Motor nerve

Motor nerve fibers transduce signals from the CNS to peripheral neurons of proximal muscle tissue. Motor nerve axon terminals innervate skeletal and smooth muscle, as they are heavily involved in muscle control. Motor nerves tend to be rich in acetylcholine vesicles because the motor nerve, a bundle of motor nerve axons that deliver motor signals and signal for movement and motor control.{{Cite book|title=Neuroscience 5th Edition|last=Purves|first=Dale|publisher=Sunderland, Mass|year=2012}} Calcium vesicles reside in the axon terminals of the motor nerve bundles. The high calcium concentration outside of presynaptic motor nerves increases the size of end-plate potentials (EPPs).{{Cite journal|last1=Jang|first1=Sung Ho|last2=Lee|first2=Han Do|date=December 2017|title=Gait recovery by activation of the unaffected corticoreticulospinal tract in a stroke patient: A case report|journal=Medicine|language=en-US|volume=96|issue=50|pages=e9123|doi=10.1097/MD.0000000000009123|pmid=29390312|pmc=5815724|issn=0025-7974}}

Within motor nerves, each axon is wrapped by the endoneurium, which is a layer of connective tissue that surrounds the myelin sheath. Bundles of axons are called fascicles, which are wrapped in perineurium. All of the fascicles wrapped in the perineurium are wound together and wrapped by a final layer of connective tissue known as the epineurium. These protective tissues defend nerves from injury, pathogens and help to maintain nerve function. Layers of connective tissue maintain the rate at which nerves conduct action potentials.{{Cite book|title=Textbook of medical physiology|last=C.|first=Guyton, Arthur|date=2006|publisher=Elsevier Saunders|others=Hall, John E. (John Edward), 1946-|isbn=978-0721602400|edition=11th|location=Philadelphia|oclc=56661571}}

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Most motor pathways originate in the motor cortex of the brain. Signals run down the brainstem and spinal cord ipsilaterally, on the same side, and exit the spinal cord at the ventral horn of the spinal cord on either side. Motor nerves communicate with the muscle cells they innervate through motor neurons once they exit the spinal cord.

Motor nerves can vary based on the subtype of motor neuron they are associate with.{{Cite book|title=Gray's anatomy|author=Gray, Henry|date=1989|publisher=C. Livingstone|others=Williams, Peter L. (Peter Llewellyn), Gray, Henry, 1825-1861.|isbn=978-0443041778|edition=37th |location=Edinburgh|oclc=18350581}}

Alpha motor neurons target extrafusal muscle fibers. The motor nerves associated with these neurons innervate extrafusal fibers and are responsible for muscle contraction. These nerve fibers have the largest diameter of the motor neurons and require the highest conduction velocity of the three types.

Beta motor neurons innervate intrafusal fibers of muscle spindles. These nerves are responsible for signaling slow twitch muscle fibers.

Gamma motor neurons, unlike alpha motor neurons, are not directly involved in muscle contraction. The nerves associated with these neurons do not send signals that directly adjust the shortening or lengthening of muscle fibers. However, these nerves are important in keeping muscle spindles taut.

Motor neural degeneration is the progressive weakening of neural tissues and connections in the nervous system. Muscles begin to weaken as there are no longer any motor nerves or pathways that allows for muscle innervation. Motor neuron diseases can be viral, genetic or be a result of environmental factors. The exact causes remain unclear, however many experts believe that toxic and environmental factors play a large role.{{Cite news|url=https://www.medicalnewstoday.com/articles/164342.php|title=Motor Neuron Disease}}

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There are problems with neuroregeneration due to many sources, both internal and external. There is a weak regenerative ability of nerves and new nerve cells cannot simply be made. The outside environment can also play a role in nerve regeneration. Neural stem cells (NSCs), however, are able to differentiate into many different types of nerve cells. This is one way that nerves can "repair" themselves. NSC transplant into damaged areas usually leads to the cells differentiating into astrocytes which assists the surrounding neurons. Schwann cells have the ability to regenerate, but the capacity that these cells can repair nerve cells declines as time goes on as well as distance the Schwann cells are from site of damage.{{Cite news|url=https://www.columbianeurosurgery.org/conditions/peripheral-nerve-disorders|title=Peripheral Nerve Disorders - Columbia Neurosurgery|work=Columbia Neurosurgery|access-date=2018-03-26|language=en-US}}{{Cite journal|date=2016-05-01|title=Nerve Regeneration: Understanding Biology and Its Influence on Return of Function After Nerve Transfers|journal=Hand Clinics|language=en|volume=32|issue=2|pages=103–117|doi=10.1016/j.hcl.2015.12.001|pmid=27094884|issn=0749-0712|last1=Gordon|first1=Tessa}}{{Cite journal|last1=Huang|first1=Lixiang|last2=Wang|first2=Gan|date=2017|title=The Effects of Different Factors on the Behavior of Neural Stem Cells|journal=Stem Cells International|language=en|volume=2017|pages=9497325|doi=10.1155/2017/9497325|pmid=29358957|pmc=5735681|issn=1687-966X|doi-access=free}}{{Cite news|url=https://orthoinfo.aaos.org/en/diseases--conditions/nerve-injuries/|title=Nerve Injuries - OrthoInfo - AAOS|access-date=2018-03-26}}

• Sensory nerve
• Afferent nerve fiber
• Efferent nerve fiber
• Sensory neuron
• Motor neuron (efferent neuron)

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{{Nervous tissue}}

Category:Nervous system