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Neuron motor: Definition, Overview, Structure, Various Types And Its Serious Neurodegenerative Disorders and Lesion.

Neuron motor Definition

Motor neurons are central nervous system cells. In order to regulate their operational output, motor neurons transmit messages to muscle cells and glands. Neuron motor disease may arise if these cells are damaged in any way. This syndrome is characterised by muscle atrophy and motor function decline.

Neuron motor Overview

Neurons are nerve cells that relay data from the brain and the spinal cord to the remaining portion of the body. About 80 billion neurons make up the human brain! Sensory neurons, interneurons, and motor neurons constitute the three types of neurons. 

  • Sensory neurons detect external stimuli and transform them into data which can be interpreted by the remainder of the nervous system. If you put your hand on a burning stove, for instance, sensory neurons register the heat (pain!) and transmit data to the remaining portion of your nervous system.
  • Sensory neurons obtain data, and motor neurons subsequently translate it into muscle and glandular function. Your motor neurons will engage the muscles in your hand in response to inputs from your sense neurons, allowing you to lift your hand away from the burning stove.
  • When sensory and motor neurons are not directly connected, they are connected by interneurons, which transport information between them.

Structure of a  Neuron motor

Neurons are solitary cells. Consequently, they consist of the nucleus, cell membrane, ribosomes, mitochondria, and other fundamental eukaryotic organelles. They do, however, have a lot more intriguing structure than the textbook depiction of a cell!

Dendrites, cell body (soma), and axon make up the three structural components of a motor neuron. They are multipolar in structure because they contain a single axon and several dendrites.

Dendrites

Dendrites are the branch-like projections seen at the neuron’s terminal end. These are the elements responsible for collecting data from neighbouring neurons and transmitting it to the cell body, in which the information is transmitted as well as the cell is triggered. The average number of dendrites per neuron is five to seven, but certain neurons, such as Purkinje neurons in the brain, have nearly a thousand!

Cell Body (Soma)

Within the cell body are the organelles. It is where the bulk of protein synthesis occurs and governs the cell’s functions.

Axon

The axon is a projection from the cell body that may be quite long. It contains a tube or cable-like shape and transmits data from the dendrites to the other end of the cell, known as the axonal ending, via the cell body. The data is subsequently sent to the next cell, which might be another neuron or an effector cell, including a muscle cell.

Each neuron has a single axon, but it may have multiple branches and terminals, allowing it to communicate with a number of cells. The longest axon in the human body is found in the sciatic nerve. These may grow almost a metre long and extend from the bottom of the lumbar spine to the great toe!

The sites at which neurons interact with one another are called synapses. They are the locations where information is transmitted between both the axon terminal and the dendrite.

Certain neurons are furthermore surrounded by a myelin sheath, which shields the cell from external stimulation that might interfere with signal transmission.

Function of a Neuron motor

Certain neurons are furthermore surrounded by a myelin sheath, which shields the cell from external stimulation that might interfere with signal transmission.

Motor neurons rapidly convey electrical information to generate these movements in our cells. Their specific performance is calculated by the placement of the cell body within the nervous system.

 Neuron motor Locations

Everything in the spinal cord, the brain stem, and the motor cortex (a segment of the cerebral cortex) contains motor neuron cell bodies. The motor cortex is responsible for planning and carrying out voluntary actions.

Their projections subsequently extend throughout the whole of the body to link directly or indirectly with effector organs, notably muscles and glands.

 Neuron motor Types

The two types of motor neurons are upper motor neurons and lower motor neurons.

Neuron motor in the Upper Body

Upper and lower motor neurons include the two varieties of motor neurons. Upper motor neurons are neurons that originate in the motor cortex or brain stem of the brain and transmit data from the brain to interneurons and lower motor neurons. They are the main cells that connect the cerebral cortex to the brain stem or spinal cord to initiate conscious bodily movement.

Lower Neuron motor

Lower motor neurons have been situated in the brain stem and spinal cord and are directly accountable for connecting to effector organs such as muscle cells. By accepting information from them, they stimulate higher motor neurons (directly or through interneurons).

There are three kinds of motor neurons: alpha, beta, and gamma.

Alpha motor neurons are responsible for guiding voluntary muscular contractions by activating extrafusal muscle fibres, which comprise the vast portion of muscle tissue.

Compared to alpha and gamma motor neurons, beta motor neurons are less common and less well investigated. However, it is known that they stimulate intrafusal muscle fibres (which are located farther into the muscle).

Through intrafusal fibres, gamma motor neurons control muscle contraction in accordance with external forces. They control the muscle’s stretch response. Consider the knee-jerk reaction.

The patellar reflex, also referred to as the knee-jerk reflex, is a medical examination used by physicians to evaluate the operation of your neurological system.

You can even give it a go. Maintain an upright posture with your legs off the floor. Strike the tendon just under your kneecap with force. Your lower leg should generate a swift motion in an upwards kicking action. This is known as the knee-jerk reaction.

A reflex arc may be seen here. Your quadriceps muscles are somewhat stretched by your patellar tendon as a result of the acute touch. The muscle spindles detect this movement and excite the sensory neurons as a result. Sensory neurons provide messages to the spinal cord, which then sends information to motor neurons.

The quadriceps muscles contract as a response of the motor neurons, resulting in the kicking action. Interneurons aren’t engaged in this case since the sensory and motor neurons are connected directly.

This reaction may indicate nervous system issues caused by illness or injury. If it does not happen correctly (a trait known as Westphal’s sign) or very dramatic.

Disease of the Neuron motor

Motor neuron disorder is a set of neurodegenerative disorders that predominantly damage motor neurons and cause cell death. Amyotrophic lateral sclerosis (ALS), primary lateral sclerosis (PLS), bulbar onset motor neuron disease (MND) or progressive bulbar palsy (PBP), and progressive muscular atrophy are also motor neuron diseases (PMA).

Motor neuron illness causes muscular weakness, stiffness, and loss that the motor neurons can no longer communicate with the muscles effectively. This results in a wide spectrum of symptoms that vary depending on the condition and the person.

The early signs and symptoms of motor neuron illness include muscular weakness as well as possible cognitive and behavioural abnormalities. The condition may interfere with a person’s ability to eat, drink, speak, move, and breathe. Most people who are impacted will eventually lose their capacity to do these duties completely.

The most frequent kind of motor neuron disease is ALS, widely called Lou Gehrig’s disease. Stephen Hawking and Christopher Reeve are two famous people who died as a consequence of complications from the disease. The “Ice Bucket Challenge,” a viral video craze that began in 2014, raised awareness of the illness and raised funds for research.

The exact aetiology of motor neuron illness is uncertain. The condition is likely to be caused by a combination of genetic and environmental causes, with a family relationship sometimes present. Mutations in the C21orf2 gene have been found in studies and are considered to be associated with certain instances of ALS.

Upper  Neuron motor Lesion

Impairment to the motor neurons of the brain or brain stem which project to the spinal cord is described as an upper motor neuron lesion, sometimes called pyramidal insufficiency. Multiple sclerosis (MS), stroke, brain damage, and cerebral palsy are only a few of the conditions that may cause such damage.

Upper motor neuron disease is the name given to the signs that occur (UMND). Muscle weakness, poor motor control, bad posture, and excessive reflex reactions are all signs.

Lower  Neuron motor Lesion

Lower motor neuron lesions refer to the deterioration of the motor neurons that connect the spinal cord to the effector muscles. Muscle paralysis and weakness are prevalent indicators, and the lesions are often the result of a systemic infection such as Lyme disease, HIV, or the Herpes virus (which may result in Bell palsy).

References

Stifani, & Nicolas. (2014). Motor neurons and the generation of spinal motor neurons diversity. Retrieved from https://www.frontiersin.org/articles/10.3389/fncel.2014.00293/full

Manuel, M., & Zytnicki, D. (2011). Alpha, beta and gamma motoneurons: functional diversity in the motor system’s final pathway. Retrieved from https://www.ncbi.nlm.nih.gov/pubmed/21960303

Lodish H, Berk A, Zipursky SL, et al. Molecular Cell Biology. 4th edition. New York: W. H. Freeman; 2000. Section 21.1, Overview of Neuron Structure and Function. Available from: https://www.ncbi.nlm.nih.gov/books/NBK21535/

MND Association – Supporting people affected by MND. Retrieved from https://www.mndassociation.org/

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