struggle at ccwf.cc.utexas.edu (robotron) writes:
: 1) Since the brain does not have pain sensory neurons, in
: order to feel an ordinary headache (not a stroke), a lot of cerebral
: neurons have to die first, i.e., enough damages must have been done to
: the brain first before you can feel a headache; otherwise, the brain
: can not receive enough inputs to generate a feeling of pain; am I
: right?
:No. While the brain does have "pain sensory neurons" in the sense of
those neurons conveying the information "PAIN!!" when stimulated, brain
tissue does not have sensory pain endings that could react to tissue
damage.
This is an academic view in part, because in the body, "pain" can
result from various chemical substances released from cells, and which
stimulate nerve endings - that send information into the brain - and we feel
pain. Now, if brain damage leads to the release in the brain of various
similar substances, there is cetrainly stimulation of some, and
depression of other neurons, and we feel _something_ - not necessarily
pain, but maybe a pain-like sensation anyway - who can tell?
The accepted view is that nearly all "headache" is not from the brain.
It could be from the scalp (skin outside the skull), from distension of
blood vessels in the scalp, sdistension of blood vessels within the skull
outside the brain, distension of the meninges - but it could also be due
to chemical stimulation of neurons at the surface of or within the brain itself.
: 2) Lipid soluble substances can pass through the blood-brain
: barrier rather easily; thus, if you work in a lab and you can
: periodically smell vapors of substances with low polarity, those
: substances will pass through the blood-brain barrier and will cause
: significant number of neurons to die; as a consequence, you may become
: less intelligent, and you may forget things that you have learned.
: Anyway, how difficult is it for a substance like toluene to kill a
: neuron? and what kind of substance is the most detrimental to the
: neurons?
:Yes. Beware of solvents that are lipid soluble (toluene, styrene,
whatever). In industrial settings (the nylon industry, the paint
industry...) they have destroyed many brains and created near-vegetable
retired ex-workers. The probability of destroying enough brain tissue to
cause any problems is very low in research labs, though, bacause
exposure times are short, concentrations low, and you tend to switch
tasks after a while. "can periodically smell" sounds quite safe to me.
There are substances that are considerably more toxic to the brain
than lipid solvents; however, there is the question of how to get them
into the brain. Those experimenting with drugs are a risk group in this
respect (as shown by for instance the MPTP story).
Dag Stenberg, MD, POhD, Dept.Physiology, Univ.Helsinki, Helsinki,
Finland
