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What is a Motor Nerve?

Motor nerves are made up of motor neurons, which carry signals that cause muscles to contract.
During a reflex test, motor nerves trigger muscles to contract.
Brain damage may cause a disturbance in communicating with motor nerves in the legs resulting in people having difficulty walking.
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  • Written By: Mary McMahon
  • Edited By: O. Wallace
  • Last Modified Date: 29 September 2014
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A motor nerve is a nerve which carries impulses from the central nervous system which trigger muscles to contract. All of the voluntary muscles in the body are controlled with motor nerves, which means that any time someone decides to move, a motor nerve is involved. All vertebrate animals use this highly effective system for controlling their voluntary muscles. Involuntary muscles such as the heart move using a different system.

These nerves are made up of motor neurons, neurons which specialize in carrying signals which will result in muscle contraction. Where a motor nerve meets a muscle, the neuron releases chemicals which stimulate muscle contraction. Once these chemicals are broken down, the muscle relaxes again. Motor nerves only have an excitatory action, meaning that they can only signal contractions, not relaxation of the muscle.

These nerves are among a group of nerves known as efferent nerves because they carry data from the central nervous system to the rest of the body. When information moves in the opposite direction, it is known as afferent. As an example of the difference between these groups of nerves, efferent nerves would carry the signal to tell the muscles of the hand to grip a pot, but afferent nerves would carry the information that the pot is hot and the hand has been burned.

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It is possible to administer medications which interfere with the activity of motor nerves. These drugs are known as muscle relaxants because they make it difficult or impossible for motor nerves to send signals which will cause the muscles to contract, thereby leaving the muscles in a relaxed state. An example of a use for muscle relaxants is a medical procedure in which it is critical for the patient to stay relaxed, such as the insertion of a urinary catheter.

The network of motor nerve pathways in the body allows people to perform a variety of tasks, from simple to complex. Damage to these nerves or to the parts of the brain which communicate with them can lead to difficulty in making movements, or to confused and irregular movements. Some people who experience brain damage, for instance, have difficulty walking in the wake of the damage because the part of their brain which communicates with the motor nerves in the legs has been disturbed. In these cases, they must learn to walk all over again, teaching their brain how to communicate with the motor nerve pathways.

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anon327861
Post 5

It is true that motor nerves can cause your muscles to move?

anon110320
Post 4

@EarlyForest, that would be true.

EarlyForest
Post 3

I am floundering trying to fill out a worksheet on "What Are Motor Nerves" and I could really use some help with this question. It's a true or false:

"Efferent nerve fibers may be described as motor nerve fibers." Does anyone have any idea? Thank you!

yournamehere
Post 2

@gregg1956 -- My dad had a lesion on his motor cortex, specifically affecting his lower motor neurons. Did your Mom's neuropathy come from an upper motor nerve lesion, or was it from something else?

Either way, I really agree with what you're saying -- it truly is a devastating situation both for the person affected by the lesions and neuropathy, and by those who care for them.

I mean, before my dad was diagnosed, if somebody had asked me what do motor nerve cells do, I would have had no idea -- but they really are so essential to a full life.

gregg1956
Post 1

Motor nerve damage can be devastating, as anyone with motor nerve neuropathy can attest to.

My mother had neuropathy in her upper motor neuron cells, and she was in almost constant pain.

I really empathize with anybody going through something like that -- it takes such a toll on your body physically and emotionally, since the things that should be so easy to do -- lifting a pencil, moving your arms, etc. -- are almost impossible when you have damage to your motor nerve cells.

Truly, my empathy to anyone going through this.

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