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My professor says

Nervus troclearis IV somatomotor fibers supply musculus obliquus superior.

and similarly for nervus oculomotorius III

Nervus oculomotorius postganglionic fibers supply musculus ciliaris, m. sphincter pupillae.

I understand the verb "supply" as "stimulate" or "allow signal pass from the tract to the muscle that contracts or flexes". However, fibers must have some other functions too. So the verb supply seems to be a general term for these functions.

How do fibers control the muscle?

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I'm of the opinion that this question is either too localised or even off-topic in its present form. Perhaps consider rewording it to sound less like a use of english question - "what is the link between these nerves and muscles" or similar? –  Rory M Mar 30 '12 at 16:59
    
I guess that was partly my fault from my edit. –  Daniel Standage Mar 30 '12 at 17:07
    
@DanielStandage I wouldn't say that :) Anyway it's in better shape now, I've reversed my down-vote. –  Rory M Mar 30 '12 at 17:16
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I still think it needs more explanation. Are you looking for the answer to how action potentials are carried along motor neurons or how neuromuscular junctions work or both of the above? –  kmm Mar 30 '12 at 21:23
    
@Kevin so the thing includes the two things. I know about the first one that myelin is used in some cases as a resistant. I know about the last one that there are transmitter substances like acetylcholine that is released from the end of the axon to the extracellular space that activates the action potential in some other cells by attaching to receptors of other cells. So there is a synapse going on between neurons. - Those things should apparently apply to the above examples. However, not sure how m. ciliaris is in connection with m. sphincter pupillae. Fibers activating muscles in sequence? –  Masi Mar 30 '12 at 22:19
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1 Answer

up vote 5 down vote accepted

Read "supply" as "carry action potentials to." When the action potential reaches the junction with the muscle (i.e., the neuromuscular junction), neurotransmitters are released into synapse. A similar membrane depolarization occurs on the muscle cell, ultimately leading to contraction.

Nerves visible to the naked eye are actually bundles of individual axons (hundreds, thousands, or tens of thousands of axons). Nerves have the appearance of branching because the individual axons that travel to muscle fibers don't all go to one muscle.

For example the oculomotor nerve branches:

Oculomotor nerve

So what you see as the oculomotor nerve is really a collection of neurons. Some of these carry action potentials to the ciliary muscle and some to the sphincter pupillae. These are the parasympathetic components. There is a completely separate set of neurons (but still contained in the same nerve) that carry signals to the extraocular muscles.

This is really basic material that your professor should have explained to you.

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Can you distinct the parasympathetic components of the nervus oculomotorius from a picture by eye? –  Masi Mar 31 '12 at 10:02
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They would be indistinguishable to the naked eye. You could only tell the divisions by where the (very tiny) branches go to. –  kmm Mar 31 '12 at 15:35
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