Does CNS in spine have single fiber per inervated muscle?

[cave_cat]

if I can move specific muscle in my toe via brain command, does this mean that in spinal cord there is a specific fiber that extends from brain to that toe? And let's say if in a lab rat we cut that single CNS fiber, the muscle affected will stop working without any other consequences to the organism?

Or is this mental model in fact completely wrong so that let's say CNS does time domain multiplexing (or packet addressing? or some other form of multiplexing?), allowing it to send commands to multiple muscles through a single "cable" / fiber?

 

[cave_cat]

roughly the same question has been asked here http://biology.stackexchange.com/qu...ormation-sent-from-limbs-to-the-brain-exactly

AFAICT people responding did not explain how the spine does addressing / routing / multiplexing of messages between the muscle and the corresponding brain sector (microcolumn? whatever). Oh well.

 

[bobze]

There is not a single neuron that goes from the brain to the toe. There is however a group of connected neurons that travel this path. For muscle innervation it's pretty straightforward 1:1 type connections. It gets more tricky for sensory input where you do have "packet addressing". In fact we get errors in addressing sensory information. Probably the easiest example is with referred pain and the best example of that is wit heart attacks (easy to Google). Can't elaborate more right now I'm on my phone and I hate typing on phones!

 

[Danger]

In reference to the specific wording of the original post, it partially depends upon the species. A horse, for instance, has sort of a "second brain" partway along the spinal cord somewhat similar to the way a stegosaurus did. The real brain will send a signal to trot, or walk, or gallup, and the secondary structure takes over sequencing of the motor neurons that control the legs. I'm pretty sure that's why it's so incredibly difficult to make a horse go in reverse; it isn't "hard wired".

edit: I just thought of this now. Even weirder is the octopus. It has 9 brains. Each arm has its own, plus one to coordinate them and take care of macroscopic duties such as logic, respiration and vision.