Difference Between Upper and Lower Motor Neurons

Upper vs Lower Motor Neurons

A neuron is a brain cell that processes and transmits information by chemical and electrical signalling. It is a component of the nervous system. It is comprised of a cell body, axon, and dendrites. A neuron maintains a voltage gradient on the membrane by ion pumps which work by combining with ion channels to generate intracellular-versus-extracellular concentration differences of ions like potassium and sodium. A motor neuron is a neuron that stems off from the spinal cord. It projects its axons outside of the spinal cord and controls muscles directly or indirectly.

Upper motor neurons originate in the motor region of the brain stem. They are not responsible for the stimulation of the muscle which is targeted as they do not carry information down to the final common pathway. They work through a neurotransmitter called glutamate which transmits the nerve impulses from upper to lower motor neurons where it is detected by glutamatergic receptors. On the other hand, lower motor neurons receive impulses from the upper motor neurons and connect the spinal cord and brain stem to the muscle fibers. They are the cranial and spinal nerves. They work by making use of the glutamate which is released from the upper motor neurons, and this triggers depolarization in the lower motor neurons. A series of actions occur which end up signalling the muscle to contract. The cell bodies of the lower motor neurons are located in the neuraxis, and their axons leave and synapse with the muscles in the body. On the other hand, the upper motor neurons synapse with the lower motor neurons as they are unable to leave the central nervous system.

Summary

1.Cell bodies of the upper motor neurons are bigger in size than cell bodies of the lower neurons.
2.Upper motor neurons are classified according to the pathways they travel in. Lower motor neurons are classified according to the type of muscle fiber they innervate as they have only one path which is called the final common pathway. Upper motor neurons have six pathways. Lower motor neurons are divided into two groups, the alpha and gamma motor neurons.
3.Upper motor neurons carry information from brain centers that control the muscles of the body, and lower motor neurons carry information passed to them from the upper motor neurons.
4.Upper motor neurons form synapses with the lower motor neurons. On the other hand, lower motor neurons form synapses with the muscles in the body.
5.Upper motor neurons are first-order neurons whilst lower motor neurons are second-order neurons.
6.The cell bodies of the upper motor neurons are located in the cortex of the brain and the cell bodies of the lower motor neurons are located in the grey matter of the spinal cord and brain stem.

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