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To know the difference between upper and lower motor neurons, let’s get introduced to these terms.

To know the difference between upper and lower motor neurons, let’s get introduced to these terms. The Central Nervous system (CNS) consists of the brain in the spinal cord and upper motor neurons are higher up in the CNS whereas lower motor neurons are located at the lower regions of the CNS. Also known as motoneuron, motor neuron is the neuron having cell body located in the motor cortex, spinal cord or the brainstem, and whose axon fiber projects to the spinal cord or outside of the spinal cord (to directly/indirectly controlling effector organs like muscles and glands. Spinal cord is the place where a communication between upper and lower motor neurons takes place.

Upper motor neurons (upper nerve cells) are present in the cerebral cortex and also brainstem carry information down to activate interneurons and also lower motor neurons which ultimately signal muscles to contract or relax.

It is the nerve cell that goes from the spinal cord to the muscle  Its cell body is in the spinal cord and its termination takes place in a skeletal muscle. (Image to be added soon) Let’s see at the below tabular chart to know the upper motor neuron vs lower motor neuron.

The difference between upper and lower motor neuron lesion is such that an upper motor neuron lesion is the lesion that occurs in the neural pathway above the anterior horn of the spinal cord or cranial nerves motor nuclei; whereas a lower motor neuron lesion affects the nerve fibers that travel from the anterior horn of the spinal cord to the associated muscle.

The upper motor neuron is found in the cerebral cortex and also brainstem. It carries information down for activating interneurons and lower motor neurons, which directly signal muscles to relax or contract. The spinal cord is the region for communication between the upper motor neuron and the lower motor neuron. Any lesion above the spinal cord will result in UMN syndrome and at this point and below are associated with LMN.

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These are the neurons located within the brain or brainstem. Innervates Alpha and Gamma motor neurons in ventral horn

These are the alpha and gamma motor neurons located in the ventral horn of the spinal cord.

Axon travels peripherally to innervate muscle.

It is the motor system restricted to the Central Nervous System.  Upper motor neuron is responsible for effectively managing voluntary movement, maintenance of muscle tone for supporting the body against gravity and also provides regulation of postures to provide a stable background upon which it is needed to initiate the voluntary activity.

It is the efferent neuron of the peripheral nervous system (PNS) that connects the CNS with the muscle to be innervated. It is the nerve cell present in the spinal cord and its termination being in skeletal muscle.

UMNs have numerous regulatory functions. They can modulate the activity of α- and γ-LMNs either directly (mono synaptically) or indirectly (via interneurons).

The entire function of the CNS is manifested through this neuron.

The cell bodies of the upper motor neuron are bigger as compared to the lower motor neuron cell bodies.

The cell bodies of the lower motor neurons are comparatively smaller.

These transmit motor impulses from the brain to the synapses of the lower motor neuron.

These neurons collect the transmitted motor impulses from the upper motor neuron to the muscles in the body.

Diseases related with its dysfunction include spinal cord injury, multiple sclerosis and stroke. A motor neuron disease where only the upper motor neuron is affected is primary lateral sclerosis.

Its loss leads to body weakness, fasciculation or twitching of muscle and loss of muscle mass called muscle atrophy.

The diseases associated with upper motor neurons are a heterogenous group of disorders in which a degeneration of motor neurons of the cortex and tronco encefalico motor nucleus occurs. Symptoms include weakness, spasticity, motor clumsiness and hyperreflexia.

The General Somatic Efferent fibers present here involve all neurons that innervate striated voluntary skeletal muscle (which is derived from somites and somatic mesoderm in the limb buds of the wall and from somitomeres in the head). The lower motor neurons are located in all of the spinal nerves and all of the cranial nerves except I, II and VIII.

These are classified based on the pathways they travel.

Their classification is based on the muscle fibre type they innervate.

These form synapses with the lower motor neurons.

These form synapses with the muscles in the body.