Does CNS in spine have single fiber per inervated muscle?

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Discussion Overview

The discussion centers on the neural pathways involved in muscle innervation, specifically whether a single fiber in the spinal cord connects the brain to an individual muscle, such as those in the toe. Participants explore the complexity of these connections and the potential for multiplexing in the central nervous system (CNS).

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions whether a specific fiber in the spinal cord connects the brain directly to a toe muscle, suggesting that cutting this fiber would stop the muscle's function without other effects.
  • Another participant references a related question from a different forum, expressing frustration over the lack of clarity regarding how the spinal cord manages addressing and routing of signals between muscles and the brain.
  • A different participant asserts that there is not a single neuron from the brain to the toe, but rather a group of connected neurons, noting that muscle innervation typically follows a 1:1 connection pattern, while sensory input may involve more complex "packet addressing" that can lead to errors.
  • One participant introduces the idea that the structure of the spinal cord can vary by species, mentioning horses and octopuses as examples of different neural architectures that affect motor control and coordination.

Areas of Agreement / Disagreement

Participants express differing views on the nature of neural connections between the brain and muscles, with some asserting a more complex network of neurons rather than a single fiber. The discussion remains unresolved regarding the specifics of neural routing and the implications of species differences.

Contextual Notes

Participants note the complexity of sensory input addressing and the potential for errors in this system, as well as species-specific variations in neural structures that may influence motor control.

cave_cat
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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?
 
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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!
 
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.
 
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