Re: [HAPS-L] Cauda Equina

[MITCHELS <MITCHELS@xxxxxxxxxxxxxxxx>]

Title: Re: [HAPS-L] Cauda Equina

I understood that the distinction between PNS and CNS was determined by whether axons were myelinated by Schwann cells or oligos. The beginning of Schwann cell myelination marked the beginning of the PNS. If that is true, then according to earlier posts, the PNS begins at the exit of roots from the ventral horn, and on the sensory side the PNS ends when dorsal roots enter the cord.
Susan

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Susan J. Mitchell, PhD
Professor of Biology
Onondaga Community College
Syracuse, NY 13215
Phone: 315 498-2413
Email: mitchels@xxxxxxxxxxx

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From: "Druzinsky, Robert" <R-DRUZINSKY@xxxxxxxxx>
Reply-To: HAPS-L@xxxxxxxxxxx
Date: Sat, 24 Mar 2007 14:02:37 -0500
To: <HAPS-L@xxxxxxxxxxx>
Subject: RE: [HAPS-L] Cauda Equina

Unfortunately, the distinction between the CNS and the PNS is an anatomical not a physiological distinction.  Alpha motor neurons of spinal nerves have central (CNS) cell bodies and peripheral (PNS) axons.  Sensory neurons of the spinal nerves have peripheral (PNS) cell bodies in dorsal root ganglia and project to the CNS in the dorsal roots to make central connections in the CNS.  By definition the PNS begins at the dorsal (exit) and ventral (exit) zones of the roots.  So, by definition, cell bodies of motor neurons are not centrally located parts of the PNS.  Peripheral nerve damage may cause lower motor neuron signs and symptoms but damage to the cord may cause both lower motor neuron and upper motor neuron signs and symptoms.  
 
Robert Druzinsky, Ph.D.
Associate Professor of Anatomy and Neuroscience
Governors State University
1 University Parkway
University Park, IL 60466 USA
 
Phone:  708-235-2147
Fax:      708-534-1647
Cell:      224-436-0602
 
Email:  r-druzinsky@xxxxxxxxx
 

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From: James S. Miller
Sent: Sat 3/24/2007 10:01 AM
To: HAPS-L@xxxxxxxxxxx
Subject: Re: [HAPS-L] Cauda Equina

That's a very good point.  It certainly makes for clearer understanding if lower motor neurons are all considered part of the PNS.

Jon Jackson wrote:

> Gang: 
>
> With all due respect, I don't think this is a "votable" issue - it's kind of up there with 
>
> You could make the functional distinction as to the rootlets of the cauda equina definitely being in the PNS when one considers damage to this structure. Since the cauda equina consists of dorsal (sensory) and ventral (motor) roots, which get united into spinal (mixed) nerves near the intervertebral foramina from which they exit the vertebral canal, it is easy to imagine a scenario where only the afferent sensory fibers or efferent fibers of these nerves were damaged, say in a penetrating injury.  Such an injury, to a single ventral rootm would result  in lower motor neuron symptoms, i.e. a distributed flaccid paralysis commensurate with the actual number of nerve cells comprising the root; a similarly injured dorsal root would result in a distributed parasthesia, and not upper motor neuron troubles. 
>
> Hence - we're talking PNS here. By physiological definition, not vote. 
>
>
> > I vote cauda equina is PNS. 
> >
> >   

-- 
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James S. Miller, Ph.D.                        Phone: 574-535-7308
Chair & Professor of Biology
Goshen College                                 E-mail: JamesSM@xxxxxxxxxx
Goshen IN 46526-4795 USA                    Web: http://www.goshen.edu
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