Editing Motor neuron (section)

{{Short description|Nerve cell sending impulse to muscle}}
{{Infobox neuron
|name = Motor neuron
|image = Medulla_oblongata_-_posterior_-_cn_xii_-_very_high_mag.jpg
|caption = [[Micrograph]] of the [[hypoglossal nucleus]] showing motor neurons with their characteristic coarse [[Nissl substance]] ("tigroid" cytoplasm). [[LFB stain|H&E-LFB stain]].
|location = [[Anterior horn of spinal cord|Ventral horn]] of the [[spinal cord]], some [[cranial nerve nuclei]]
|function = Excitatory projection (to [
|neurotransmitter = [[Upper motor neuron|UMN]] to [[Lower motor neuron|LMN]]: [[glutamate]]; [[Lower motor neuron|LMN]] to [[Neuromuscular junction|NMJ]]: [[ACh]]
|morphology = Projection neuron
|afferents = [[Primary motor cortex]] via the [[Corticospinal tract]]
|efferents = [[Muscle fiber]]s and other [[neuron]]s
}}
A '''motor neuron''' (or '''motoneuron'''), also known as '''efferent neuron'''<ref>{{Cite web|date=2019-12-02|title=Afferent vs. Efferent: AP® Psych Crash Course Review {{!}} Albert.io|url=https://www.albert.io/blog/afferent-vs-efferent-whats-the-difference-ap-psychology-crash-course-review/|access-date=2021-04-25|website=Albert Resources|language=en-US}}</ref> is a [[neuron]] whose [[cell body]] is located in the [[motor cortex]], [[brainstem]] or the [[spinal cord]], and whose [[axon]] (fiber) projects to the spinal cord or outside of the spinal cord to directly or indirectly control effector organs, mainly [[muscle]]s and [[gland]]s.<ref>{{Cite book|title=Principles of Anatomy & Physiology|last1=Tortora|first1=Gerard|last2=Derrickson|first2=Bryan|publisher=John Wiley & Sons, Inc.|year=2014|isbn=978-1-118-34500-9|edition=14th|location=New Jersey|pages=[https://archive.org/details/principlesofanat0000tort/page/406 406, 502, 541]|url=https://archive.org/details/principlesofanat0000tort/page/406}}</ref>  There are two types of motor neuron – [[upper motor neuron]]s and [[lower motor neuron]]s. Axons from upper motor neurons synapse onto [[interneuron]]s in the spinal cord and occasionally directly onto lower motor neurons.<ref name="OUP">{{cite book|last1=Pocock|first1=Gillian|last2=Richards|first2=Christopher D.|title=Human physiology : the basis of medicine|date=2006|publisher=Oxford University Press|location=Oxford|isbn=978-0-19-856878-0|pages=151–153|edition=3rd}}</ref> The axons from the lower motor neurons are [[efferent nerve fiber]]s that carry signals from the [[spinal cord]] to the effectors.<ref>Schacter D.L., Gilbert D.T., and Wegner D.M. (2011) Psychology second edition. New York, NY: Worth</ref> Types of lower motor neurons are [[alpha motor neuron]]s, [[beta motor neuron]]s, and [[gamma motor neuron]]s.

A single motor neuron may innervate many [[myocyte|muscle fibres]] and a muscle fibre can undergo many [[action potentials]] in the time taken for a single [[Muscle_contraction|muscle twitch]]. Innervation takes place at a [[neuromuscular junction]] and twitches can become superimposed as a result of [[Muscle_contraction#Gradation_of_skeletal_muscle_contractions|summation]] or a [[tetanic contraction]]. Individual twitches can become indistinguishable, and tension rises smoothly eventually reaching a plateau.<ref name="Russell 2013 946">{{cite book|last=Russell|first=Peter|title=Biology - Exploring the Diversity of Life|year=2013|publisher=Nelson Education|location=Toronto|isbn=978-0-17-665133-6|pages=946}}</ref>

Although the word "motor neuron" suggests that there is a single kind of neuron that controls movement, this is not the case. Indeed, upper and lower motor neurons—which differ greatly in their origins, synapse locations, routes, neurotransmitters, and lesion characteristics—are included in the same classification as "motor neurons." Essentially, motor neurons, also known as motoneurons, are made up of a variety of intricate, finely tuned circuits found throughout the body that innervate effector muscles and glands to enable both voluntary and involuntary motions. Two motor neurons come together to form a two-neuron circuit. While lower motor neurons start in the spinal cord and go to innervate muscles and glands all throughout the body, upper motor neurons originate in the cerebral cortex and travel to the brain stem or spinal cord. It is essential to comprehend the distinctions between upper and lower motor neurons as well as the routes they follow in order to effectively detect these neuronal injuries and localise the lesions. <ref name="P"> "https://www.ncbi.nlm.nih.gov/books/NBK554616/" </ref>