Motoneuron, also known as motor neurons, are a type of cell body located in the brainstem, motor cortex, or spinal cord. Fibers called axons project outwards to the spinal cord can indirectly or directly control muscles, organs, and glands in the body.
The somatic motor system, also known as the voluntary motor system, is responsible for the movement of skeletal muscles and is under conscious control. It allows for a diverse range of activities, from simple actions like lifting a finger to complex sequences such as playing a musical instrument or participating in athletic events.
Overall, the somatic motor system is a complex and integrated system that allows for the precise control and execution of voluntary movements. Dysfunctions or lesions within this system can lead to a range of motor disorders, such as Parkinson’s disease, Huntington’s disease, spinal cord injuries, Ankylosing Spondylitis or various types of paralysis.
As seen in the previous example of motor neurons in our brain, the motor nerves primary requirement is the ability to instantly control requires sensory input needed to move accurately. A single motor neuron cell can control thousands of muscle fibers strands, creating innervation to move single muscles (twitch). Motor cell structures in the spinal cord region are considered part of the central nervous system (CNS) and connect to many functions.[1] These motoneurons transmit signals from our spinal cord to the musculoskeletal system for movements. Understanding how to use human neurons in regenerative medicine helps the Regeneration center develop more effective stem cell therapies for patients dealing with spinal cord injuries, strokes and brain injuries from traumatic events.
Innervation means “to supply nerves” or “to supply with energy” or “to stimulate.” When nerves embed themselves into muscle fiber, they “innervate” the muscle fibers.[2] This event usually occurs in the neuromuscular junctions and can be identified as simple contractions. They are controlling thousands of individual twitches also us to function and execute movement smoothly and efficiently.
Nerve tracts are thick bundles of axons (white matter), these nerve help carry action signals to their effectors. The spinal cord motor nerves carry impulses from many different regions and act as a point of origin for the lower motor cells.[3]
The seven major motor tracts in the spinal cord include:
Dendrites cells are segments of the neuron that receives stimulation needed neurogenesis and for cells to become activated. Dendrites conduct rapid electrical signals to the neuron cell body asking the cell to function in a specific way. Our nervous system is in charge of the body and controls all other vital system’s functions. Dendrites and neural stem cells help coordinate performance with other systems in the body and are quick to meet our body’s needs in less than one second. The central nervous system uses neuron cells to create movement, and neurons in the brain are necessary for their structure and function. One of the most critical structures in a neuron cell is the dendrite.
Neuron cells require stimuli to become active, and Dendrites are the bridge on the neuron that receives the electrical messages. The electric messages come in two primary forms, including excitatory and inhibitory. Excitatory actions and paracrine cell signalling increase the stimulation of a neuron cell, and inhibitory actions help decrease a neuron’s activity. These signals are accumulated in the neuron cell body (soma) after being collected by dendrites. Once dendrites receive these action signals, they will get sent to an area in the soma called the axon hillock. This area would be in the neck part of a cell body. Once neurons receive enough excitatory signals, they become activated and proceed to create more action potential for other cells.[4]
Neurodegenerative disorders are generally characterized as progressive loss of the function and structure neuron cells associated with neuronal cell death (apoptosis). The most common neurodegenerative disorders include: Motor Neuron Disease (MND), Ataxia, Multiple sclerosis , Parkinson’s disease (PD), Alzheimer’s disease (AD), and amyotrophic lateral sclerosis (ALS).
[1] ^ Benkler, Chen, Alison L O’Neil, Susannah Slepian, Fang Qian, Paul H Weinreb, and Lee L Rubin. 2018. Aggregated SOD1 causes selective death of cultured human motor neurons. Scientific reports, no. 1 (November 6). doi:10.1038/s41598-018-34759-z. https://www.ncbi.nlm.nih.gov/pubmed/30401824
[2] ^ Holzbaur, Erika L F. 2004. Motor neurons rely on motor proteins. Trends in cell biology, no. 5. https://www.ncbi.nlm.nih.gov/pubmed/15130579
[3] ^ Sellers, Drew L, Jamie M Bergen, Russell N Johnson, Heidi Back, John M Ravits, Philip J Horner, and Suzie H Pun. 2016. Targeted axonal import (TAxI) peptide delivers functional proteins into spinal cord motor neurons after peripheral administration. Proceedings of the National Academy of Sciences of the United States of America, no. 9 (February 17). doi:10.1073/pnas.1515526113. https://www.ncbi.nlm.nih.gov/pubmed/26888285
[4] ^ Kim, Minkyung, Brielle Bjorke, and Grant S Mastick. 2017. Motor neuron migration and positioning mechanisms: New roles for guidance cues. Seminars in cell & developmental biology (November 14). doi:S1084-9521(17)30465-2. https://www.ncbi.nlm.nih.gov/pubmed/29141180
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