Re: Are the dorsal roots parts of the somatic nervous system?

[r norman-4]

On Fri, 17 Jul 2009 20:57:44 -0700 (PDT), GreenXenon
<glucegen1x@...> wrote:

>Hi:
>
>Are the dorsal roots parts of the somatic nervous system?

The distinction between somatic and autonomic is primarily a
functional one.  Do you say that the spinal cord is part of the
somatic nervous system?  Both somatic and autonomic use the spinal
cord and both somatic and autonomic use the dorsal roots.   So the
dorsal roots are sensory, both somatic and autonomic.  However the
sensory side of the autonomic system at the spinal level  is often
ignored in elementary treatments, leaving the impression that the
dorsal roots are  somatic.



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[r norman-4]

On Sat, 18 Jul 2009 08:05:58 -0700 (PDT), GreenXenon
<glucegen1x@...> wrote:

>On Jul 18, 5:13 am, r norman <r_s_nor...@...> wrote:
>
>
>> On Fri, 17 Jul 2009 20:57:44 -0700 (PDT), GreenXenon
>>
>> <glucege...@...> wrote:
>
>
>> >Hi:
>>
>> >Are the dorsal roots parts of the somatic nervous system?
>>
>
>
>> The distinction between somatic and autonomic is primarily a
>> functional one.  Do you say that the spinal cord is part of the
>> somatic nervous system?
>
>
>The spinal cord is part of the central nervous system. The somatic
>nervous system is a division of the peripheral nervous system. So
>*no*, the spinal cord is *not* part of the somatic nervous system.
>However, the dorsal roots are part of the peripheral nervous system,
>so I was wondering if they are also part of the somatic division of
>the peripheral nervous system.
>
>
>> Both somatic and autonomic use the spinal
>> cord and both somatic and autonomic use the dorsal roots.   So the
>> dorsal roots are sensory, both somatic and autonomic.  However the
>> sensory side of the autonomic system at the spinal level  is often
>> ignored in elementary treatments, leaving the impression that the
>> dorsal roots are  somatic.
>
>
>Are there any purely-somatic afferent nerve roots in the human body?

I always found that defining "somatic" to be strictly peripheral a
rather questionable and arbitrary notion.  Does a single sensory
neuron entering the dorsal root suddenly become "non-somatic" the
instant it plunges into the spinal cord?  Does a motor neuron axon
suddenly acquire the "somatic" label only as it enters the ventral
root?   Two microns this way a cell is somatic, two microns the other
way the same cell is not.

However, to answer your question, the facial and trigeminal cranial
nerves are generally considered to be somatic sensory without
autonomic sensory function and the special sensory cranial nerves:
vision, olfaction, audition and balance, taste might be considered
sort of somatic.  Of course these are not spinal roots.

There are sensory cells in the gut which are considered autonomic and
enter the spinal cord through the dorsal roots but I really don't know
exactly how they are distributed across each level of the spinal
column.

It is also difficult to make absolute generalizations about anything
in biology or physiology.  There are lots of very small nerve fibers
all over the place, there are efferent fibers in supposedly purely
sensory nerves and there are reports about dorsal root efferents and
ventral root afferents.



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[r norman-4]

On Sat, 18 Jul 2009 09:52:08 -0700 (PDT), GreenXenon
<glucegen1x@...> wrote:

>On Jul 18, 8:32 am, r norman <r_s_nor...@...> wrote:
>
>> Does a single sensory
>> neuron entering the dorsal root suddenly become "non-somatic" the
>> instant it plunges into the spinal cord?
>
>
>That's another question I find interesting. Sadly, I don't know.
>
>
>> However, to answer your question, the facial and trigeminal cranial
>> nerves are generally considered to be somatic sensory without
>> autonomic sensory function and the special sensory cranial nerves:
>> vision, olfaction, audition and balance, taste might be considered
>> sort of somatic.  Of course these are not spinal roots.
>
>
>Sorry. I forgot to specify my question.
>
>Are there any purely-somatic *tactile* afferent nerve roots in the
>human body?
>
>Tactile = pertaining to sensory phenomenon other than vision, smell,
>hearing, taste, or balance. IOW, 'tactile' pertains to senses of
>touch, tickle, pain, temperature, pressure, itch, movement and pretty
>much any physical sensory entity.
>
>All afferent nerves in the arms, legs, feet, hands, abdomen, chest,
>back and neck are "tactile" nerves. In the head and face are both
>tactile and non-tactile afferent nerves.
>
>Another question is, are there any nerve "roots" outside of the head,
>face, and spine?

The central nervous system consists of the brain and spinal cord so
the only connection to the periphery is through the cranial nerves to
the brain and the dorsal/ventral roots to the spinal cord.

There are more senses than the ones you list.  There are chemical
sensors detecting a variety of things.  There are mechanoreceptors
that don't serve "touch" but are part of the proprioceptive system
monitoring position of the body, force on the tendons, distension of
the gut and other body organs and membranes.  Generally sensors
connected with digestion, defecation, micturation (urination), and the
cardiovascular system are considered autonomic.    As I said, these
autonomic receptors are scattered around the body and I don't know
whether they are restricted to particular spinal roots or are all over
the place.
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