biological terms so there is no such specific meaning of it. But I tried my best to explain a whole about upper motor neurons and lower motor neurons with their differences. And by reading this you also got some idea of how to prevent the diseases which occur by upper motor neuron and lower motor neuron. Here we Simply understand and explore more on the neuron part so by reading this full article you get as much knowledge about these two important terms.
References
- https://n.neurology.org/content/68/19/1571.short
- https://www.sciencedirect.com/science/article/pii/S1388245706001143