In the spinal cord, sensory pathways and motor pathways help drive sensory and motor oscillations, respectively. Sensory pathways carry impulses from sensory receptors to the brain and spinal cord, while motor pathways carry impulses from the brain and spinal cord to effector muscles
Effector nerves higher activity and lower motor neurons are the two main groups of neurons belonging to the somatic motor pathways.
What is Upper Motor Neuron?
Superficial neurons (superior nerve cells) are located in the cerebral cortex and the brainstem transmits information downward, which activates intrinsic motor neurons and signal to downstream neurons to ultimately contract or relax the muscles.
What is Lower Motor Neuron?
The nerve cell traveling from the spinal cord to the muscle has its cell body in the spinal cord and terminates in the skeletal muscle.
Difference Between Upper and Lower Motor Neurons
| Upper Motor Neuron | Lower Motor Neuron |
| It is entirely located in the central nervous system. | It is either located in the spinal cord grey matter or within the cranial nerve nuclei in the brain stem. |
| Transmits motor impulses from the brain to the synapses of the lower motor neuron. | Collects the transmitted motor impulses from the upper motor neuron and conducts them to the muscles in the body. |
| Cell bodies of upper motor neurons are bigger than lower motor neuron cell bodies. | Cell bodies are comparatively smaller than the upper motor neurons. |
| Classified on the basis of the pathways they are participating in. | Classified on the basis of the type of muscle fibre they innervate. |
| They form synapses with the lower motor neurons. | They form synapses with the muscles in the body. |
| Upper motor neuron lesions produce spastic hyperreflexia and muscle weakness. | Lower motor neuron lesions result in muscular atrophy, flaccid muscle weakness, fasciculation and hyporeflexia. |
