2-Minute Neuroscience: Motor Neurons

In this video, I discuss upper and lower motor neurons as well as the syndromes (i.e., upper and lower motor neuron syndrome) that occur when a motor neuron is damaged.

TRANSCRIPT:

A motor neuron is a type of neuron that carries information from the brain or spinal cord and is involved in regulating activity in muscles or glands. There are two types of motor neurons: upper motor neurons and lower motor neurons, which interact with one another to cause movement and other responses.

Upper motor neurons originate in multiple areas of the brain and brainstem and carry information about desired movements or other responses in descending tracts like the corticobulbar and corticospinal tracts. Upper motor neurons descend to various levels of the brainstem and spinal cord and form connections with lower motor neurons. Lower motor neurons then influence the activity of muscles or glands. There are three broad categories of lower motor neurons: somatic motor neurons, which extend to skeletal muscle to control movement and muscle tone; special visceral or branchial motor neurons, which supply muscles in the head and neck; and general visceral motor neurons, which are involved in the autonomic nervous system. Somatic motor neurons can be further subdivided into alpha, beta, and gamma motor neurons depending on the type of muscle fiber they supply.

The consequences of upper and lower motor neuron damage are distinct. Symptoms of upper motor neuron damage, which are collectively called upper motor neuron syndrome, can include weakness or paralysis, spasticity, increased muscle tone, over-responsive reflexes, and a positive Babinski sign, which occurs when the bottom of the foot is stroked and---instead of the toes curling down---the big toe extends up and the other toes fan out. Lower motor neuron damage leads to a collection of symptoms known as lower motor neuron syndrome, which may involve weakness or paralysis, decreased or absent muscle tone, decreased or absent reflexes, involuntary muscle twitches, and muscle atrophy.

REFERENCES:

Purves D, Augustine GJ, Fitzpatrick D, Hall WC, Lamantia AS, Mooney RD, Platt ML, White LE, eds. Neuroscience. 6th ed. New York. Sinauer Associates; 2018.

Zayia LC, Tadi P. Neuroanatomy, Motor Neuron. [Updated 2020 Jul 31]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2021 Jan-. Available from: https://www.ncbi.nlm.nih.gov/books/NBK554616/

Видео 2-Minute Neuroscience: Motor Neurons канала Neuroscientifically Challenged