how does local compression affect cells?

Question

i've been trying to find that answer in several texts in the net, but i havent found out.
what im talking about goes like this:
when you compress, for example, a nerve or the brain stem, whereas a local tumor or increased intracraneal pressure, there are several reactions (dilated pupils, cardiorrespiratory arrest, etc).
now, what exactly happens? does pressure by itself cause cells damage/lesions? what kind of lesions occur? does compression trigger a response or inhibits neural signals?(like i said, dilated pupils, do they get dilated because the opposite (miosis) signals are inhibited or dilatation is triggered?, the same would go for the rest of symptons and signs associated to local/global pressure.

thanks in advance
rick hunter

Answer 1

It depends how much pressure you're talking about. If it's a great amount all at once (i.e. traumatic), it would probably destroy the cell, and thus act in an inhibitive manner. If it was very gradual, like a tumor, then initially there may be stimulation -- this is seen in tumors adjacent to the spinal cord, in which stimulation of nerves causes pain that may resemble sciatica -- it is called radiculopathy.

However, the tumor (if it keeps growing) will eventually cause intimate impingement on the nerve via compression and produce ischemia (loss of blood supply), damaging the nerve. In your question, it seems like you're referring to Horner syndrome, in which a mass lesion produces compression of the sympathetic nerves in the brainstem and causes the triad of miosis, ptosis, and anhidrosis. In that case, the effects are due to damage of the sympathetic nerves travelling upward from the cervical chain.