A form of motor neuron whose cell body is situated in the motor area of cerebral cortex is called the UMN (Upper Motor Neuron). The processes of these Neurons are connected with nuclei of the motor in anterior horn of spinal cord or in the brain stem of spinal cord. These neurons are responsible for carrying information from the brain to specific muscles. The UMN (Upper Motor Neurons) are used for connection of the brain with some level of spinal cord. These signals are sent to portions of body by help of other neurons which help different body parts to function properly after being interpreted by the receptors inside the body.
Spinal and Cranial nerves are referred to as LMN whose cell body is situated in areas of the main brain stem. These neurons are allowed to go from brain system of body and can pass a chemical signal to some other part of the body such as muscles or neurons. LMN are nerves which are either spinal or cranial. The spinal nerves have a component of Lower Motor Neuron as they are mixed nerves. Not all the nerves in cranial part of the body system are components of these LMN.
Failure of working of any of these motor neuron systems or any damage to the path of these motor neurons cause a group of symptoms which are called as syndrome. The problems are mostly caused in these motor neuron systems as a result of some injury and the issues associated with UMN and LMN can be classified by different signs and symptoms which include problems in reflexes and also improper functioning and occurrence of fine movement in different parts of body. The working of these motor neuron systems are linked with each other. When signals are formed and passed on from Upper Motor Neuron, they enter in to Lower Motor Neuron system from where they are further communicated to the parts of body where certain action is to be performed.
Difference between UMN and LMN
UMN are generated in the region of Cerebral Cortex of Brain and the information is then carried on to different parts of the body. LMN, on the other hand are placed lowest in the Motor System which allows them to receive inputs from higher portion of the neuron system. The UMN are distributed in systems such as extra pyramidal and Pyramidal systems. On the other hand, LMN can be found in some of the Horn Cells and neurons which are related to the Anterior Horn Cells in some of the cranial nerves. The UMN are systems which are used for connection of brain with spinal cord through which signals pass to different muscles. The LMN receive these signals from UMN and pass them on to other parts of the body. The LMN are responsible to provide signals to muscle fibers allowing the muscles to function according to the instructions provided by the nervous system. LMN are based on two different types of Neurons as compared to the UMN which are of a single type only.