The Neuro Physiology of Stress

ASSOCIATIONS BETWEEN DEPRESSION AND STRESS          
NEJM August 1988

Pain fibers are primary afferent fibers located throughout body, innervate facsia, perimysium and joint capsules., in all tissue except pressue areas eg CNS or intervertabra discs or in cartilage.  Thus ? why not in CNS.

When tissue breaks down in ‘dysfunction’ eg strained muscle or trauma or foreign protein. The archonionic acid comes out membrane and other chemicals eg prostoglandins etc. They attract WBC and cause vasodilate. Eg bradykinines, serotonin, Histimine, prostoglandins, platelet activating factor and Anaphylactoxins.

As vasodilation occurs fluids are excluded and increase pressure occurs. This causes the pain fibres closer to their threshold and primary afferents fire off at a lower rate. Chemicals can also depolirise them, eg, all the chemicals above, so pain can occur as WBC release them and activate Primary fibers. So somatic dysfunction can cause pain.

So we can lower threshold by increase fluid, and the fluid which releases also can fire of the pain fibres. Substance P (polypeptide 10 chain), is released and found in the spinal cord and 80 % of it are produced in the tip of the fibre, as fibre activated the Substance P isd let out in the peripheral. Causes an inflammatory response. So one function of the pain fibres is to create a large pain reponse, by being activated ans vasodilator and bring in more cells. So as you injure something, the response is inflammatory and these fibres propagates itself, the worse it gets the more it drives itself.
So it needs controlling.

Bear in mind the visceral somatic response as the dorsal root ganglion is going to cause release of substance P. Thus somatic dysfunction can be visceral.

Pain fibres go directly into substanan geletinousa. At level of dorsal horn, llarge fibres eg discremating touch go up or down, but the pain small fibres go direct into dorsal horn. So neural code from nerve cell synapse on interneurons go up to brain, but synaspe with with large fibres with touch fibres which stop the fibres. Ie rubbing will reduce pain. In chronic inflamed joint it cuts of the oxegen, which effects the large fibres first as they have higher metabolic rate. Without those fibres it reduces the control mechanism shut of so Pt feels pain with little motion.

At Dorsal horn 3 things can happen, we can get
1.        somatic and visceral reflexes
2.        faciliate a segment
3.        whole body activation.

1.             Autonomic and somatic information overlaps in the dorsal horn. 
Sensory fibers from soma terminate around the autonomics. So somatic dysfunction activates autonomic tone in viscera. Sato in Japan, placed canula pressure sensor in rat, and took tissue forceps and pinched rats skin. As he pinched in abdomen it reduced pressure in the stomach. The sympathics are inhibitory so they shut stomach area. Over the cranial and sacral regions of the rat it increased pressure in the stomach. So he could drive stomach muscles from the peripheral. Cutoneal urinary and cutanoa cardiac and cutaneal gastrointestinal.
2.                    Fascialtated segment. Sensory information activates interneurons in dorsal horn. They go to ventral horn. Eg big alpha neuron’s innervate extrafusal muscle in soma. Or small gamma fibres eg. intrafusal muscle eg. spindles. You can inject a joint with irritant, and can record from dorsal and ventral horn cells with elecrodes. The fibres were fired from ventral and dorsal cells which lowered the primary fibres and thus increase tension and tone around the joint and the joint is held out of position by lowered threshold. The small gamma fibres were also effected some increased their threshold and some decreased. Eg Flexors increased and extensors decreased.  Even when the small pain cells were removed the big neurones still fired ie they were fixed. The interneorns were help by interneurons. Somatic movement might unfix this pattern.
3.                    By restricting the motion of the joint we effect the body. Information goes from spinal cord upwards. ‘Suprasegmental activation’. From dorsal horn cross over and go up. Spinalthalemic fibres. Eventually get to thalmus. First instant feeling of pain is tearing pain and localising pain to pariental lobe, second pain is slower and nausea pain and that is slow pain into frontal area unspecific and whole arm or body hurts makes you concrened about pain. Thalamic pain can occur if elimate fibres to patienatal localising lobe eg from a tumour. Treatment would be surgical to remove thalmus areas.  Large fibres can give discremative touch and small fibres also go to ventral posterior fibres. Activate various areas, can go to hypothalmus which should warn and learn it.
The body needs to control the inflammation. So we bring in the endocrine system.